High Voltage Forum

General electronics => Electronic circuits => Topic started by: petespaco on December 23, 2018, 05:49:46 AM

Title: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on December 23, 2018, 05:49:46 AM
I have been experimenting the the popular "12-48 Volt 1000 Watt ZVS Induction heaters" for a year or two and have many videos and web pages describing that work, as many of you may know.
   More recently, an improved version has become available and is being sold by well over a dozen vendors.  Instead of one pair of IRFP260N's driving the coil, they doubled up on them and added 2 fans on top.  The also added 50% more capacitance to the  tank circuit and increased the number of turns of the output coil from 7 to 10.  These tank changes should lower the oscillation frequency which is good for many things that people would want to heat.

  Just recently, I ordered one of them, a complete kit, called "Combo 2" by seller Aliexpress.
I had to wait quite a while for an analog ammeter and it’s here now.  I still haven’t connected it all up yet, but I have spent a lot of time unraveling the various  descriptions and pseudo instructions that I see on the vendor offerings.  These units are seldom soldi n as complete a kit form as the one the I got from Aliexpress.
Some vendors call them 1800 watt, some even call them 2500 watt, but I’m pretty sure they are all the same.
  Yesterday I put up a new web page to help new buyers understand what they just bought and how to set it up with a minimum of disappointment.
I tell you all this, because I’d like to get this link to others, since I am already getting inquiries anyway.
There are two web pages referenced here on this cover page:
 https://spaco.org/Blacksmithing/ZVSInductionHeater/ZVS1800Watt/1800-2500WattZVSInductionHeaterNotes.htm

Both pages are pretty messy, but, due to the apparent popularity of these devices, I wanted to get something out there.
Time will tell.

I will add to that page and to my youtube channel once I get my system up and running.

Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on December 23, 2018, 05:35:44 PM
You got my attention with this, there has for a long while been small ZVS drivers available, but these "high" power seems more interesting as the price-tag is getting closer to what you could build a similar unit for yourself.

I looked at "1800W 40A ZVS Induction Heating Board" on ebay and it seems to be the exact same unit as your 1800W model, on some pictures for the 2500W model it looked like it was 120mm fans on top and it had a 3rd heat sink in the middle, so just from the pictures it must been built bigger for then higher power rating.

I placed a best offer on one of them and will see how cheap I can get one from China, as I got a few different "cheap" power supplies that I wanted to test on a ZVS induction heater before telling the world about it is a possibility :)
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on December 25, 2018, 09:17:31 PM
Good eye, Mads.
   Yes, I now see the extra heat sinks and additional pair of gate resistors.  So now it looks like 3 Mosfets in parallel on each side.
And I also now see that the 1800 watt model  has 90mm fans, versus the 120mm fans for the 2500 watt model..
I can only say that I did some  sloppy investigation!
I'll already updated  my pages to reflect this difference.

I will look forward to your comments when you get your board.
By the way, we have all heard the warnings about NOT connecting these zvs heaters directly to a switched mode power supply and then plugging the power supply in.  They say that the slow start characteristics of the SMPS cause it to start slowly and cause the mosfets to lock up.
And I am sure that is generally true.  But the server power supply that I got with my Aliexpress heater (Emerson 48-2900U Switched mode Power Supply)
doesn't even turn on until about 7 seconds after power us applied.  I will probably set my system up to power the supply first anyway, just to be safe.

(a bit red-faced),
Pete Stanaitis
   
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on January 02, 2019, 01:54:03 AM
Hello, Mads.
I hope I am not getting ahead of myself here, but I see a new issue with both the 1800 watt and the 2500 watt versions of these ZVS heaters.
  It has to do with the little buck converter that runs the fans, and in the case of the one the I bought, the pump.
Here's what I have to say:
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Important note if you intend to run your heater on 48 Volts:
You can NOT use the little power supply (buck converter) for the fans! You will have to provide a separate 12 volt supply at a couple of amps.
That is because the maximum rating of the regulator chip on the buck converter board is 40 volts. Don't ask me why they did that, but, hidden in the Chinglish, is a warning that operation at voltages higher than 36 will "burn" the fans and/or pump.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
I'm getting closer to powering the thing up.  I checked the no load current draw of the pump and its only about 300ma, but I will need to connect it to the actual system and fill it with water to see how much current it will draw,  Then, same for the fans.  Then find or make a simple power supply for them.

Have you noticed this situation, and what is your feeling about using that buck converter?

Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on January 03, 2019, 12:09:11 PM
Thats a pretty important detail you discovered there, thank you for sharing.

I am still waiting for my mine to arrive, hopefully I wont get hit by the Chinese new year in February as ebay has it stated as shipped off on 25th December 2018. But still it says Estimated delivery: Tue, 08 Jan - Tue, 19 Feb
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: flyrod on January 05, 2019, 03:46:29 PM
What is the chip on the DC-DC converter?  I'm guessing it's a LM2596.  It could be a high voltage version of the same thing: LM2596HV which would take 60v or so.  Does it look like this:?

(https://i.ebayimg.com/images/g/V2oAAOSwKb1bPyOK/s-l1600.jpg)

From here:

https://www.ebay.com/itm/123560506283

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on January 05, 2019, 05:27:23 PM
Thanks for your question, flyrod.
  Yes, the chip IS the "LM2596HVS" version.
That makes the Chinglish warning about not using the converter when the input is over 36 volts even more confusing..
When I looked up the datasheet a couple of days ago, i googled "LM2596" and got this:
http://www.ti.com/lit/ds/symlink/lm2596.pdf
I didn't look beyond the first few pages when I found the max input voltage to be 45.
I even found another datasheet when it was spec'd at 40:
https://www.onsemi.com/pub/Collateral/LM2596-D.PDF

It didn't occur to me that to investigate the "HV".  Sorry, I hope I didn't cause too much confusion.  I guess I was biased by the warning that I mentioned earlier.
http://hmsemi.com/downfile/LM2596HV.PDF

  By the way, my buck converter doesn't have the pot.  There's a fixed resistor in its place.

I did fire the system up yesterday and it worked, BUT the idle current (current flow with nothing in the work coil) is at 26 amps.  I think it should only be about 6 amps.  It IS oscillating. When I put a graphite crucible into the work coil the current does increase to 40 amps.  Frequency is about 77Khz, by the way.
I have attempted to contact the vendor through aliexpress.  We will see how that goes.

For that initial test, I did add a radiator and  unplugged the buck converter and powered  the fans and pump from a separate supply, just in case.

Sorry for jumping to conclusions,
Pete Stanaitis
---------------

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: flyrod on January 06, 2019, 12:34:15 AM
Can you tell what the gate drive is on your new board?  Is it the same pull-up resistors as on the little boards?

How are you measuring 26A?  Could you be using a different shunt that needs calibration maybe?  If 26A is accurate, that's a lot of power going somewhere.  Does anything besides the work coil heat up quickly?  For example if one of the caps is defective, 1000w should pop it in short order and make the problem clear.  A shorted turn in the work coil could also explain it.

Good luck in your experiments.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on January 06, 2019, 07:11:25 PM
i just checked the current by adding a direct reading ammeter in series with the shunt meter.  The readings are the same, within a couple of amps, since the scale on the new meter is fairly coarse.
  Haven't yet dismantled the board to look at circuitry, or to scope the gates.  The way this thing is made, you can't see inside much because the 4 heat sinks cover the sides and the fans cover the top.  when I do dismantle it, I probably should bring out a couple of test points.
I was hoping that I wouldn't have to dig into the thing at all.
No feedback from the Chinese vendor yet.  Is it Chinese new year right now?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on January 07, 2019, 08:17:44 PM
Today I examined the heater by eye and with an ohmmeter.  Can't yet see any reason why the idle current should be so high.
   Circuit components are identical to the 1000 watt board, Just twice as many.  Except that there are 9 of the 0.33 ufd capacitors and a 10 turn 60+ mm ID work coil.
Stumped.
   I did see one video where the guy was testing an 1800 watt board with an ammeter in the ckt.  That's where I got MY "expected" 6 amps idle current from.  That and the fact that my 1000 watt heaters do about the same.
  I may try a smaller diameter work coil just to see what happens.
But I am still hoping for some sort of feedback from the vendor.  Chinese new year for 2019 (year of the pig) apparently does not start for a few weeks yet:
Jan 28 to Feb 19.
  I now see that I can get the gate signals from the bottom of the board, so I can look at them once I get my courage up.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on January 10, 2019, 05:33:48 PM
Yesterday I added a short lead to each gate of the Mosfets so I could scope them.  I didn't change anything else, but when I fired it up, the idle current is only  about 14 amps instead of the 26 amps that I had previously!  Then, when inserting the crucible, the current went up to  36 amps instead of the previous 40 amps.
 The gate signals are all pretty good looking square waves and they are all the same.
Why the change???---  I don't know, but all I did was to solder those gate leads in place.  Bad joints???

The aliexpress vendor didn't seem to pay any attention to my problem description.  They emailed me back to say:
"friend , can you tell us in aliexpress message ?"
Aliexpress customer service, by the way, seemed very concerned when I chatted with them about the issue earlier.  But all they did was to pass my concerns on to the vendor.

I did make a short video of the the above and may put it up on youtube as a troubleshooting aid.
If anybody who is viewing this message has one of these 1800 watt or 2500 watt ZVS heaters running, please tell me what YOUR idle current is.

Thank you,
Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on January 11, 2019, 05:10:39 AM
Well, it is finally up and running properly.
 Drawing about 4 amps idle current (still using 48 volt power supply), then goes to about 35 amps with crucible fully inserted.  Now need to mount a fan on the radiator and do a few other things.  Hate to say it, but I am not certain what caused the difficulties.  Later in my troubleshooting, I discovered that two adjacent turns of the work coil were touching, but separating them didn't help.  I took the fans off to get at the coil so I could insulate it with high temperature fiberglass sleeving.  When I put it back together, it works fine.
Maybe a cracked foil on the board?  Don't know for sure.

Next steps if it continues to work properly:
  Shoot for max current of about 40 to 45 amps.
Place fire brick below coil
  Try some steel  (to max out current) and to see how quickly it heats things to 1200° C.
1" Sq.
3/4" pipe  (pipe heats real fast since its a one turn "coil"
Melt some copper.
   Make a crucible cover. 
   Find/make tongs for pouring.
   Make a simple open face mold?

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on January 14, 2019, 12:22:07 PM
My first impression of the 1800 Watt IH is not great.

- The whole PCB is bent in a curve due to the fans+mount is bigger than the holes for it on the board.
- One of the input inductors had broken off the PCB from rough shipping.
- Connector to the fan controller was destroyed and broken off the board.

Returning the product is more expensive for me than its worth, so I filed for a refund and seller only gave me a laughable 5$ refund out of 50$. For that he will earn a negative review. For others warning, I bought from "Gowin Electronic" ( http://www.ebay.co.uk/usr/gowin_electronic?_trksid=p2057872.m2749.l2754 ): https://www.ebay.co.uk/itm/1800W-40A-ZVS-Induction-Heating-Board-Module-Driver-Heater-With-Heat-Sink-Kit/312211105813?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Shipping was fast, seller communicates fast aswell, but they are not giving up any money without a fight.


I will repair and test it later.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: the_anomaly on January 14, 2019, 01:15:53 PM
I have also just purchased one, Yosoo 1000W by huhushop on Amazon.  Bought it Sunday morning, got it delivered Sunday evening.. man I love Amazon haha.

Looks ok except one of the FETs is not fully secured to its heatsink; the screw is only part way threaded in.  Also no thermal compound, Mads does your unit have thermal compound on the FETs?

As long as I can use it to heat stuck bolts on this outboard engine I am repairing I will be happy.  I've been tempted to build Uzzors PLL induction heater http://uzzors2k.4hv.org/index.php?page=pllinductionheater1 (http://uzzors2k.4hv.org/index.php?page=pllinductionheater1) but I took this gamble to hopefully save time and money. 

One thing I've been warned about using ZVS induction heaters is you need a power supply with a fast turn on transient otherwise oscillation may fail to start and resulting in both FETs turning on at the same time.  Probably best to connect the power supply to the induction heater through a relay so you can turn on the power supply, let it fill its output filter caps and then activate the relay.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on January 14, 2019, 05:08:38 PM
Mads-  Sorry to hear about your shipping issues.  I did get one or two of the 1000 watt units where one lead of  the 470 5 watt resistor had broken off the board.   The buck converter terminal on your board is different from any I have seen.  That makes me wonder how many actual manufacturers are in this game, and how much actual thought goes into each one's design variations.

the_anomaly-  I assume you will need to have some flexible way to get power and water cooling to your work coil if you plan to heat stuck bolts.  Please keep us/me informed on how you do that. 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on January 16, 2019, 04:26:38 AM
It's working fine now:
/>
Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: the_anomaly on January 17, 2019, 02:01:36 AM
Nice video Pete!  I am actually not planning to use water cooling, probably 12-14ga solid copper wire.  I am hoping that using it only for a minute at a time will be sufficient to get a 7/16" bolt red.  Hopefully this will be a short enough duty cycle to keep the coil from melting.  If I do need water cooling I was planning to go to the auto store; they usually stock 1/8" copper tube for oil pressure gauges.  Since space is tight for my application, I need to use a smaller coil.

Is that a South Bend lathe in the background?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on February 18, 2019, 12:13:02 AM
Thanks for the kind words.
  I should have gotten back to you sooner.
I don't think the coil will melt in 30 seconds or so, but it will transfer a lot of heat back to the standoffs that it is connected to.
When you say "get a 7/16 inch bolt red", do you meant just the head or a whole bolt?  And, how hot is "red"?   If it just needs to glow a low to medium read color to the naked eye, you should be okay,  But if you need it to be bright red or orange. it can take quite a while, once the bolt's temperature passes the "curie point", becoming nonmagnetic.  That's because the heating rate will slow considerably.
  if you plan to use a work coil of less than 7 or 8 turns, please let me know how it works out. 

That's an Atlas 10F lathe in the background.  Wish it was a South Bend, but it works for me.

Pete Stanaitis
---------------   
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on March 07, 2019, 01:26:47 PM
I finally got around to get the IH out of the box and repair it, here is part 1 of a series of videos on this IH.

The future parts will be power supply building and testing.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on March 07, 2019, 03:51:16 PM
Hello Mads.
  Putting the standoffs on the bottom is a good Idea.  I wish I'd have thought of that.

It is interesting to see how many slightly different implementations of these devices exist.  Your device is the first one I've seen where the work coil is oriented horizontally.
On my 1800 watt unit, there was no heat sink compound, but they did have piece of thin, white material sandwiched between the Mosfets and the heat sink.  I thought about replacing that material with heat sink compound, but so far it hasn't been a problem.  I did blow up one Mosfet, but that was my own fault for paralleling one gate with too low of a resistance.  I knew better, but did it anyway.  Such is the life of a novice!

By the way, I just powered  up my 2500 Watt ZVS induction unit and did a youtube video of it yesterday.
It is here:
/>You will see my messy method of getting the water away from the board.

Pete Stanaitis
---------------

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on March 09, 2019, 08:28:48 AM
I built my first experimental cheap power supply and it was a great success!

12 laptop chargers put together for 40V 51A.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: flyrod on March 10, 2019, 04:09:25 PM
I did blow up one Mosfet, but that was my own fault for paralleling one gate with too low of a resistance. 

So do these boards use the same pull up resisters for gate drive?
 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on March 11, 2019, 08:22:21 AM
5 minute stress test at full power. 1800 Watt peak input power.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on March 11, 2019, 03:17:35 PM
Flyrod: "So do these boards use the same pull up resisters for gate drive?"
If you mean "do they use the same gate drive circuit as does the 1000 watt unit?"
Yes, for the 1800 watt unit that I have, at least.
The same 470 ohm 5 w wirewound resistor, 10K resistor, 12 volt zener  and FR307.

If you mean: "do all 4 gate drivers use the same pull up resistors for gate drive?"
The answer is still "yes".

Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on March 15, 2019, 08:49:01 AM
A new 2200 Watt power supply made from server power supplies, and with steady cameras :)

Test of it in a long induction heater run is being edited and will come online in a few days

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on March 18, 2019, 10:35:04 AM
/>
This test is being run at 36VDC and everything stays cool over a course of 10 minutes, I would say it can run stable at this power input. The 5 minute test at 40VDC showed resonant capacitors heating up.

Test is powered by the "2200 Watt server power supply for induction heating"
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on March 18, 2019, 06:11:07 PM
That sure was a successful test.
    Is the "glowing" color that we see on the video that same as what you see in person?  Do you do anything special with the white balance of your video camera?

I am starting to work on establishing operational upper frequency limits on these devices.  I wonder how high they can go and still work okay.  Today, I certainly exceeded that number, so now I will have to "back up" to see where the real tripping point is.
So far, I hypothesize  that the data I gather from the 1000 watt unit will transfer directly to the 1800 and 2500 watt devices, since their gate circuits appear to be identical.  (Having said that, and seeing that two of three gate circuits are in parallel, I WILL have to verify that some day.)
By the way, I am using a cheap inductance meter for these measurements.  I think it is this one:
https://www.ebay.com/itm/LC100-A-High-Precision-Digital-Inductance-Capacitance-L-C-Meter-Tester-SMT-Clip/253959986062?hash=item3b2131db8e:m:mOpTSkV_q1oIM9pHKxVlPfw

Here's the record of this morning's test:
Objective:
  Determine the lower work coil inductance range for safe, useful operation of the popular 1000 Watt to 2500 Watt ZVS induction heaters.

Date: march 18, 2019

Subject for testing, March 18, 2019:
Testing a 10" U shaped work coil on the 1000 watt unit.

Method:
Make up a "one turn" coil to use as a worst case situation.  This coil is simply 25" of 1/4" OD copper tubing that is bent into a "U" shape, with about 3/4" between the arms.

Summary:
My initial conclusion is that the oscillation frequency observed during this test is somewhat beyond the safe or useful upper limit for this design.
  I hypothesize that the lower limit for work coil inductance is about 1.0 microhenry.
-----------------------------
Notes:

First I checked out the system using a "stock" 2" ID 6 Turn coil.  It ran, as it normally does,  at  about 6 amps of idle current.

Then I removed the 6 turn coil and replaced it with this "U" coil:
The measured inductance of this "U" coil is about 0.240 micro henry.
At present, the coil is actually several inches longer than 10.  I call it a "10 inch coil" because, once fully shaped, it would have a work area about 10 inches long for heat treating knife blades.
It has a spacing between the tubes of about 3/4".

For reference, these 1000 watt ZVS heaters come with coils that produce resonant frequencies between about 103 kHz and about 83 kHz.  These coils have measured inductances of about 1.05 to 1.38 micro henry.

Results:
The system  DID oscillate, but at about 154 kHz. 
And the gate waveform degraded significantly from the almost square shape it has with the "stock"  6 turn X 1 1/2" to 2" ID coils.  The signal almost looked like a sine wave with a slightly flattened top, both the leading AND the trailing edges.

  The idle current went to 16 amps.  I think this extra 10 amps is caused by the degraded gate signals causing the Mosfets to be running in linear mode for a good share of the time.  Also, the capacitors heated rapidly within a minute or so of "power on".


Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on March 20, 2019, 12:41:22 PM
That sure was a successful test.
    Is the "glowing" color that we see on the video that same as what you see in person?  Do you do anything special with the white balance of your video camera?

It seems I have rather good UV filters on my phone and DSLR, as you actually see a red glowing work piece in the video and not a purple glow. It does however not filter it all, it does glow more bright on the video than in reality and I guess you have the same experience.

I am starting to work on establishing operational upper frequency limits on these devices.  I wonder how high they can go and still work okay.  Today, I certainly exceeded that number, so now I will have to "back up" to see where the real tripping point is.
So far, I hypothesize  that the data I gather from the 1000 watt unit will transfer directly to the 1800 and 2500 watt devices, since their gate circuits appear to be identical.  (Having said that, and seeing that two of three gate circuits are in parallel, I WILL have to verify that some day.)
By the way, I am using a cheap inductance meter for these measurements.  I think it is this one:
https://www.ebay.com/itm/LC100-A-High-Precision-Digital-Inductance-Capacitance-L-C-Meter-Tester-SMT-Clip/253959986062?hash=item3b2131db8e:m:mOpTSkV_q1oIM9pHKxVlPfw

Here's the record of this morning's test:
Objective:
  Determine the lower work coil inductance range for safe, useful operation of the popular 1000 Watt to 2500 Watt ZVS induction heaters.

Date: march 18, 2019

Subject for testing, March 18, 2019:
Testing a 10" U shaped work coil on the 1000 watt unit.

Method:
Make up a "one turn" coil to use as a worst case situation.  This coil is simply 25" of 1/4" OD copper tubing that is bent into a "U" shape, with about 3/4" between the arms.

Summary:
My initial conclusion is that the oscillation frequency observed during this test is somewhat beyond the safe or useful upper limit for this design.
  I hypothesize that the lower limit for work coil inductance is about 1.0 microhenry.
-----------------------------
Notes:

First I checked out the system using a "stock" 2" ID 6 Turn coil.  It ran, as it normally does,  at  about 6 amps of idle current.

Then I removed the 6 turn coil and replaced it with this "U" coil:
The measured inductance of this "U" coil is about 0.240 micro henry.
At present, the coil is actually several inches longer than 10.  I call it a "10 inch coil" because, once fully shaped, it would have a work area about 10 inches long for heat treating knife blades.
It has a spacing between the tubes of about 3/4".

For reference, these 1000 watt ZVS heaters come with coils that produce resonant frequencies between about 103 kHz and about 83 kHz.  These coils have measured inductances of about 1.05 to 1.38 micro henry.

Results:
The system  DID oscillate, but at about 154 kHz. 
And the gate waveform degraded significantly from the almost square shape it has with the "stock"  6 turn X 1 1/2" to 2" ID coils.  The signal almost looked like a sine wave with a slightly flattened top, both the leading AND the trailing edges.

  The idle current went to 16 amps.  I think this extra 10 amps is caused by the degraded gate signals causing the Mosfets to be running in linear mode for a good share of the time.  Also, the capacitors heated rapidly within a minute or so of "power on".

Thanks for doing these experiments with lower inductance work coils and the resulting frequencies and currents. As expected it heats up a lot from increased switching losses due to more time in the linear region, but also it did not explode! I had expected it to burn to ground from your U turn coil :)
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on March 21, 2019, 07:09:05 PM
Hello everyone!
Another induction heater enthusiast here... I recently purchased the 1800 w unit and was going through all the info everywhere (that spaco.org website was of enormous help, many thanks!)
But anyways... there are several things that I am not so certain about.
First of all, seems like everyone is using switching power supplies (servers or that crazy combo of a dozen laptop power bars=) ... I looked up the price + shipping for the server supply and shipping costs are more than the unit. I started to think, what can I power this with, all the high current supplies are quite expensive.
I got an idea to use one of those "voltage converter" units (europe/us) which is essentially a 1:2 transformer depending which side you connect to. So it should half our 110V into like 55V which is close enough. I am thinking of connecting a diode brigde/cap to that to make it a nice ripply DC and then use a zener to regulate final output to no more than 48 V. Does that sound sensible? As I understand, the ZVS unit will only draw as much as it needs, depending on what is going on the the work coil.
The other thing is, my fans are connected to the board, there s no controllers or anything in the vicinity of the connection - . Debating whether to use a separate supply with them or not if I go for 48 V. They even ziptied the wires to the posts.
When I get all the parts, I will make a youtube video using all this=).
 



 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Hydron on March 21, 2019, 07:51:23 PM
Unfortunately that's not really a viable way to build such a supply. Firstly those voltage converter units are normally autotransformers, with no isolation from mains input - you have to treat it just like you would mains (regardless of voltage) so very unsafe for a job like this. Secondly any linear regulator on the output would have to be very large to deal with the current.

As for the availability of server power supplies, they do sometimes come up cheaply when an older server is scrapped and sold off in bits. As you said though, shipping can hurt. If you can't find something else suitable then a few large lead acid batteries in series could be a candidate at least for use in testing.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on March 21, 2019, 11:04:48 PM
Sadly, I already purchased the unit=( and only then came accross this forum. Oh well, I can return it or...
I could'nt find any pictures of the insides, but a closer look at the ebay posting - it looks like it's a torus inside. Hard to tell from the picture. Maybe there is an option to modify it into a proper transformer with prim and sec windings.
Regarding zeners, I am thinking to wire about a dozen of them in series which should crank up the tolerable wattage to about 14W. Also possibly immerse them in something cold if needed.

Well , I understand it all sounds like not a great idea, but since the unit is being shipped I can at least peak inside and maybe ship it back, and stick to SLAs or something.

I knew this is going to be an adventure...
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on March 22, 2019, 10:56:16 AM
Hi Peter and welcome to HVF

I got a good collection of server power supplies and have more than I need. I can ship 2kg for 15 Euro, it might take 2 packages to ship 3 of them, but send me a PM with your offer for 3 power supplies that would give you 36V at 60A, you could also tinker with them to adjust them up to about 40V in total.

But generally you are not going to get good results with a Royer IH when using a weak power supply, this oscillator will eat all the power it can get and will just pull down the voltage of the power supply if its too weak, which can lead to failure if the voltage drops under 10VDC due to linear switching/uncertain gate state.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: kamelryttarn on March 22, 2019, 11:25:19 AM
Hello everyone!
Another induction heater enthusiast here... I recently purchased the 1800 w unit and was going through all the info everywhere (that spaco.org website was of enormous help, many thanks!)
But anyways... there are several things that I am not so certain about.
First of all, seems like everyone is using switching power supplies (servers or that crazy combo of a dozen laptop power bars=) ... I looked up the price + shipping for the server supply and shipping costs are more than the unit. I started to think, what can I power this with, all the high current supplies are quite expensive.

You could also do like I did and just take an old welder. Voltage and current ratings are often close to what these inductions heaters use.

https://highvoltageforum.net/index.php?topic=32.0 (https://highvoltageforum.net/index.php?topic=32.0)
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on March 22, 2019, 03:46:16 PM
You might also try rewinding some 1000 watt Microwave Oven Transformers  (MOT).  You could rectify their output.  I don't know how ripple free the power to these induction heaters needs to be, so I don't know how much capacitance it would take to smooth it.  But, if you did use lead acid batteries, they  would be a good ripple reducer, I'd think.    Then your "MOTs"  would simply be acting as a battery charger.
   I would suggest simply going the MOT route with a lot of capacitance  (just under the amount that would trip the mains breaker on power up), but, if you have to buy them, you might as well simply buy the server power supply anyway.
  Depends on how much tinkering you want to do.
  I tried to find the unit that you (badpeter) ordered on Ebay.  I think I found it, since it was the only one I saw that had the fan wires zip tied to a post.  I didn't see any place on the back side of the board where   the buck converter parts might be located.  But it could be hiding in there someplace, I suppose.
  Was it this one?:
https://www.ebay.com/itm/1800W-ZVS-Induction-Heating-Board-Module-Flyback-Driver-Heater-Tesla-Coil-Fan-US/123420945506?epid=2291469563&hash=item1cbc762c62:g:D2UAAOSwFnxbwEuo
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on March 22, 2019, 08:19:21 PM
Microwave is an option that was considered, if I find one laying around, definitely ripping out the transformer. Not too certain how much work i'd need to do winding the thing to the proper voltage though. I got lots of caps, so can add quite a bit of capacitance. And yes, that looks like the unit I got, except it was a different seller. Board is covered with finish so no way to trace anything. And strange words on the back "Is strictly prohibited". I guess we'll never know what is...=)

Re server power supplies, I am potentially interested. Will send ya a message!

By the way that voltage converter unit that is still in shipping is rated for 3 kw, so it should supply enough power even for a bigger unit. Here i am limited by my 40 amp breakers in the apartment. Will have to connect it to the outlet on the stove, if i decide to use it at all.
I will test everything and run a dummy load trying to get 40 amps at correct voltage, to see that it is capable of producing that.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on March 23, 2019, 01:50:47 AM
MOT:  There are plenty of youtube videos out there abut rewinding MOT's.  Good that you have lots of capacitors.

Work safe and "keep one hand in your pocket" when working with high voltages.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on March 25, 2019, 03:45:43 AM
I received my "donut" and I think I will keep it for now! (picture).
It is a center tapped auto transformer, nice thick wire. Halves the voltage as expected. I  DC-fied the output via a bridge and recorded the following:
no load=57v,
49.1V at 5.2A  (258 va)
41.4V at 11.4A (465 va)
this is far from the advertised 3000VA, but i think V*I can still get a bit better with higher current, towards the middle of the range. I cannot however measure higher currents at the moment to confirm that.

What i can do is unwind some of the wire to make it exactly 48 volts instead of 55. But seeing how I kind of get 48 v at 4 amps anyways, do I even need to do that? maybe a bit of overvolt is alright.   

Once i get the proper high current diode bridge from china, I think can fire up the induction board!
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on March 28, 2019, 04:27:17 AM
Even if you get 12 or 15 amps at about 40 volts, you have to subtract about 6 amps for idle current , leaving only 6 to 9 amps to do heating of the work.  That isn't very much.  That's only about 240 to about 360 watts.  Something doesn't sound right .
  I would also be concerned about using an autotransformer without an isolation transformer in between.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Hydron on March 28, 2019, 09:34:40 AM
Running direct from mains is extremely unsafe for something like an induction heater where you may contact the work coil by mistake.

There have been plenty of other suggestions that are much safer, go for one of those!
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: kamelryttarn on March 28, 2019, 11:00:02 AM
Even if you get 12 or 15 amps at about 40 volts, you have to subtract about 6 amps for idle current , leaving only 6 to 9 amps to do heating of the work.  That isn't very much.  That's only about 240 to about 360 watts.  Something doesn't sound right .
  I would also be concerned about using an autotransformer without an isolation transformer in between.

Is the efficiency and idle current constant? Ie, if you have 6A idle current, is the "wasted" energy constant even when you insert a work piece or is it possible that the efficiency actually increases when there is something in the coil to transfer energy into?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on March 28, 2019, 01:29:52 PM
Quote
Is the efficiency and idle current constant? Ie, if you have 6A idle current, is the "wasted" energy constant even when you insert a work piece or is it possible that the efficiency actually increases when there is something in the coil to transfer energy into?

No, I don't think the "wasted" energy is constant.    What I do know is that, when you place a work piece into the work coil, the components on the board get hotter, so there's actually MORE "wasted" energy at that point.  And, I don't account for it very well.
  You ask a good question.
  I don't know how I would measure  "EFFICIENCY increases".
At least with these ZVS heaters, there's a lot going on when you insert something into the work coil.  With the current draw from the power supply increasing and the frequency changing, a little or a lot, depending on the material that the work is made of.  Then there's the heat extracted from the components on the board by the fans, and, of course, the heat radiated by the work itself, some of which goes to the work coil cooling system and some into the air.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: DICKEYBIRD on March 30, 2019, 01:42:45 PM
'Morning all & Happy Saturday!  Newbie here. :)

Today I'm working on a PS for my recently purchased 1800W unit.  After seeing Mads videos, I obtained some HP DPS-750RB PS's and am performing the isolation mods as I type this.  I understand everything except for what to do with the ground pigtail that was captured under the of longer of the board mount screws.  Should it be clipped off & discarded or reinstalled under the nylon insulator?

I noticed on another forum that it's recommended to leave one of the series connected PS's un-modded (not isolated) but Mads modifies all 3 in his video.  It looks like either way will work but is one preferred over the other?

(Edited to add another query)
All the mosfet mount screws were completely loose (.5mm gap between it and heatsink!)  Is the white "paint" on the face of the mosfet enough of a heatsink compound or should I add some?

...and thanks for what you guys do here!  I have nothing to offer electronically but I am a hobby machinist & and lifetime tinkerer. :)
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on March 30, 2019, 06:04:30 PM
I would not add any more heatsink compound.  Although most heatsink compounds are non conductive, make sure that none of it can touch the Mosfet leads, just in case.   If I understand the heatsink compound  "science" correctly, its only task is to fill in any tiny gaps between the device and the heatsink, to promote maximum heat transfer.
  Certainly do snug up the screws.
By the way,  I use a pair of "Snap-on 105 Ignition pliers"  to loosen and tighten the Mosfet mounting screws, since they are so hard to get at in the 1800 watt and 2500 watt ZVS units.

Capacitor safe working temperature-  I found this:
"The normal working range for most capacitors is -30°C to +125°C with nominal voltage ratings given for a Working Temperature of no more than +70°C especially for the plastic capacitor types."
  Even 70°C  (158°F)is well over the temperature where you can hold your hand on the part.
It would be good if some of you can read the temperature of the capacitors during extended runs to see how hot they actually get, and to see if the temperatures stabilize during a run.
In my case,  The capacitor temps do seem to stabilize close to acceptable values:
 [ Invalid Attachment ]
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on March 31, 2019, 09:46:10 PM
'Morning all & Happy Saturday!  Newbie here. :)

Today I'm working on a PS for my recently purchased 1800W unit.  After seeing Mads videos, I obtained some HP DPS-750RB PS's and am performing the isolation mods as I type this.  I understand everything except for what to do with the ground pigtail that was captured under the of longer of the board mount screws.  Should it be clipped off & discarded or reinstalled under the nylon insulator?

I noticed on another forum that it's recommended to leave one of the series connected PS's un-modded (not isolated) but Mads modifies all 3 in his video.  It looks like either way will work but is one preferred over the other?

(Edited to add another query)
All the mosfet mount screws were completely loose (.5mm gap between it and heatsink!)  Is the white "paint" on the face of the mosfet enough of a heatsink compound or should I add some?

...and thanks for what you guys do here!  I have nothing to offer electronically but I am a hobby machinist & and lifetime tinkerer. :)

I just left the little wire hanging out in the air, not connected, so I might aswell just have cut it off, they seems to work just fine without it.

You are right that one power supply can be left un-modded, the one that sits in the negative end of the chain, I am however not sure if that would put a limit on how many you can put in series, but I would personally not try for higher than 60 VDC with 5 in series. Solely based on assumptions about creeping distances on the PCB being relatively low for a 12V product.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Hydron on March 31, 2019, 10:23:26 PM
I'd personally ground (by not modifying) the supply in the middle of the chain - that way each end is only half the voltage with respect to earth. This would not work if you had to put a non-differential scope probe on the IH though.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: DICKEYBIRD on March 31, 2019, 11:51:05 PM
Thanks fellows for the learned advice!  I'll clip those wires since it will be less likely for my Klutzy self to short out something important.  I think I will leave 1 of the 3 PS's un-modded...that fits my laziness perfectly; only one more to go!

The project is coming along pretty well. I was able to remove the original MOSFET screws & replace them with M3 SHSC's so that they could be torqued with a cut-down allen wrench without de-soldering any parts for access.  The screws on the DC terminals were replaced with SHSC's as well so they could be tightened properly.

I "dumpster-dived" a dead automotive battery charger at my day job recently.  After stripping out the old dead Chinese electronic parts, I am now installing some (hopefully not-so-dead) new Chinese parts.  I procured a small, cheap auto heater core and am installing it behind the louvered side panel on the charger case with a couple 12V PC fans for cooling, a small 12V pump & a 1 gallon can of distilled water.  I should have everything needed for the IH in one neat package that can be rolled around the shop & stored easily when not being used.

I'm scrounging around now for some wire & switches to finish it up next weekend & if it works I'll post up some pics & maybe a video.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on April 01, 2019, 04:02:35 AM
^Looks like everybody's got different struggles=)
So over the weekend, I put everything together and it works... (numbers in my previous post were completely nonsensical due to me forgetting about RMS vs Pk thing). I was confused, but hopefully not anymore. 

The torus has 184 wire turns which makes it about under 1V per turn. It was converted into a regular transformer, tapped on 54th coil which gave the correct 50 V when made DC (idle). I hooked up the unit and the voltage dropped to about 38V at 6 amps. I have put bolts and coins in the coil. They do heat up to orange glow. Small Items seem to draw no more than 10 amps.
I also inserted a graphite crucible which draws larger current and voltage drops to 20V.
Fans seem to be alright, and are rated for 24 V by the way.

Next steps would be - getting a larger, longer coil to go around the whole crucible. I think I might go for proper switching power supply since I found a good deal on ebay.
I cannot understand why transformer voltage drops so much with even small-ish current - what I read on the internet regarding transformers' voltage regulation issue sounds a bit contradictory. It should be no more than 5% and that is only when transformer is saturated. Definitely not the case in my case.

Pictures attached=)
(https://highvoltageforum.net/proxy.php?request=http%3A%2F%2F%5Battachment%3D1%5D%5B%2Fattachment%5D&hash=7d3863697bff2aa03c77da79c8bd8fde)
(https://highvoltageforum.net/proxy.php?request=http%3A%2F%2F%5Battachment%3D2%5D%5B%2Fattachment%5D&hash=d33011d10dd2c9efe6c9b46d981baab2)


 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on April 01, 2019, 04:08:02 AM
Glas to see that things are coming along, DICKEYBIRD.

For what it's worth,  I just uploaded my next, and possibly last video about my adventures with the 2500 Watt ZVS Induction Heater.
It is here:
/>
Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: DICKEYBIRD on April 01, 2019, 09:03:01 PM
Great video Pete, thanks for posting!  From what you've discovered so far, do you think  it's possible to heat smaller pieces to high temps without making a smaller work coil?  Or do smaller pieces just take longer with less power?  The intended use of my 1800W unit is the hardening of O-1 tool steel stock -  (approx. 1/4" to 1/2" dia, 1" to 2" long)  Maybe a "focusing" coil or device to position inside the existing coil? 

Again, thanks for your enlightening videos!
Milton
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on April 01, 2019, 10:20:41 PM
Re: Heat treating small pieces pf O1 tool steel:
I think pieces as small as you describe can easily be heated to the required temperature:
"Heat Treatment. The heat treatment requires O1 steels to be slowly preheated to 649°C (1200°F) and then heated at 788-816°C (1450-1500°F). Then these steels should be held at the same temperature for 10 to 30 minutes and finally oil quenched."

That temperature is just about the curie point anyway, so current should not be dropping much.  Note the pre-heat conditions, too.
As far as the time at temperature, as you probably know, this relates to getting the heat all the way to the center of the material.  So, with pieces as small as you mention, you'd only need a couple of minutes to do the job.
  Another way to handle pieces that require higher temps is to put them into an insulated graphite crucible  You should have no trouble getting over 2000°F  with steel that way.  In one of my 1000 watt videos. I get a few hundred grams of 1" diameter steel to over 1200°C by insulating below, the sides, and above the work coil.
  So, there are many "ways to skin the cat".

These comments are from a practitioner (me). not from a scientist.  Curie point varies with carbon content and with content of other metallic alloys.   Required hardening temperatures vary, too, with alloy levels.
 
 i have even considered using a hollow graphite tube to help concentrate the heat.

Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on April 14, 2019, 12:23:14 AM
New video-   Work piece size versus coil size:
/>These principles apply for all sizes of ZVS induction heaters, as far as I know.

Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: DICKEYBIRD on April 14, 2019, 03:58:34 AM
Very informative video Pete; thanks for taking the time to put it together & post it!  I'm itching to get mine going but unfortunately I haven't had time to work on it much lately.  A neighbor brought me a some more machining jobs to do for his company in my spare time.  The ol' hobby machine shop can always use the influx of cash!

Where did you find the braided fiberglass sleeve you have on your work coil?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on April 14, 2019, 03:00:18 PM
Fiberglass sleeving:
https://www.ebay.com/itm/1meter-Manhattan-F240-2AWG-6-68mm-240-C-Fiberglass-high-temperature-sleeving/161643155584?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

They sell it my the meter.  I usually buy 3 meters at a time and, so far, they send me one whole 3 meter length.  Which is a good thing.
In the past, I have used 6mm sleeving instead of that 6.68mm stuff, but it's a bit harder to thread onto the  1/4" tubing that I use for coils.
If you look for "high temperature fiberglass sleeving" you will get lots of choices.

By the way, I have written and "filmed" lots of stuff for the 1000 watt ZVS induction heater that relates to the 1800 watt and 2500 watt models.
Go here to see it:
https://spaco.org/Blacksmithing/ZVSInductionHeater/1000WattZVSInductionHeaterNotes.htm

Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on April 16, 2019, 01:20:34 AM
I just assembled an Excel spreadsheet of data about the latest induction coil power transfer video, along with some data from earlier tests.  I am sure to add to this spreadsheet as new information dictates.  It is probably not the best presentation of the data, but I try graphing the results in a few different ways to make some sense of it.
It is here"
https://www.spaco.org/Blacksmithing/ZVSInductionHeater/ZVS2500Watt/Work Coil current and frequency change with size and shape of material.xlsx (https://www.spaco.org/Blacksmithing/ZVSInductionHeater/ZVS2500Watt/Work Coil current and frequency change with size and shape of material.xlsx)

Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: DICKEYBIRD on April 18, 2019, 04:32:55 PM
Thank you Pete; I have some on the way now.  That should check one more thing off the list of magic smoke releasers on this project! ;)
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on April 18, 2019, 10:13:06 PM
Great video and excel sheet Pete, thank you for sharing. I also have some fiberglass hose in the mail, however long its going to take from China, but then I will box up the heater with the 3 server power supplies.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on April 22, 2019, 04:07:07 AM
I finally made something that works...
Here is my somewhat new setup with all previous mistakes accounted  for (I had no idea what I was doing previously, hope that has changed haha)
a.k.a the guide to using unregulated power supply for maximum benefit!

1. I moved all my operations to my bench connecting directly to the stove outlet via a proper thick cable for high amps.
2.I finally found the sweet spot where to tap the transformer accounting for voltage sag. The idea is to overvolt it just enough so that when the unit is connected to IDLE coil voltage drops to fifty volts (the voltage that the unit is rated for).
3. While doing so, I burned both 24v fans, so now I am using external fans from a pc PS.
4. I managed to melt aluminium in about 50 mins, with a power output between 1700 to 1500 w, using my diy kiln enclosure from another project, for heat insulation. I can measure the power with ac meter from ebay which is super handy. It can only be used on the transformer AC side. Still waiting for shunt dc meter to arrive for unit -side measurements.
5. The setup is stable and nothing is too hot. The transformer is output is taken as two secondaries connected in parallel, sent to a pair of fifty-amp rectifier bridges, with heatsink immersed in water.   
6. I made a couple new coils. The five turn work coil makes the unit run between 40-50 kHz, as it is seen on the oscilloscope. As I understand, smaller coil means higher current, higher frequency of oscillation and potential higher energy draw.

I think I can finally do copper and cast something useful when the THERMAL blanket and the sleeve arrives.

(https://highvoltageforum.net/proxy.php?request=http%3A%2F%2F%5Battachment%3D1%5D%5B%2Fattachment%5D&hash=7d3863697bff2aa03c77da79c8bd8fde)

(https://highvoltageforum.net/proxy.php?request=http%3A%2F%2F%5Battachment%3D2%5D%5B%2Fattachment%5D&hash=d33011d10dd2c9efe6c9b46d981baab2)

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on April 23, 2019, 02:55:40 AM
It's good to see that you have your system working, badpeter.
   I still think I will get some linear power supplies going one of these days.

Over the last few days, I have been preparing a copper melting video and I finally, just today, got it up on youtube.
It is here:
/>

We may be able to compare results when you get your DC current meter.  I think you should monitor DC voltage too.

I suggest that you monitor Mosfet gate signals carefully as you use "smaller" coils that increase tank circuit frequency substantially.  I think you will see that the gate signals round over more as the frequency goes beyond some certain point. This means that the Mosfets are spending more of their "on" time in the linear region which is a very bad thing.  Yes, this condition will cause more current to flow, but that extra current will be heating the Mosfets not the work.  Also, since you are using a linear power supply, you may see the voltage drop well below that 50 volts as you increase the load.  This in itself has a negative effect on the gate signals.
 See the December 8, 2016 entry that is about half way down this page:
http://spaco.org/Blacksmithing/ZVSInductionHeater/1000WattZVSInductionHeaterNotes.htm

Pete Stanaitis
---------------


It is Here:
 
/>
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: DICKEYBIRD on April 24, 2019, 05:24:05 AM
One comment & one question please:

1) For anyone that's building a power supply using 3 or 4 of the HP server PS's like Mads showed in his video...go ahead & isolate all of them as he did.  I read on a couple posts elsewhere that it's a good idea to leave one of them unmodified.  I tried that & it didn't work.  The last one in the series would initially turn on then shut down after a few seconds.  I then did the isolation mod & all is good.  Whew, no magic smoke was released!

2) Question:  Since there is an excess of power available with the 3 (or 4) x 750W PS's, would it be OK  to run my radiator 12v cooling fans and water pump from one of them?  I haven't measured the total power usage but I'm thinking about .5A total for the 2 fans & maybe 1 to 3A for the w/s washer pump I'm using.  Is it unwise to do it that way?  A noob question for sure! :-[
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on April 25, 2019, 04:57:18 PM
Mads-  You mentioned that you will soon "package" your induction heater.  I will be looking forward to the method you use.
Just recently, I see that the Chinese seem to be stepping up their game with the 1000, 1800 and 2500 watt ZVS induction heaters:
https://www.ebay.com/i/163558914286?rt=nc&var=462944781862&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D20160908110712%26meid%3D521ef284b2c7416bb345b6aa93d150c5%26pid%3D100677%26rk%3D6%26rkt%3D19%26sd%3D163558914286%26itm%3D462944781862

They appear to be simply packaging the parts into a nice looking box, and maybe adding a DC SSR?

The price of these units is about half the price (or more in some cases) of the LH-15A  7.5 KW Induction heater that is being sold by many vendors:
https://www.ebay.com/itm/15KW-30-100-KHz-High-Frequency-Induction-Heater-Furnace-LH-15A-110-V/182826308639?epid=17031092066&hash=item2a914c141f:g:nYUAAOSw9TdZ4A~z
By the way, this one is the lowest priced unit I have seen.  There is one caveat----  you need a TIG welder type of water cooler for it.

dickeybird:
Regarding your question about using "excess" power to run your fans and pump---       I suppose that would work, but I prefer to take the load off of the power supply. 
  It is all too easy to stick something into the work coil that causes a high current flow.  If you watched my recent 2500 watt videos, you may notice that at least once I inadvertently mentioned the current going over 50 amps when I put a large piece of pipe to far  into the work coil.
  Of course you will need to get a buck converter if you do use the heater's power supply if your fans or pump run at lower voltages.  In my case, so far at least, my fans and pumps all run at 12 volts so one 3 amp buck converter or one external power source may work well.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 01, 2019, 09:05:38 PM
 Congrats on the successful melt!  I saw another individual on YouTube melt about 1.5 pounds in approximately 20 minutes using 1600 watts and a similar setup.  He gives little if any info so not sure about any details of his test.  That is about the same time it takes me to melt same amount using my small DIY gas fired foundry furnace.  Do you think your melt times would be similar if you did 1.5 pounds?  If you can poor 1/2 pound of copper after 7 minutes and if melting charge time is proportional then about 20 minutes would be a good estimate?   Thank you for all the info you have put out there.  Good to know that the scientific method still exists - great stuff.

Just had another thought.  The 2500 watt units are so cheap now maybe we could buy two, then rearrange the coils on each such that they both wrap around one crucible thereby theoretically doubling the power- your thoughts?  Not an engineer, more of a DIY idea-type guy.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 02, 2019, 05:10:31 PM
Re: "---time to melt 1.5 pounds of copper----in 20 minutes?---":
I don't know for sure, but I think it would not take the whole 20 minutes because part of the time is taken up by heating the crucible itself.  But I don't know exactly how it would go, since 1.5 pounds of molten copper  would pretty much fill that crucible right to the top.  As you can see, I filled the crucible as full as I could get it and it melted down to only about 1/3 the depth of the crucible.  That means that I'd have to continually add bits of copper as it melts.  That could make things worse because I'd be uncovering the crucible more often, but it might be better because the unmelted bits of copper might keep the current up a but higher.

Re: doubling the 2500 watt heaters:
I have been asked that question before.  Personally, I don't think it would work.  I'd be afraid that the magnetic fields would interact in a bad way.  But, maybe they would sync up together?
One other issue is that you would still have to obtain an additional power supply, cooling system, etc..

I hope that some of the smart HV/Tesla guys on this forum will comment on this.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on May 02, 2019, 09:57:40 PM
Mads-  You mentioned that you will soon "package" your induction heater.  I will be looking forward to the method you use.
Just recently, I see that the Chinese seem to be stepping up their game with the 1000, 1800 and 2500 watt ZVS induction heaters:
https://www.ebay.com/i/163558914286?rt=nc&var=462944781862&_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D20160908110712%26meid%3D521ef284b2c7416bb345b6aa93d150c5%26pid%3D100677%26rk%3D6%26rkt%3D19%26sd%3D163558914286%26itm%3D462944781862

They appear to be simply packaging the parts into a nice looking box, and maybe adding a DC SSR?

The price of these units is about half the price (or more in some cases) of the LH-15A  7.5 KW Induction heater that is being sold by many vendors:
https://www.ebay.com/itm/15KW-30-100-KHz-High-Frequency-Induction-Heater-Furnace-LH-15A-110-V/182826308639?epid=17031092066&hash=item2a914c141f:g:nYUAAOSw9TdZ4A~z
By the way, this one is the lowest priced unit I have seen.  There is one caveat----  you need a TIG welder type of water cooler for it.

I will reuse a old cabinet and other stuff I already got in my workshop, I will see what I can house it in, without buying any new parts, recycling for the future!

That is indeed getting cheap for boxed heaters with warranty, it is almost like they want everyone to own one :)

Just had another thought.  The 2500 watt units are so cheap now maybe we could buy two, then rearrange the coils on each such that they both wrap around one crucible thereby theoretically doubling the power- your thoughts?  Not an engineer, more of a DIY idea-type guy.

The issues here would be proximity heating between the two coils, that they simple induction heat each-other and they would properly interact on each-other in a destructive way if they are out of phase from running different frequencies. I am not too sure on this, but I doubt it will end up well with so little control over the switching that we have in a Royer oscillator.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 03, 2019, 04:20:42 PM
Do you think we will ever see them make a 4k bare bones unit?  I see they have a 6k unit in fancy box with overload, meters and pump (no power supply) for $900 shipped, but as far as I know no one has tested it yet.  maybe because it would overload many people's homes?

DIY version:

/>
I want that.  array of big caps may be a better method, though more expensive probably. 

this MIT EE student gives a bill of materials and an unreadable schematic for a 3k with some good tips:
https://www.instructables.com/id/30-kVA-Induction-Heater/
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: shortyg83 on May 03, 2019, 09:37:49 PM
Glad I found this post it has a lot of useful information.
I ordered the 2000W ZVS model. It should arrive today.
It has a built in display that will read voltages, temps etc. And says it has protection built into the unit.
I bought it was a power supply that works on 120v or 240v. I live in the USA so for 240V I will have to hook the power supply up via split voltage, which should be the same as single phase 240 in other countries.
I will report back with some results once I get some testing done.

https://www.ebay.com/itm/ZVS-Induction-Heater-Heating-2000W-45A-Module-Power-Supply-3000W/273107970557?epid=11016480565&hash=item3f9680e9fd:g:A4MAAOSwG1Vb7Nvk
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 06, 2019, 10:43:50 PM
Interesting 2000 watt ZVS induction heater module.
I see that "they" are producing many new variations lately.
It's nice that this one has the LCD readout for several variables.
"Protection" has to be a big plus.  It is great that the system can tell you which Mosfet has failed.
I am a bit surprised to see that it has only one fan and that the fan doesn't blow on the capacitors that are closest to the work coil.
I also note that the capacitors in the video linked on the item's "for sale" page are very different from the ones shown in the item link itself.
Lastly, I wonder why the bolt in the work coil didn't seem to glow during that 5 minute video.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: shortyg83 on May 06, 2019, 11:39:34 PM
I made a quick video just to see if it worked before the final setup.
It heated up a knife I am making from an old file in just a few seconds glowing red.
The video on the ebay listing is before they changed the device. The ones they are selling now look like the same from the ebay pictures and from the video I am linking.
I have no idea how the bolt didn't glow. I see in the sellers video the screen never reads more than 550Watts. It could be the bolt was too small or didn't contain the right metal content.
In my first test it got up to over 1400w pretty quickly and the metal was glowing. I will make more videos once I get everything in better posistion.

I will not that I need a bigger water container. Even in my quick video the water running through the coil got quite warm so I want to get a tank that holds at least 1 gallon of distilled water.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 07, 2019, 12:54:12 AM
Great first demo!

It sure did heat that blade!
Looks like you have a good start toward a nice enclosure.

  I use radiators with fans to keep the water cool.  We have a local on-line auction house that has various kinds of radiators from time to time so I get then pretty cheap.  An old automobile interior heater should do a good job.
I did some real basic calculations on water heating:
            
How much will the water heat up?            
assume an idle current of         6   amps
Assume half goes to the coil         3   amps and the other half goes to Mosfets, caps, etc.
   power supply volts      48   
      Watts   144   
   Btus @ 3.4/ watt      489.6   
            
            
One btu raises the temperature of one pound of water one degree F            
One gallon of water weighs ~         8   pounds
Temp F rise per hour, degrees:         61.2   with NO load.  (No heat loss to the surrounding area)

The current distribution is just a guess, but just to have some idea.
You probably know this, but it is important that your cooling water goes INTO the bottom of the coil and comes out the top.
I have boiled water more that once by getting this wrong!

Pleae let me know if I got the calcs.  wrong.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: shortyg83 on May 07, 2019, 04:50:37 AM
Great first demo!

It sure did heat that blade!
Looks like you have a good start toward a nice enclosure.

  I use radiators with fans to keep the water cool.  We have a local on-line auction house that has various kinds of radiators from time to time so I get then pretty cheap.  An old automobile interior heater should do a good job.
I did some real basic calculations on water heating:
            
How much will the water heat up?            
assume an idle current of         6   amps
Assume half goes to the coil         3   amps and the other half goes to Mosfets, caps, etc.
   power supply volts      48   
      Watts   144   
   Btus @ 3.4/ watt      489.6   
            
            
One btu raises the temperature of one pound of water one degree F            
One gallon of water weighs ~         8   pounds
Temp F rise per hour, degrees:         61.2   with NO load.  (No heat loss to the surrounding area)

The current distribution is just a guess, but just to have some idea.
You probably know this, but it is important that your cooling water goes INTO the bottom of the coil and comes out the top.
I have boiled water more that once by getting this wrong!

Pleae let me know if I got the calcs.  wrong.

Just out of curiosity how would the direction of water flow through the coil change how well the water cools? Is it so any steam that may exist escapes upwards?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on May 07, 2019, 10:59:10 AM
I want that.  array of big caps may be a better method, though more expensive probably. 

I got some large induction heater caps for sale, real bargain to the size of them :)

https://highvoltageforum.net/index.php?topic=56.0
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 07, 2019, 02:45:24 PM
Re:Just out of curiosity how would the direction of water flow through the coil change how well the water cools? Is it so any steam that may exist escapes upwards?
Answer: If the water flows into the top of the coil. it can simply run down to the bottom coil and out to the "drain" without filling the coils.   When I change coils, I have to get all the bubbles out.  This flow orientation also helps to get ALL the bobbles out of the system before I turn the power on.
I did this wrong on one of my earlier "1000 watt" videos and you could see steam and water jumping out of my radiator's expansion tube. 
The MAIN idea is to eliminate the possibility of any steam forming in the first place due to an incompletely filled coil.

Mads:  Please remind  about the specs and prices for your capacitors----
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: DICKEYBIRD on May 07, 2019, 05:22:14 PM
Great info, thanks all!  Never even considered the water direction issue; thanks Pete.  Due to enclosure space issues, I'm using a 1 qt. distilled water tank for the aluminum auto heater core fitted with 2, 12V muffin fans and a water pump.  I'm hoping that will be enough but if it isn't, I'll add an additional external 1 gallon tank.

I'm using this cool little thermostat to read coolant temp & switch on the fans when needed: https://www.amazon.com/gp/product/B019I3YCFS/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1 This speed control for the pump: https://www.amazon.com/gp/product/B007TH4EN6/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1 and this "wattmeter" to monitor power: https://www.amazon.com/gp/product/B0753DPC2D/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on May 07, 2019, 07:58:39 PM
^wow so much activity here!
Well, I managed to melt my first copper! so yay...
I rebuilt the PS with a powerful fan underneath, using the original box. It looks very neat.
But most importantly, insulation does miracles.

The data is the following:
845 g of copper melt in a graphite crucible (so-called "3kg-crucible" on ebay)
in about an hour with an output of just under 1kW.

the question is, how do I draw more power? I cant make the coil any smaller because of crucible+insulation being quite thick. I can have more turns. I was thinking, what if I do TWO coils, meshed together (not touching), turned the same direction.
Would that double the drawn power(some sort of principle of superposition)?

I plan to make aluminium bronze and cast a nice golden-looking dagger=)

Here are some pics:   
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: shortyg83 on May 07, 2019, 09:14:05 PM
So for some reason certain types of metal appear to be causing the induction heater to draw to much power and go into a protect mode. It is a 2000w heater but I am using a 3000W power supply and I was assuming it would only draw up to 2000W. But I put a piece of 440C bar stock in and if I move the bar through the coil at a certain speed where say length that is currently in the coil hasn't been heated at all yet the heater starts drawing 2200 then 2300 Watts and ends up going into protect somewhere just over 2300W. If I move the bar stock through slowly where it has time to heat smaller sections at a time it works fine.

Is there anyway for me to limit the power from my power supply where it can only goto say 2200 or so watts? It currently outputs 53.5V at 56.1 A DC.

The heater is 24v-65V with a max Current of 48Amps. I don't think these heaters like being run below 48V though.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 07, 2019, 10:15:30 PM
badpeter:
  You need thinner insulation so you can make a coil the more closely fits the crucible.
Like this:
https://www.ebay.com/itm/INSWOOL-2300-PAPER-Flexible-Refractory-Paper-1-8-x-50-partial-rolls-also/131815404577?hash=item1eb0cf7421:m:m03iqra7mYUl9GLx0gPJ9rA
 what is your Idle current with that coil?  I see that the turns are pretty far apart.  That should reduce its inductance and make it run at  a higher frequency which may not be helpful, since you are primarily heating graphite, not copper.   You may also have a higher idle current so the net current for power transfer to the load will be less.
It appears that you are only heating about half the crucible.  That can't be helpful, can it?   Why use a 3 kg crucible and not a one or two kg crucible? Or get one that is already insulated with a hard ceramic shell such as the one you have seen my use.

I think everyone who get serious about this stuff should invest in an LC meter like this one which costs USD$10.00:
https://www.aliexpress.com/item/Digital-LCD-Capacitance-meter-inductance-table-TESTER-LC-Meter-Frequency-1pF-100mF-1uH-100H-LC100-A/32829243371.html
Then you can make coils and be able to predict how well they will work, while not overtaxing your heater.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 07, 2019, 10:30:58 PM
shortyg83:
"for some reason---":  The reason is that various alloys suck up more power than other do.  Shapes that fit the work coil more closely also tend to soak up more power.  That's usually a good thing-----  more power transfer!
  No individual coil works for everything.  If you are serious about these devices, you will have to learn how to make coils to match the work.  Many of my earlier videos show these effects.
  Usually, ferrous metals (those containing iron) soak up more power than do non-ferrous metals.  That is true up to the point where they start to glow a medium red color, where, by the way, they also become non-magnetic.  This is called the "transformation temperature" or "Curie Point".  At that temperature, one of the major factors that makes them heat, goes away.  That's due to the cessation of hysteresis as the magnetic property diminishes.  You saw that effect as you moved the stainless steel piece through the work coil.  (440C contains approx.  82% iron and the rest is alloys).

Link to youtube channel videos for the 1000 watt heater which has several relevant videos:
https://www.youtube.com/playlist?list=PLVxWen9M87dBhvInCQ-3pELWdxCM3XH4I

Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 07, 2019, 11:38:21 PM
Would insulation on the outside of coil rather than inside be better?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on May 07, 2019, 11:51:20 PM
Peterspaco:
I might try the thinner insulation, but the one I have is quite amazing. May be losing some efficiency with a thinner one.
Idle current: looks like i forgot to record it with the latest setup. will have to get back with that.
Crucible wrapping is one thing i didnt think of. Will try that next!
I hope to cast bigger things so even a 3kg crucible is too small. I made a whole sword with aluminium when I ran my propane mini kiln!

 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on May 07, 2019, 11:55:50 PM
hightemp:
If insulation is outside then water will definitely boil in the coil not to mention that the water be stealing a lot of useful heat away. The previous setup with bricks was somewhat like that, before I had the fiber insulation
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: shortyg83 on May 08, 2019, 01:24:14 AM
hightemp:
If insulation is outside then water will definitely boil in the coil not to mention that the water be stealing a lot of useful heat away. The previous setup with bricks was somewhat like that, before I had the fiber insulation

They make crucibles that come with ceremic sleeve insulation so you don't have to use all that. You can probably find one to fit your coil.

https://www.ebay.com/itm/Induction-Melting-Furnace-Graphite-Crucible-with-Ceramic-Shield/273657494243?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649&fbclid=IwAR0jaVvHhOtCpPofcWgwc7rDLkak0ZXkLETXEp42kzXw-Gjk7o_rHoHgLv4
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 09, 2019, 05:31:34 PM
Annealing Brass Cartridge Casings with a short (2- layer X 3 Turn) coil:
I just put this video on youtube last night:
/>
Many ammunition "reloader" guys ask about this, so I thought I'd try a coil design that might work.  (I am not a relaoder guy),  I see that some already do use these small induction heaters to do this task, but I am not sure they are running their systems in a sustainable way.
So my focus is to make sure that Mosfet gates turn on rapidly by using coil designs that keep the oscillation frequency to  acceptable (upper) limits.
 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 09, 2019, 08:09:24 PM
Peterspaco:
I hope to cast bigger things so even a 3kg crucible is too small. I made a whole sword with aluminium when I ran my propane mini kiln!

badpeter, keep up the good work, very curious to know how much copper you will be able to melt.  I am also interested in melting larger quantities (1-5 lbs esp.) knifes, swords, parts, etc.  but have not yet purchased this 2500W unit because AFAIK no one else has reported that they can melt more than 500 grams, at lest repeatedly.  So probably this design just does not have enough power to melt larger quantities (maybe it can melt a pound or two max if tweaked properly?)  Peterspaco has the best tests and has confirmed repeatable 500 kilogram melts with excellent results.  I'm hoping that someone shows what the practical limit of the melt size is, especially for copper casting alloys.  Obviously at some weight,  it will not melt a given quantity no matter how long you run it, and if takes too long (say 1 hour?) then the metal will probably pick up too much oxygen causing porisity, etc.   Will it melt 1,2, 3 lbs. in 15 minutes, 30 min, 60, never... ?   Peterspaco total power output is only approx 1600 watts when melting copper so we are already close to maxing out the power.  There is some headroom there - approx 700W that is still available - however this power is not being used because this unit can not output anymore amps to the crucible/copper load.  Possibly, if the crucible was a heavier gauge steal then it might utilize unit's full 2500 Watts, however, I don't think that you would ever want to melt copper in steal because it would absorb way too much iron causing embrittlement, poor properties.  I know very little about induction heating so tweaking the board to run hotter (larger caps,etc.) is beyond me.  For all I know it is not even possible or if so, prohibitively expensive.   
   We do have other alternatives.  Larger, though much more expensive induction furnace.  I did contact a regular industrial supplier of induction furnaces here in the states and was quoted $5000 for their smallest unit that can melt 4-6 lbs of copper in 5 minutes).  When I said that was way out of my budget he basically hung up on me.  Though he did say theirs are built way better.  A custom sized DIY propane/gas furnace will easily melt 5-30 pounds.  Resistance furnace is another option. Those 2-3 kilo gold/silver melting units that sell for about $300 - however I wonder if they are also under-powered for melting more than even a kilo or two of copper?   The thing that draws me to both electric induction and electric resistance melting is the noise factor - not bothering my nice neighbors.  Another possibility is some type of custom DIY arc furnace.  An arc type furnace may actually be the most efficient and quickest method for my size melts, though again the commercial units are prohibitive and there is even less DIY info on them.   Eventually, I will decide on probably one of these three electrical methods.  With limited electronic knowledge and resources the decision for me will boil down to good proven info from DIY sources and of course economics.  Opinions on the best electric method for small size melts of 1 to 5 lb size melts?

Arc, Induction, or Resistance???
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 10, 2019, 05:13:21 AM
I just tried melting some more copper with the 2500 watt unit.
It went well despite my making a newby mistake by putting to much cold metal into the molten copper in the crucible.
The video is here:
/>
Interestingly, the current dropped more than in previous melts as the copper first melted.  I think I have some ideas about that, which will require further testing, one of these days,  But, even at 24 gross amps, (18 amps net) and 48 volts or (864 watts),  the full  crucible sure did melt well.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on May 10, 2019, 04:16:15 PM
Hightemp:
Well, the way I see it, power output will determine how quickly you heat things up and WHERE the thermal equilibrium is reached - aka power IN starts being equal power OUT.
It is also determined by losses. Even if energy is pumped in at a slower rate, but you somehow can magically improve insulation, you will reach equilibrium at higher temperatures. The other thing to note is, exponentially more energy is required to raise something to a degree at higher temperatures than at lower temperatures (relative to outside temp that is). That fact was especially evident with my other-other pottery kiln which lights up an LED when SSR is on so it is easy to see the difference.

You can reliably melt about 3 kg s of copper with about 800 W. I will be doing further tests + casting via lost PLA method soon ish, will have real numbers. It is funny how i started thinking like a scrapper a bit - always checking if there is some copper laying around somewhere haha.
peterspaco: I nearly doubled the coil so it covers full crucible. Power stayed nearly the same, even decreased a bit. Frequency has halved. I think the only way to increase output is to change diameter that can't be done currently with my setup.
To kind of summarize it (correct me if i am wrong) but MORE power is drawn if we have:
Lesser coil diameter
More material inside the working volume
Higher frequency
Less turns in the coil

 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 10, 2019, 11:51:23 PM
I just tried melting some more copper with the 2500 watt unit.
It went well despite my making a newby mistake by putting to much cold metal into the molten copper in the crucible.
The video is here:
/>
Interestingly, the current dropped more than in previous melts as the copper first melted.  I think I have some ideas about that, which will require further testing, one of these days,  But, even at 24 gross amps, (18 amps net) and 48 volts or (864 watts),  the full  crucible sure did melt well.

Congrats - Job Well Done - Thank you so much, you are the best !!   That was a significant amperage drop compared to the last melt, approximately 30% net amps drop, at least towards the end (18 net vs 26 net amps).  The only difference is the extra charge, I think (9 ounces vs 18 ounces)?      It is confusing why these units can not maintain amperage throughout the melt.  I'd almost think that with the crucible filling with metal that the amperage would if anything go up, but then again, induction heating is mostly Greek to me.   badpeter is going to be doing some similar size melts and casting in molds, so his tests may confirm this, if they have not already?  Great stuff guys - love it!   Foundry fumes can be nasty so if you don't already have some kind of exhaust system, you may want to add one.  I use a simple box fan cranked on high with same size heppa filter attached to the back.

Correction: Not sure, but I think brass shot would be a better "thinner" than pure zinc since zinc would instantly vaporize at copper melt temps.  Brass shot would give off a lot of zinc fumes as well but might have a better chance mixing if "dunked" under the melt.  Aluminum bronze is being used for swords and such cause it is one of the strongest copper alloys even without high tech heat treatment.  But the ratios need to be more precise and may be more difficult to cast because of shrinkage.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: flyrod on May 11, 2019, 04:59:43 PM
Annealing Brass Cartridge Casings with a short (2- layer X 3 Turn) coil:


Thanks for sharing your results.  This is my version for annealing brass:



This is off topic, but to whom it may concern:  I'm having difficulty with this site.  I get a lot of 403 errors when clicking on links.  I can get 2-3 page loads before I get blocked.  I can still load pages through a proxy, but then I can't post.  To post I have to remember what I wanted to post from the previous day and do that first, after a couple attempts because "Your session timed out while posting. Please try to re-submit your message." For me, this really detracts from the experience...
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on May 11, 2019, 08:34:31 PM
Mads:  Please remind  about the specs and prices for your capacitors----

100$ each or we can make a deal if you can use more than one.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 12, 2019, 12:18:58 AM
Flyrod:
Looks like you have the process well in control!

How far down the casing does the anneal go?  ( I have heard that you don't want to go any farther than the just the neck).
I'd think you'd want to quench in water, but I guess many folks do as you do. 

How about some numbers:
-System power capability
-Net Current to the work
-Temperature (I see things glow a LOT, but with white balance problems being what they are, I can't tell.)  What temp ARE you aiming for?
-Frequency

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 14, 2019, 06:05:25 PM
^wow so much activity here!
Well, I managed to melt my first copper! so yay...
I rebuilt the PS with a powerful fan underneath, using the original box. It looks very neat.
But most importantly, insulation does miracles.

The data is the following:
845 g of copper melt in a graphite crucible (so-called "3kg-crucible" on ebay)
in about an hour with an output of just under 1kW.

the question is, how do I draw more power?


Badpeter, any luck on getting more power?  Wonder what would happen if you added another one of the donut things and put in parallel?   The extra 500 or so watts may greatly reduce your melt times and the metal may be cleaner - less time to pick up oxygen, dross, etc.   Petespaco gets between 32 and 38 amps when melting about 9 ounces, however on the last larger 1.2 lb copper melt test the amp output dropped all the way to 26 amps or 1250 watts, after all the metal was added. 
  I have not yet decided on a PS.  Possibly a MOT rated at 1250 Watts or more.  At 50 volts that is about 25 amps.  Problem is getting 60 turns when manually rewinding magnetic wire that is heavy enough to handle say 32 amps all day long.  Petespaco amazingly got about 41 turns producing 31 volts on a small test MOT here on YouTube.
 Potential problems deal mostly with rewinding - choosing correct wire gauge (ie single a 14 gauge wrap or ganging multiple gauges in parallel, say three 18 gauges together, also scaring the wire while wrapping and expense of magnetic wire. Curious, how much did you pay for those donuts?   Anyhow, hope that you eventually show us some more of your bigger melts and some cool castings. 

NOTE:  My MOT ideas are based on assumption the 2500 ZVS works best at 48 voilts.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on May 14, 2019, 07:41:48 PM
Hightemp: I think the only way to get more power is lesser-diameter coil and more material/graphite in that diameter. I don't think I can alter my current setup much anymore.
My donut is using two secondaries in paralel to help with distributing high current over twice the wire as well as for cooling reasons (more turns take up more area of the donut). Adding things in paralel will do nothing. To draw more power - something has to consume it (aka work piece). It cannot be forced.
I have made some ingot molds outta plaster+sand (50/50) as well as a mold for a british ww2 thin dagger off a 3D printed piece from Thingiverse. I also printed a sphinx figurine to test out lost PLA method. When i did that, someone suggested purchasing a roll of water soluble PVA filament and just use that to print with! that be so much simpler.
Re power supply, I see that ebay has so much more to offer now! I would've never gone with the donut if these options were available for a comparable price for high power regulated psu (around 90$). the diy donut transformer journey was a long one and I do not recommend it.

Re MOT - seeing how transformers drop a lot in voltage when connected to load, I overvolted mine when load free such that when idle zvs is connected voltage drops back to around 55 volts. (overvolt was on the order of 15 V or so - quite a bit). This killed the fans by the way, connect them to external supply if you go that way). 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 14, 2019, 08:35:28 PM
 I am amazed that you melted almost 2 pounds (845 grams) on less than 1000 watts.  Did you have much metal loss, and dross on the 1 hour melt?  I wonder how petespaco's power would drop if he tried 2 pounds on a bigger coil/crucible - maybe similar to yours - or about 1 kilowatt power when fully melted?  What is inside diameter of your coil and crucible's approximate area - or is 6 kilogram capacity for copper or gold?  Thanks for the fan tip on overvoltage for mots.

I did some simple two part plaster casting years ago using metal casting plaster, basically what you are using, sand and plaster.  Make sure to dry them completely, regular kitchen oven works fine.  Pouring when molds are hot 450 degrees helps with mold filling.  Did not try any lost wax casting but the water soluble patterns sound very interesting.  If you can dissolve/drain pattern within mold without loosing pattern detail and without contaminating mold so that high temp burnout is unnecessary then it would simplify the process considerably.  I'd be very interested to know how that turns out for you.  Have you poured the 3-D figurine, or knife molds yet?  Please keep me posted !!

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on May 14, 2019, 09:58:28 PM
There wasnt much dross, copper was clean, mostly from av cables. Coil has a diam of 12 cm and something like 16 turns.
Here is my youtube channel where I melt some aluminium with my other diy propane kiln (sword and ingots in another one). When I finally get to make an induction video will post that on there too.
/>Also, on unrelated note, the epic power plant tour vid may be of interest to high voltage enthusiasts... but thats a different story...
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 14, 2019, 11:28:43 PM
There wasnt much dross, copper was clean, mostly from av cables. Coil has a diam of 12 cm and something like 16 turns.
Here is my youtube channel where I melt some aluminium with my other diy propane kiln (sword and ingots in another one). When I finally get to make an induction video will post that on there too.
/>Also, on unrelated note, the epic power plant tour vid may be of interest to high voltage enthusiasts... but thats a different story...

Thanks for info and for sharing your video.  Sword looks beautiful -congratulations!   I encourage you to finish and put on your mantel.  Possibly to eliminate air holes you need more metal to melt to allow for a riser and/or a gate, not sure though as I have never casted anything that big?  Correction on prior post -you are using a sand type mold, different than the "plaster of paris" type mold I used where you mix equal parts of water to very fine sand/plaster, pour on pattern then let it set so it is rock hard.  I know little about sand casting so don't have any other tips but there are many videos on youtube about sand casting.  Luckygen1001 is one of the better ones to check out.  He does lots of aluminum, bronze, zinc and cast iron with fantastic results.

Wow, you are using huge coils -almost 5 inches and still getting descent power.  That is very interesting as I still have an old salamander graphite crucible about that size -may have to get it out of the moth balls.     If you do 3-D printing those could go hand in hand with these induction melters, giving you an unlimited source of intricate patterns. Most of the patterns I made were machined from wood using basic woodworking tools (drill press, router, etc. - the old fashion way).
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 17, 2019, 10:57:17 PM
hightemp1:
  Just a  couple of small but important corrections:

Quote
however on the last larger 1.2 lb copper melt test the amp output dropped all the way to 26 amps or 1250 watts, after all the metal was added. 

Should read:
however on the last larger 1.2 lb copper melt test the amp output dropped all the way to 18 amps NET, or about 864 watts into the work, AT THE MOMENT THAT THE COPPER MELTED .
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 18, 2019, 10:48:59 PM
I've been doing more with work coil design lately.  I've just published a somewhat lengthy (sorry about that!) youtube video showing me laboriously producing a 2 Layer 3 Turn coil.  Its part of my attempt to heat brass cartridge cases faster, while keeping the ZVS heater board safe and able to run continuously without failure.
Anyway, to make it easier to follow those "exploits", I also just put up a webpage dedicated to the work coils themselves.
It will be updated regularly for the next few months at least.
It's at:
http://www.spaco.org/Blacksmithing/ZVSInductionHeater/WorkCoilsForZVSInductionHeater.htm
Any pertinent coil-related videos will be (and already are) linked to on that page.

Pete Stanaitis
----------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: flyrod on May 19, 2019, 04:04:12 PM
Its part of my attempt to heat brass cartridge cases faster, while keeping the ZVS heater board safe and able to run continuously without failure.

Here is a thread about doing this on a reloading forum:

http://forum.accurateshooter.com/threads/induction-brass-annealer-redux.3908353/

It looks like most of those guys are also using the cheap chineze boards too.  There is not a lot of electronics expertise over there, but they've got things working through trial and error and people sharing their results.

With a better gate control I've been able to run 400kHz without problems.  This works well with small, thin cases in small coils.  The idea is to quickly heat the neck of the case without heating the head.  A small coil allows you to do this, otherwise you just heat the whole case and ruin it.  The neck acts like a gasket, so you want it soft.  The head has to hold the pressure, so you want it hard.  If you soften the head it becomes dangerous because it can "KB" and vent gas and metal particles towards the operator. 

These guys have a commercial induction annealer and a lot of technical info published on their web site on brass hardness, etc. if you want to get into the details:

http://ampannealing.com/



Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 19, 2019, 06:40:41 PM
Yes, I have been to both those sites.  I am certainly not planning to re-invent the wheel, just to understand these particular ZVS units better.

Re:
Quote
With a better gate control I've been able to run 400kHz without problems.  This works well with small, thin cases in small coils.
Believe me, I appreciate the "better gate control" comment.

I have read that the Mosfets we are using are good to at least 1 MegaHz.  So it's the design of the gate ckt in these induction heaters that's the problem.
And I am not about to monkey around with them.
 
What voltages and currents can you handle at 400kHz?
How much net current or power is going into the casings when you anneal them.
You said "small thin cases".  is 7mm small?  What is "big"?
Can you comment on work coil sizes that you use?

As we all know, it is said that higher frequencies work better for transferring power to nonferrous materials.  But, really, how big a difference DOES it make?  For me, I think these heaters could go up to about 115 kHz or 125 kHz or so which could be about a 25% increase from  to ~90 kHz where I am running the 1000 watt unit right now.   But is it worth it?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 20, 2019, 02:57:46 AM
hightemp1:
  Just a  couple of small but important corrections:

Quote
however on the last larger 1.2 lb copper melt test the amp output dropped all the way to 26 amps or 1250 watts, after all the metal was added. 

Should read:
however on the last larger 1.2 lb copper melt test the amp output dropped all the way to 18 amps NET, or about 864 watts into the work, AT THE MOMENT THAT THE COPPER MELTED .

Thanks for correcting/clarifying.  Can you or anyone else explain why the measured amps and power dropped so much from start to finish when melting copper, especially since there is no iron involved?  Seams like the more copper we melt the less power these heaters put out?  Also, can a large amount of copper, say 2 pounds in a crucible, somehow be arranged to get the full 2500 watt rated watt output using these 2500 ZVS heaters and still have enough power to melt a kilo of copper?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 21, 2019, 06:12:18 AM
For hightemp1:

My latest copper melting test video will be up on youtube  in about one hour after this message appears.
Hopefully it suggests that there may be a way to get more copper melted in a reasonable amount of time

It will be here:
/>
Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 21, 2019, 06:12:55 PM
Okay, hightemp1, here's the answer:
https://www.academia.edu/23024259/TRANSIENT_NUMERICAL_ANALYSIS_OF_INDUCTION_HEATING_OF_GRAPHITE_CRUCIBLE_AT_DIFFERENT_FREQUENCY

Just kidding, but this paper has a lot of useful information, especially after most of the mandatory academic math is over with,  at about Figure 4.

The main take-away that I got is that  getting that taller crucible that you mentioned (and, somehow insulating it with a THIN material)  and making a work coil with enough turns to encircle it,  might really help to transfer more power.  This should lower the frequency, which should increase penetration depth, if I got it right.

Again, a caution:  If you do this, you really need to be careful not to overtax the system the first time you try it out.  Insert the crucible slowly into the work coil.   

Let us know how it works out.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 23, 2019, 04:07:17 AM
For hightemp1----
  I am moving your last private message to the "public" area, since I think that most of the issues you bring forth are  of general interest to others.  I hope you don't mind----:
Your latest comments:
[/quote]Regarding melting copper, I seem to recall you really need a lot of power as you do not have the advantage of good heating before reaching curie-point, as there is is no curie-point for copper as its not a ferromagnetic material. So your only hope is lots of insulation to keep the heat in.[/quote]
You are correct.  There is also no "curie point" for graphite.

Call me a Doubting Thomas but .....   Knowing what I know about these heaters I don't want to be the 1st person to try and cast something useful, other than a ingot.  Ingots can and should be cast at lowest temp possible for best results.  Small intricate castings on the other hand require superheat temp of 200 degrees in excess of melt temp, else metal freezes/poor detail, etc.  I assume higher temps are exponentially difficult and that is why no one has tried/succeeded AFAIK.
I have been thinking about this.
I do have several sheathed thermocouple type K temperature meters that are capable of measuring temps up to at least 2200°F.
I have used them for years to measure hearth temperatures for  my woodgas to electricitly projects.
It would be easy to stick one into the molten copper to check temperature.  I would turn power off when I do this so the ferrous material in the T/C sheath wouldn't effect accuracy of the reading.  There is a bit of a concern that the molten copper would "poison" the T/C sheath, but I have a few older ones that I could sacrifice if it's true.
  Once, a long time ago, I sold several hundred sheathed thermocouples  (made by a friend of mine) at a time to Boeing to be used in particular foundry practice.  They dropped the T/C into the molten bath each time they wanted to know the temp.  They'd get one or two sample readings before the sheath melted.
  I don't think we'd have the same problem with copper though.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 23, 2019, 05:51:09 AM
Some of those quotes were from Mads, buy yeah, no problem, I'm grateful again - you're the best!  I've heard many pyrometers are not very accurate at these high temps, but most are consistent so if you have a good pour with proper filling then you can repeat measured temp.  Color tests is also difficult and varies depending on day/night, clouds/sun.  Generally a very bright yellow boarding on white is supposed to be around 2200, I think.  Not sure where one needs eye protection so please know/understand or just use protection if you plan on testing and please be careful with hot metal Pete. 

I'm thinking if these 2500 watt heaters don't cut it for casting bronze, then scaling these up somehow, or using another design that puts out maybe 4 to 10KW - the most my home will handle safely. One of my previous post shows a link with bill of materials for a design that accepted 8-15 KW input, though I did not see a schematic.  The lower range could use 220 volt but the upper ranges needed 3-phase power lines -that would be prohibitively expensive.

Curious too, as to why I don't see people casting smaller aluminum items with these, or at least some of the easier to cast, Zamac zinc alloys.  Just my biased opinoion, but I think everyone should possibly have one of these in the kitchen ;)  Just speculating on copper for now.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 23, 2019, 04:56:10 PM
Don't know much about pryometers, but it may be large in relation to the copper load so preheating it with a torch somehow so that it does not cool the melt too much may help.  Those copper ingots can be easily cut & reused.  You may want to pour the molten metal load into water, this makes copper shot, not sure, but that may be better for next reheating melts.  Manufacturer recommendation of not topping off crucible (75% Max-?) will be safer and probably extend your crucible life?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on May 23, 2019, 09:54:18 PM
I finally got to do the casting yesterday... ;D ;D ;D
So I can confirm that aluminium melts in about 15 minutes and copper indeed takes just an hour (my setup is unchanged from the specs that i mentioned).

Also I found out that 50/50 plaster/sand mold, pre treated in an oven DOES withstand thermal shock and doesn't explode like I worried. Great for ingots and other things. The dagger turned out crappy due to air bubbles - i forgot to make the air holes. I think I can use this mould one more time, although I kind of ruined it getting the piece out.

Now my power got even lower to a ridiculous 570 W (wtf!) I thought hard about it and realized something... crucible is withering away. It is much thinner now. Dont know where all that graphite is going but every firing i get slightly less and less power. This got to be the explanation.
The amount of metal inside seems to not affect power drawn. Looks like the amount of graphite is determining factor.

Now I am hearing people add borax to purify the alloy. Will have to do that for cleaner result.
I recorded my experiments, just got to cut the vid!= )
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 23, 2019, 11:20:08 PM
Badpeter, good stuff - cut that sucker - if you post a descent pic of the casting we might be able to tell exactly why it did not turn out (is surface finish & air bubble similar to last pour)?  Crucibles are by nature disposable especially if you have long melt times, and have lots of dross; also, using same crucible for different alloys can screw up castings easily - how many melts did you get out of it?  I used to cast mostly silicon bronze and it did not require a flux, only a good skimming before pour.  Other copper alloys did require both a flux and a skim, not sure about aluminum, though I heard many just skim and pour, as well.  Also not sure on this either, but borax/fluxes may contribute to shorter crucible life due to their corrosive nature. 

How many volts/amp did you start with on this last pour, how many amps did you finish with, and how much aluminum did you melt? 

I know copper can be melted at 2000 degrees with these, everyone is doing it - just looking for confirmation that the required super-heat temps of 2200 can be obtained with a pound or two of copper using these heaters (call me skeptical).

Update: possibly induction swirling melting action has eroded the soft graphite - no clue here???   Careful you don't get a pot of molten metal somewhere not wanted !!!
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on May 24, 2019, 08:53:50 PM
Finally! :)
The dagger didn't turn out pretty but the rest works okay. Hope it answers some questions!

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 24, 2019, 10:31:35 PM
I would never have believed it, but there it is right before my eyes.  A Kilo (?) of Aluminum Bronze cast in one hour using less than 1KW with these ZVS heaters.  Metal actually looked pretty fluid and did a descent job of filling the mold looking very sword-like - CONGRATULATIONS AND THANK YOU !!!

I am only guessing but here is what may have happened.  Aluminum was not skimmed and produced most  of the dross (prepare AL/Bronze ingots beforehand - they will be cleaner). Dross was not removed before pouring or was incorporated in melt (lower part of casting (blade) was filled with drossy metal because drossy metal is lighter and filled the mold first.  Upper part (handle) actually looks very good.  The air hole on the handle is normal shrinkage occurring at the thickest part (either pour directly at thickest part or have a separate riser there).  Other possible cause of the air hole is a mold breakage or mold halves were not clamped hard enough(did you notice the metal leaking out at the end?) Metal should be melted as quickly as possible so getting a 2500 watt PS or better would speed things up -not sure by how much.  Do you know the composition of the aluminum, I think most people use pure aluminum without other impurities, not sure though.  Wish I could analyse further but my better half is waiting for me.

Pete and others may have questions & suggestions too.  Regarding PS. coil, electronics, etc. they will have to advise, but again, I am amazed the power you got out of it.  Granted, you could have melted that same amount of alloy using gas in about 15 minutes with forced air, but the point as far as I'm concerned is bronze casting can be done with these heaters, or not?   
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 24, 2019, 11:16:04 PM
badpeter:
  I think you did pretty good on that pour, for a first attempt.
But---
  You need a riser that acts like a "mold sprued cup" above your sprue.
https://www.researchgate.net/figure/Sprue-cup-shape-in-casting-mold_fig1_325985131

 This gives you a reservoir for material so it can fill in as the metal starts to freeze.
Also, you need a couple of vents in the top of the mold along its length to let gases out. This will also allow the metal to flow faster to the far end of the mold and reduce the pressure so the mold is a bit less likely to leak.  Finally, when those vents start to fill and/or overflow, you know you've got  enough material.

 With something that (relatively) small, you might need as much as 30 to 40% extra material  to fill that mold sprue cup and to make up for any leaks.

I am no experienced caster, but have done some aluminum, bronze and iron casting, being coached and guided by those who are.

hightemp1: The T/C's that I often use have sheath diameters of about 1/8" and I recommend preheating them with a propane torch just before inserting them into the molten metal for small melts.

OT:   Several friends and I have been doing iron ore to wrought iron smelts on an off for the last 15 years or so.  In this case, only the slag actually melts.

Also, when making blister steel, we toss broken used glass into the crucible.  It melts and sits atop the steel, preventing oxidation.  I think this will work well for copper, but probably not for aluminum bronze, due to its low melting temperature.

---Just a shade tree mechanic, looking on,
Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 25, 2019, 01:38:12 AM
OTH, I did not realize that aluminum bronze had such a low melting point - 1900 F and such a high pouring temp of 2300.   Perhaps the temp was not hot enough to melt all the copper and mix homogeneously so the lower part (blade) was more aluminum and upper was more copper.  The molten metal did look more orange than yellow -what color did it look like to you?  The test ingot looked kinda striped - silver spots and gold spots indicating poor mix of copper and aluminum - did you do any kind or strength or hardness test?  Induction heating is supposed to mix the metal for you - or maybe not and you just had to mix it yourself ?  Have to think about it some more.  ???

Update: Just noticed in your description that you have 12% alum and no iron - I think most aluminum bronze normally contains 1-5 percent iron -   I would think without any iron the melting and pouring temps would go down from 1900 and 2300 making it easier to cast, not sure how much though.  Badpeter, what are all your opinions:

 pouring temp(color),
weight of metal load,
manual skim/stir before pouring or not ,
did it look like there was a lot of mixing of molten metal from the induction currents(some say this mixing can look like boiling),
ingot tests,
cause of problems in handle & blade area,
did metal get hot enough for proper mixing to occur,
using more metal for pouring sprue/risers/vents,
drossy or clean metal ?
 

Forgot to mention that the video itself was very professional - congrats there too.  8) 
Can't wait for Part 2...........



Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on May 25, 2019, 05:06:14 PM
So...
Casting: there were 3 problems with moulds: lack of air holes, difficulty aligning two sides, significant crack between two sides. I will redesign the way the mould is, hopefully 3d print something for the mould to address those issues. Also I hope it can be reusable. Riser can be increased too.
I still have one more test to run with lost PLA method, will see how that turns out.

Metal: It melted completely, but I didn't stir it enough and didn't skim. I think convection doesnt do much.  Will try borax as a lot of people seem to use it. It is weird that if you have 7% Al you get that golden shiny color. Try 15%... and it starts looking like it is all Al, althought most of it is copper! In other words, I have put too much Al in this alloy. resulting alloy is still quite strong though.

Power: something is going on with this! With the same setup, every run has less and less output. I tried a quick melt yesterday, max power decreased by another 100 w. I dont know whats going on except my theory with crucible getting thinner and thinner. Imagine if I could get all 1800 w out of this! I'd be able to melt iron (and add it to my alloy). Will have to wait until new crucible from ebay, if power goes high again, I d say that be the proof. Rather inconvenient that crucibles have such a limited life. I wonder if there are any other options beside graphite... 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 25, 2019, 07:08:23 PM
So...
Casting: there were 3 problems with moulds: lack of air holes, difficulty aligning two sides, significant crack between two sides. I will redesign the way the mould is, hopefully 3d print something for the mould to address those issues. Also I hope it can be reusable. Riser can be increased too.
I still have one more test to run with lost PLA method, will see how that turns out.

Metal: It melted completely, but I didn't stir it enough and didn't skim. I think convection doesnt do much.  Will try borax as a lot of people seem to use it. It is weird that if you have 7% Al you get that golden shiny color. Try 15%... and it starts looking like it is all Al, althought most of it is copper! In other words, I have put too much Al in this alloy. resulting alloy is still quite strong though.

Power: something is going on with this! With the same setup, every run has less and less output. I tried a quick melt yesterday, max power decreased by another 100 w. I dont know whats going on except my theory with crucible getting thinner and thinner. Imagine if I could get all 1800 w out of this! I'd be able to melt iron (and add it to my alloy). Will have to wait until new crucible from ebay, if power goes high again, I d say that be the proof. Rather inconvenient that crucibles have such a limited life. I wonder if there are any other options beside graphite...

Badpeter, I would redo the mold.  When plaster casting I always had "fins" at the parting lines especially with multi-part molds - seldom had leakage (ill fitting mold) though. Looks like you have some kind of hybrid sand/plaster type of mold.  How much water do you add to the mix (very little = sand, lots = plaster), also sand requires no baking to expel the water.  I used to get a ready-made metal casting plaster in 20 lb bags from a local aluminum plaster metal casting operation - worked fine for smallish copper alloys but since plaster of paris burns at 2200 F I could never reuse the molds.  Not very familiar with sand casting mechanics though most use it today - materials are cheaper than plaster, sand is naturally porous so venting is less of an issue, and resulting castings have better physical properties than plaster castings because the metal cools faster in a sand mold. Like plaster molds, sand molds can never be reused either, AFAIK.

Found this cool Foundry Manual produced by the Navy that has a lot of good practical info - it's huge but has lots of hyper links:
https://maritime.org/doc/foundry/index.htm

Crucible question is good one, unfortunately I don't know if the quality of graphite induction crucibles varies or not, but I do know graphite is very soft and I suppose very magnetic, hence the high temps we are getting.  I know gas fired salamander crucibles are more durable and less "chalky" therefore maybe less susceptible to induction erosion currents.  Wonder if they conduct as much heat or not, and if they available in cylinder form. 

How many melts have you had with that crucible?
What melt size  2,3 or 4 pounds did you have? 

Approximate color and what color changes if any did you notice that occured from copper melting to right before you pouring?
These colors are a guide only:
Light orange 1800
Yellow 1920
Light Yellow 2010
White 2190*


*2190 give or take a few degrees is where I would cast smallish silicon bronze castings and most all other bronzes - white color.  Not sure what temps to cast this hybrid Al/Cu that does not contain iron as I could find no exact info on this alloy.  Normally Al/Cu with 3% iron, small castings pour at 2400 close to cast iron temps. What difference not having 3% iron makes I can only guess that 2200 or white hot would be best pouring temps for your 88/12 alloy.

To increase convection stirring action you might want make the coil thicker,shorter, wider-spaced???  Peter said that on his 1.2 pound melt the metal was boiling.  It was not actually boiling (4644 F is boiling point of Cu) -- he may have had too much convection stirring which I believe is also not good (too much turbulence caused oxidation/dross).  Petespaco, you don't by chance remember achieving white hot temps with the bigger melts do you?

You are on the right track I think and trust one way or another you will do it.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 25, 2019, 07:58:29 PM
Quote
Peter said that on his 1.2 pound melt the metal was boiling.  It was not actually boiling (4644 F is boiling point of Cu) -- he may have had too much convection stirring which I believe is also not good (too much turbulence caused oxidation/dross).  Petespaco, you don't by chance remember achieving white hot temps with the bigger melts do you?

Okay, let's call it "bubbling", for lack of a more acceptable term.
I didn't notice any difference in radiated color between large and small melts.  They all "bubbled" a short while after melting. 
As far as videos go, the white balance setting and circuitry of still cameras and camcorders varies so much that what you see on a "screen" is NOT predictor of what the eye is seeing.  And, of course, different eye/brain combinations "see" color differently, too.
  I hate to have to dig into lens filtering, but might just give some a try  some day, to be able to show what the melt actually looks like.
You guys might want to look at the melting points for various alloys  of aluminum.
I just looked up a binary eutectic table for aluminum, just for starters.  the eutectic of aluminum and  copper is only 1018°F, for instance.

Also, badpeter,--- I noticed a current shunt in your latest video, but I don't see any wires connected to it.  Did I miss something?  Are you reporting mains current or are you reporting current into the heater driver board?  And, are you reporting gross or net current?
 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 25, 2019, 08:14:23 PM
I just tried melting some more copper with the 2500 watt unit.
It went well despite my making a newby mistake by putting to much cold metal into the molten copper in the crucible.
The video is here:
/>
Interestingly, the current dropped more than in previous melts as the copper first melted.  I think I have some ideas about that, which will require further testing, one of these days,  But, even at 24 gross amps, (18 amps net) and 48 volts or (864 watts),  the full  crucible sure did melt well.

Peter, Just watched your video again.  At one point you said the copper was boiling.  I think that may have been induction stirring of the metal because copper boils at 4644 degrees.  This stirring action produces what is called a meniscus where the top of the melt raises in center and lowers at crucible edges.  Sounds like there may have been  some pretty vigorous stirring, to the point of bubbling?  Stirring is good for alloying to a point, but too much, I would think, causes excessive oxidation/dross.  So maybe a lower frequency would be better for melting (longer or thicker or wider-spaced coil)?  BTW, how is your crucible holding out?

Noticed again that when you dumped in the extra copper the noise level dropped by what sounded like a factor of two.  I thought maybe you blew out one of the fans, but that would have been impossible since you have them hooked up separately.   I think you said the extra load caused that.  So some parts from the heater caused the noise, like transformers make noises for some reason, so noise is emitted from the coil, and load is like a single turn transformer that varies with load/sound somehow?  Just curious again.

Also wondering if you noticed a significant color change from your melt temp of 2000 (light yellow) to pour temp?  2190 is white hot and is where I used to pour small bronze alloy castings.



Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 25, 2019, 08:48:41 PM

You guys might want to look at the melting points for various alloys  of aluminum.
I just looked up a binary eutectic table for aluminum, just for starters.  the eutectic of aluminum and  copper is only 1018°F, for instance.

Also, badpeter,--- I noticed a current shunt in your latest video, but I don't see any wires connected to it.  Did I miss something?  Are you reporting mains current or are you reporting current into the heater driver board?  And, are you reporting gross or net current?

Ok, that is a low eutectic so I take from that nice tidbit of info, that maybe proper mixing took place shortly after everything melted and melting point was far lower than I thought.  So evidently, there is a huge gap between melt temp 1100 and possible target pouring temp of 2200.  Should have been a rainbow of color changes from melt to pour?

Good question on the amps - no clue here but hope to know.

Update: Badpeter, not sure on alloying, but I think you are supposed to melt the metal with the higher melting point first then add lower melting point metal???  Also, I think you should make some ingots of Al/Cu first, whatever size(s) best fits in your crucible.  For smaller melts, you could pour a load into water producing Al/Cu shot.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on May 25, 2019, 10:40:21 PM
Molds: I use 50/50 plaster / sand mix, also 2 plasters for 1 water. Found information suggests that pure plaster cannot stand heat shock very well so sand makes it softer (although weaker) so it doesnt crack. Oven treatment is super neccessary so the mould doesn't explode on contact with hot metal from steam forming throughout. (it dries for couple days too before that but it is not enough)
Pure sand casting doesnt have this issue, but it is a chore to work with. I ve used it in the past for my other propane vids.
Transformer would hum only slighlty louder on overload. The massive fan under it drowns any possible sounds. It is not a part of the system in any way and connects separately to mains power.
The shunt does nothing at the moment. Crappy ebay meter burnt out and i left the shunt until I get a new one. As I explained in the description, to measure DC current just divide power (blue meter) by DC voltage (orange multimeter) (aka 700w/46v=15a dc.) So I have about 15 amps dc going in the induction unit. It can also be calculated the long way by utilizing turn ratios on transformer and ac current on mains, but thats the long way.
The hot metal is yellow to white, and is quite bright. It even shine through thick insulation. It loses brighness quickly when crucible is extracted.

So basically now I am going to wait until i get another different crucible from ebay (also ammeter). If i see increased power with new crucible, it will be conclusive that graphite is responsible for the most power draw. 
Meanwhile I may cut the existing crucible in half and plug a small coil, see how that goes. 
 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 25, 2019, 11:46:32 PM
Molds: I use 50/50 plaster / sand mix, also 2 plasters for 1 water. Found information suggests that pure plaster cannot stand heat shock very well so sand makes it softer (although weaker) so it doesnt crack. Oven treatment is super neccessary so the mould doesn't explode on contact with hot metal from steam forming throughout. (it dries for couple days too before that but it is not enough)
Pure sand casting doesnt have this issue, but it is a chore to work with. I ve used it in the past for my other propane vids.
Transformer would hum only slighlty louder on overload. The massive fan under it drowns any possible sounds. It is not a part of the system in any way and connects separately to mains power.
The shunt does nothing at the moment. Crappy ebay meter burnt out and i left the shunt until I get a new one. As I explained in the description, to measure DC current just divide power (blue meter) by DC voltage (orange multimeter) (aka 700w/46v=15a dc.) So I have about 15 amps dc going in the induction unit. It can also be calculated the long way by utilizing turn ratios on transformer and ac current on mains, but thats the long way.
The hot metal is yellow to white, and is quite bright. It even shine through thick insulation. It loses brightness quickly when crucible is extracted.

So basically now I am going to wait until i get another different crucible from ebay (also ammeter). If i see increased power with new crucible, it will be conclusive that graphite is responsible for the most power draw. 
Meanwhile I may cut the existing crucible in half and plug a small coil, see how that goes.

Using plaster, OK.  If you cut 2 keys in each half before pouring the other half you should not have alignment problems. For a two-part mold it seamed like I always did 3 halves, the first half was disposed of and only used to scrape a good parting line to limit parting flash lines.  Not sure what ration of plaster to sand I was using and not sure of other additives they used, but the molds were very strong after air dried and still pretty strong when bone dry though much lighter.  You can skip the air drying and just oven dry vented between 300 and 450 timing it such that molds are 450 all the way through when ready to pour.  Yes, they must be bone dry - witness the king of random video - he pours into a wet plaster mold and it sounds like popcorn popping. :o
 
Yellow to white so maybe between 2000 and 2100 - Nice.  Not sure on your alloy but that may or may not have been the correct pouring temp. Eye protection is necessary somewhere thereabouts?

I just paid $50 for a 3000w PS though I have no clue if it will work.  It will be four 750w server PS's wired in series.
/>Would like to hook up so that input power is switchable between 12,24,36 &48 volts giving at least some sort of way to adjust power for whatever that is worth. Basically I want more power for melting, not ways to adjust to lower power.  Adjustable may have some unforeseen use, but not still sure if I can get it running stably with all four in series.  I have seen similar HP power supplies with 1200w @ 12v so if you put 4 in series you'd get 4800 watts, maybe useful somewhere down the road.  Or maybe 2 of these 3000w supplies everyone is using could also be combined in some way giving 6000 watts - now were talking!!  Supposedly, they work in series fairly easily, though Mads says in the video that large smoothing caps may be required to balance things out?  I guess I'll find out one way or another.  Also, no clue clue if hooking em up in parallel if possible?

That is a big crucible so maybe that's a good idea.  May have some life yet for testing at least, but be very careful with worn crucibles, they are fragile enough and even more so when 2000 degrees plus. Not sure what happens when a pot of molten metal exposes a coil but know it will burn right through most everything else.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 26, 2019, 12:26:49 AM
hightemp1"
Quote
Noticed again that when you dumped in the extra copper the noise level dropped by what sounded like a factor of two.
The change in noise came from the power supply.  When the current increases to some specific point, the fan's speed is increasesd and vise-versa when current goes down.  And that's what you heard.   My  comment at that time wasn't all that accurate, was it?

Nailing down colors to exact temperatures:
  I am not sure that all metals glow with the same colors at the same temperatures. Some googling does not help to clear this up.
But,  even the amount of backlight can have a huge effect on any particular metal.
That's why a blacksmith shop is often dimly lit.  When I am demonstrating the heat treating of fire strikers to the public, outdoors, it's tough to see the curie point, unless I sorta hide the part under the forge.  Even then, I miss it occasionally.
But just to give you an extreme example. when forging titanium, It gets unbelievably white-white-white in a short period of time.  I have never seen any other metal do that even when forge welding or watching them pour 15 or 20 tons of steel.  And, again, people have widely varying color perception abilities.
  I suppose I better get back out there with a thermocouple.  I am also going  to fool around with home made camera filters, but don't hold your breath.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 26, 2019, 12:55:15 AM
hightemp1"
Quote
Noticed again that when you dumped in the extra copper the noise level dropped by what sounded like a factor of two.
The change in noise came from the power supply.  When the current increases to some specific point, the fan's speed is increasesd and vise-versa when current goes down.  And that's what you heard.   My  comment at that time wasn't all that accurate, was it?


Noise Level:  Your comment was plenty accurate, I'm just, you could say "electrically challenged".

TC & Filters: screw the TC and Filters -- I'd just like to know what you see, with proper eye protection, when you melt a pound of copper for half an hour, but I expect, and rightly so, to not be holding my breath.    As I said before, I am in no hurry at all and I am just amazed how gracious you are with sharing your time and knowledge.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 26, 2019, 01:56:42 AM
So...
Casting: there were 3 problems with moulds: lack of air holes, difficulty aligning two sides, significant crack between two sides. I will redesign the way the mould is, hopefully 3d print something for the mould to address those issues. Also I hope it can be reusable. Riser can be increased too.
I still have one more test to run with lost PLA method, will see how that turns out.

Metal: It melted completely, but I didn't stir it enough and didn't skim. I think convection doesnt do much.  Will try borax as a lot of people seem to use it. It is weird that if you have 7% Al you get that golden shiny color. Try 15%... and it starts looking like it is all Al, althought most of it is copper! In other words, I have put too much Al in this alloy. resulting alloy is still quite strong though.

Here are some links from that foundry manual on curing casting defects:
https://maritime.org/doc/foundry/part3.htm#pg149
https://maritime.org/doc/foundry/pg157.htm
https://maritime.org/doc/foundry/pg159.htm
https://maritime.org/doc/foundry/pg161.htm
https://maritime.org/doc/foundry/pg163.htm
https://maritime.org/doc/foundry/pg165.htm
https://maritime.org/doc/foundry/pg167.htm
https://maritime.org/doc/foundry/pg169.htm
https://maritime.org/doc/foundry/pg171.htm

The color effect is such that some metals dominate color much more easily, I don't understand that either.

By weight, I think you want 88 percent Cu and 12 percent Al

 A primitive hardness test is just nailing it with a screwdriver and comparing marks with soft copper ingot or other metals you have lying around. Stength is putting it in a vice, if it does not brake after a few good wacks, your good to go.  Bending without weakening may be ok depending on use - just means it is malleable.


Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: T3sl4co1l on May 26, 2019, 04:38:40 AM
FYI, gypsum (the active ingredient in plaster) dehydrates in two stages: first to hemihydrite around 170°C, and then to anhydrite around 700°C.

Actually, looking it up, it seems it goes straight to anhydrite around 170°C, at least that's what the text claims (https://wfs.swst.org/index.php/wfs/article/download/231/231).  But the amount lost is just less than the total.  But more than hemihydrite.  It's like it's... quintahydrite, as it were (i.e., 1/5th of an H2O). The final total is plausibly correct (the exact figure is 20.93% water in stoichiometric gypsum).  So now I really wonder if this paper is missing something, or if it has to do with material purity (it was only "90% pure"), or if no one really knew the truth about gypsum dehydration and just kind of went along with it all these years because, who cares it's just gypsum, right?

Anyways-- I've never had problems when heating it to dull red hot.  But I've always seen exactly the bubbling you describe: not violent, but still too much for the material porosity and venting to handle without leaving bubbles.

FWIW, I usually use 1:1 to 2:1 sand (fine or sifted sand preferred) and plaster, for simple casting investment.

Protip: when the metal has fully solidified, drop the mold in a bucket of water.  The plaster will spall off, freeing the casting in no time. :)

Plaster-based investment is also reusable, just dehydrate in the oven to get back to the active hemihydrite form (hardens when water is added).  Needs to be smashed up finely, of course.

Tim
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 26, 2019, 05:16:48 AM
FYI, gypsum (the active ingredient in plaster) dehydrates in two stages: first to hemihydrite around 170°C, and then to anhydrite around 700°C.

Actually, looking it up, it seems it goes straight to anhydrite around 170°C, at least that's what the text claims (https://wfs.swst.org/index.php/wfs/article/download/231/231).  But the amount lost is just less than the total.  But more than hemihydrite.  It's like it's... quintahydrite, as it were (i.e., 1/5th of an H2O). The final total is plausibly correct (the exact figure is 20.93% water in stoichiometric gypsum).  So now I really wonder if this paper is missing something, or if it has to do with material purity (it was only "90% pure"), or if no one really knew the truth about gypsum dehydration and just kind of went along with it all these years because, who cares it's just gypsum, right?

Anyways-- I've never had problems when heating it to dull red hot.  But I've always seen exactly the bubbling you describe: not violent, but still too much for the material porosity and venting to handle without leaving bubbles.

FWIW, I usually use 1:1 to 2:1 sand (fine or sifted sand preferred) and plaster, for simple casting investment.

Protip: when the metal has fully solidified, drop the mold in a bucket of water.  The plaster will spall off, freeing the casting in no time. :)

Plaster-based investment is also reusable, just dehydrate in the oven to get back to the active hemihydrite form (hardens when water is added).  Needs to be smashed up finely, of course.

Tim

Good protip -that should help with castings physical properties too.  Did not know about reusing either. 

I think lost wax castings require heating plaster molds to 1200 for complete removal of wax residue/mold contamination, and to accept smallish castings/prevent freezing.

The bubbling issue appears that Babpeter has resolved it since he has little mixing, while Petespaco has excessive bubbling.  Difference between two setups include less power, bigger coil/crucible.  My concern will be reducing/limiting convection with a max PS that is Petespaco's size 2500W and using a large crucible that is similar to badpeter's large 1 kilo capacity.  No clue if that is doable or not?

Or maybe Badpeter has not resolved it and you are saying this is what has caused all the porosity in the casting knife blade area?  Have you ever melted anything, skimmed melt and/or used flux, poured, then examined for porosity?  Have you ever heard of anyone using these heaters to cast copper alloys successfully, other than ingots full of pockmarks?

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 26, 2019, 01:11:08 PM

Anyways-- I've never had problems when heating it to dull red hot.  But I've always seen exactly the bubbling you describe: not violent, but still too much for the material porosity and venting to handle without leaving bubbles.

Tim

Or maybe Badpeter has not resolved it and you are saying this is what has caused all the porosity in the casting knife blade area?  Have you ever melted anything, skimmed melt and/or used flux, poured, then examined for porosity?  Have you ever heard of anyone using these heaters to cast copper alloys successfully, other than ingots full of pockmarks?


Page 22 on link confirms your observations. Even states that mains power is not even suitable for melting copper alloys.  Author concludes that medium frequency furnace is the solution.  :(

https://core.ac.uk/download/pdf/146466277.pdf

I think this puts the kibosh on my zvs project. Unless someone has somehow overcome this bubbling issue?   I am assuming there is no way to increase frequency of zvs heater by a magnitude factor of 10 ???  I saw somewhere that both the dental and jewelry use induction furnaces successfully.  Don't know at what frequency and if special inert atmosphere is being used or not?

Author also concludes that Arc Furnaces are not appropriate for Al and Cu melting, also due to violent melting, mixing, dross, air bubbles, etc.
That leaves resistance melting.  Not nearly as exciting but it is a path or way out.  Non-metallic heating elements were recommended for copper, metallic fine for aluminum.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 26, 2019, 05:11:34 PM
So...
Casting: there were 3 problems with moulds: lack of air holes, difficulty aligning two sides, significant crack between two sides. I will redesign the way the mould is, hopefully 3d print something for the mould to address those issues. Also I hope it can be reusable. Riser can be increased too.
I still have one more test to run with lost PLA method, will see how that turns out.

Metal: It melted completely, but I didn't stir it enough and didn't skim. I think convection doesnt do much.  Will try borax as a lot of people seem to use it. It is weird that if you have 7% Al you get that golden shiny color. Try 15%... and it starts looking like it is all Al, althought most of it is copper! In other words, I have put too much Al in this alloy. resulting alloy is still quite strong though.

Power: something is going on with this! With the same setup, every run has less and less output. I tried a quick melt yesterday, max power decreased by another 100 w. I dont know whats going on except my theory with crucible getting thinner and thinner. Imagine if I could get all 1800 w out of this! I'd be able to melt iron (and add it to my alloy). Will have to wait until new crucible from ebay, if power goes high again, I d say that be the proof. Rather inconvenient that crucibles have such a limited life. I wonder if there are any other options beside graphite...

Badpeter, from previous post you may have noticed that I stumbled onto something that may be causing your problem.  Thank you T3sl4co1l !!!   Industry does not use low frequency induction for melting of Cu or Al because of the "bubbling" that causes gross oxidation. Industry standard for melting Cu alloys is Medium frequency furnaces  using frequencies 10x and greater than what you are using to minimize oxidation buildup. I think we are out on a limb here, but if you would like to pursue I have some suggestions.  Keep in mind that this advice is coming from someone who is clueless about induction and only did some hobby casting years ago:

1. Get frequency as high as you can.  Someone said actually removing caps.  Peter and others here hopefully can advise you here on getting maximum frequency. I think you have the 1800w version (less caps) so less bubbling is occurring - a good thing.
2. Also, Peter suggested using a glass covered flux but was not sure if melting point was low enough.  Maybe plain old borax?  Again, my experience with fluxes is limited, so experiment, or ask around.
3. Al/Cu alloy may be more prone to dross pickup, not sure.  Some tin bronze or Phosper/Coopper variation(10% approx) may be less susceptible to oxidation.  Purchase some from your local foundry, also ask for some phosper-copper shot(deox).  I have found that they are usually pretty good about that, fair prices, and even their gates, sprues, risers and such are usually very clean. Also, use only one alloy per crucible.  If dead set on using Al/Cu maybe decreasing the Al a little.  There are some strong Cu/Zn alloys but I have no experience with them.  My favorite silicon bronze probably would not be hard enough for knives.  Don't be afraid to ask a foundryman what he would use.  If your objective is more art than function then do not use Al/Cu.  I had good luck with above Ph/Cu alloy in the past.
4. Add glass cover flux with metal? Skim metal before pour and add phosper-shot if using above tin bronze (approx. 1% phosphorous - not sure what percent Cu is in shot so you will have to calculate).  Pour in a mold designed for the least amount of turbulence as possible with a riser and vents and a larger sprue.
5. I was thinking about bottom pouring (remember handle of knife was pretty clean) but can not think of a safe way to pull that off without metal going everywhere.  Peter has experience with cast iron so possibly has a safe suggestion.
6. Power - the faster you can melt the better.
7. Hopefully, others smarter than me will chime in.

Again, not sure if this is worth pursuing or not.  OTOH if you want to be a renegade, maybe you can get a good cast, come up with something novel, have bragging rights about being the first on youtube to do it, etc.  Personally I'd like to see you do it but that is irrelevant.

Regarding other forms of electric melting.  Arc is not used for copper - same reason even more violent oxidation stuff happening.  Resistance using ceramic elements is used for copper and is a proven safe technology, but I'm sure is not perfect either but probably more doable, I think.  DIY designs are freely available.

Update: I recall hearing bear bottles (brown glass) have a lower melting point around 1800 though that may be too high also?





Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 26, 2019, 05:53:20 PM
hightemp1:
Thanks for digging up that link.  Very interesting.
We have a few  companies our area that use induction furnaces for aluminum and copper alloy melting every day.  In fact, we use one on a regular basis and another occasionally.

On to the subject at hand:
Quote
Page 22 on link confirms your observations.  Even states that mains power is not even suitable for melting copper alloys.  Author concludes that medium frequency furnace is the solution.  :
https://core.ac.uk/download/pdf/146466277.pdf

I think this puts the kibosh on my zvs project.
------------------------------------------------------------------------------
Note what  the author of the link actually calls  "medium frequency":
"2.2.3 Choice of furnace freguency
In terms of metal melting, core less induction furnaces may be classified
into
(a) Low frequency - up to 200 Hz and including mains frequency (50 Hz) and
triple frequency (150 Hz).
(b) Medium frequency - 200 Hz to 10 kHz. Most popular frequencies in
this range are kHz, 2 kHz and 3 kHz.
(c) High frequency - over 10 kHz. Some small laboratory furnaces use
crucibles at these frequencies but this is generally experimental
work."
 -------------------------------------------------------
Take a careful look at some of my earlier videos.
You will see that we are running at about 38 Kilohertz with the 2500 watt ZVS induction heater, which is already 'way higher than the scope of that paper!
By the way, I think the 1800 watt ZVS induction heater ran at about 62.5 kHz.
---------------------------------------------------
Quote
Page 22 on link confirms your observations.  Even states that mains power is not even suitable for melting copper alloys.  Author concludes that medium frequency furnace is the solution.
Here, there's a slight misinterpretation-
He is saying that mains FREQUENCY (50 or 60 Hz) ---  not "mains power" is not suitable----,
And again, "medium frequency", to him, and in 1989, is 200 Hz to 10 kHz.

To sum up, we are already running at much higher frequencies than discussed in at least the first 30 or pages of that paper.


Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 26, 2019, 06:27:40 PM
OK, Game on Again !!!

regarding oxidation,  all that bubbling still can not be good so good foundry practice is advised.

Suggestion:
 Badpeter may be seeing less stirring action on 1800W heater than Peter is seeing on the 2500W because there are less caps therefore more frequency on 1800 unit?  But 2500w unit may melt faster.   Wonder if there is a way to get best of both worlds by having a variable step frequency on the 2500w unit.  Start out by using full 2500 watts until melted, then have a switch on the caps that somehow cuts out four of the caps so the frequency goes higher and you get less stirring?   Would power go down to 1800w, or is this feasible?


Have I redeemed myself or not? 
quote/paraphrase from the movie Dumb & Dumber

Update: Just dawned on me that continually adding metal to initial small molten bath may sorta give a permanent semi-molten state thereby cutting down on bubbling as well - as usual not sure?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: T3sl4co1l on May 26, 2019, 10:03:33 PM
I wouldn't be concerned about frequency, or stirring.  At least not until you're looking at aerospace alloys.

0. Use a thick, fairly conductive crucible (e.g., steel) to shield the melt from magnetic field.  (Marginal for aluminum, and not practical for cuprous alloys.)  Note that graphite has to be quite thick to provide much shielding.
1. If stirring causes oxidation, prevent oxidation (duh :) ).
1a. For cuprous alloys, use a cover of slag.  This should be mostly silica, lime and soda; you're really just going for a melted glass of modest viscosity.  Straight-up borax is too thin and will pour out with the metal.  (Add sand, alumina, clay, whatever to thicken it.  Add fluxes (borax, soda, lime..) to thin it.)
1b. Use a charcoal cover, or other reducing agent.  Using a graphite crucible to begin with, already helps a lot (graphite burns at red-hot temperatures, slowly but surely -- the thin blue flame is carbon monoxide burning off).
1c. Without any need for air in, or exhaust out, there is the option of using inert gas, or even vacuum. :D This is probably harder to pull off (e.g., you have to diffuse the inert gas into the porous refractory first, otherwise it's not doing much), or difficult in general, and expensive (vacuum hardware, plus feed-thrus to handle everything under vacuum?), but absolutely a possibility, something to think about in the long run maybe.
2. If stirring causes hydrogenation, just do a degassing step.  This is normal practice with aluminum.  May be harder with cuprous alloys.  Maybe the hydrogen can be burned out, say by dropping some CuO into the melt (push the slag aside so it doesn't dissolve into that)?  Maybe that doesn't work with zinc present, dunno.  Inert gas sparging will work for both, in any case.
3. Stirring probably causes a lot of slag entrainment (in aluminum, aluminum bronze, etc.), which is a good reason to use a flux (for aluminum, NaCl+KCl eutectic is fine, or you can get commercial mixes that include some fluorides as well).  This may introduce more hydrogen, so again, consider degassing.

Regarding removing caps -- for the same power, you need probably proportionally higher voltage, or matching equivalent to this.  Keep this in mind as the ZVS oscillator output voltage corresponds to supply voltage, and is limited by component ratings.

Tim
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 29, 2019, 09:40:16 PM
Just in case everyone isn't "burned out" on this topic yet,  I just uploaded my work coil characteristics spreadsheet today.

It details my own observations about several work coils that I have gotten with various ZVS induction heaters or that I have made myself.
It, like most of my stuff, is a work in progress:
http://spaco.org/Blacksmithing/ZVSInductionHeater/Work%20Coil%20Data.xlsx

By the way, just yesterday, I noticed that the inside diameter of the graphite  crucible that I have been using for all my copper melts so far has eroded by about half, from its original thickness.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 29, 2019, 09:50:22 PM
The link below gives a formula to calculate stirring.  My calculations show that the 1800W heater has far less stirring than the 2500 w heater by a factor of 10x, and the 2500w unit is insanely high.  I calculated that the 2500w unit has crazy off the chart high levels of 1250 while the 1800w unit is still very high at

I takes awhile to figure it out, but wondering if someone could independently verify my numbers when convenient for you?

https://www.foundrymag.com/meltpour/metal-stirring-coreless-furnaces/gallery?slide=6

Update: my assumptions were:
1800 unit had .75kw when melting started, @ 70000 hertz
2500 unit had 1.5kw when melting started, 35000 hertz

Even though they used different sized crucibles, I assumed they were the same, for comparison sake:  3.5" tall, 1.5" wide. 
Specific gravity of copper 8.5  ----  Resistance 1.75 best guess.


If these numbers are in the ball park then it will make quality castings with the 1800 unit very challenging. More significant though is without some type of modification to the 2500w unit, quality castings may be improbable.  Is it possible to lower stirring on 2500w heater buy a factor of 15x, or even 10x?  A major design change/mods of 2500w unit, to adapt for melting metal, may be in order and I am the least qualified person in the room to answer -  suggestions please ? ????

UPDATE: ABOVE CALCULATIONS WERE NOT CORRECT.  CASTINGS S/B DOABLE ACCORDING TO UPDATED STIRRING INDEX NUMBERS - RECALCULATED FURTHER DOWN.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 29, 2019, 10:07:53 PM

By the way, just yesterday, I noticed that the inside diameter of the graphite  crucible that I have been using for all my copper melts so far has eroded by about half, from its original thickness.

Nice work on the coils for 1K units -thanks. 

Tim turned us on to the fact that we start burning the shite out em at red hot colors.  I thought they did not start burning until much higher white temps were reached.  Again, don't know if the quality of china graphite crucible varies or not.  Tim advised thicker graphite, I think, but all the ebay stuff is only 5mm and I have not sourced any others - not sure they exist at reasonable price.   Adding some clay content would make stronger but would we still get the heat needed since clay makes crucible "cold"?).  I read average life on industry induction crucible is 30 heats, though industry crucibles may have varying amount of clay added for strength, and industry may also use other silicon carbide clay type that are more expensive.
Peter---how many "equivalent melts" can a forger get on a 99.95% graphite crucible?
Badpeter --how many melts did you get, did you crop off yours and do any more tests?

Maybe excessive stirring is also contributing to short life - do you notice any wave-like lines inside of crucible?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: T3sl4co1l on May 30, 2019, 12:13:24 AM
You may find this of interest:
http://hamwaves.com/antennas/inductance.html

Of course it doesn't give loaded Q, but unloaded L and Q at least are nice.

From Q and applied voltage, you can calculate coil losses, and then idle current, and get an idea of what loaded current consumption will be.

Loaded Q is best guesstimated from ratio of enclosed areas, and typical values for materials.

Tim
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 30, 2019, 03:39:39 AM
Guess there is a reason why I flunked physics.  I redid calculations, and got much better numbers:

FOR COPPER ON 2500 UNIT = STIRRING INDEX OF 125 = VIOLENT STIRRING
FOR COPPER ON 1800 UNIT = STIRRING INDEX OF 62 = HEAVY STIRRING

FOR BRASS ON 2500 UNIT  = STIRRING INDEX OF 62 = HEAVY STIRRING
FOR BRASS ON 1800 UNIT  = STIRING INDEX OF 31 =  LIGHT STIRRING

MAYBE THIS EXPLAINS WHY COPPER INGOTS TURN OUT SO BAD & WHY BADPETER SAW LITTLE STIRRING ACTION.

BETTER YET, THESE RELATIVE NUMBERS HELP PROVE THAT GOOD BRASS CASTINGS ARE DOABLE ON BOTH OF THESE HEATERS.  LOWER FREQUENCIES ON THE 2500w UNIT INCREASE STIRRING SO METAL CASTING WILL BE MORE CHALLENGING -- COIL DESIGN, GLASS COVERING, AND FOUNDRY PRACTICES SHOULD HELP (GLASS COVERING/FLUX WILL FURTHER LIMIT CRUCIBLE LONGEVITY ON FRAGILE GRAPHITE).  EACH ALLOY WILL HAVE A DIFFERENT STIRRING INDEX - COPPER ALLOYS ARE LESS CONDUCTIVE THAN PURE COPPER, THEREFORE LESS STIRRING TAKES PLACE.  SPECIFIC GRAVITY OF METALS ALSO PLAY A ROLE IN STIRRING, AND HELP EXPLAIN WHY ALUMINUM IS MORE DIFFICULT.  LIGHTER ALUM ALLOYS STIR EASIER, ALSO OXIDES/DROSS HAVE SIMILAR SG, SO DROSS GETS SUSPENDED IN THE SWIRLING BATH.  IN HEAVIER ALLOYS LIKE COPPER, MORE OF THE OXIDES FLOAT TO SURFACE, TO BE SKIMMED LATER. 

This is a clusterfuch - due to erroneous calculations I deleted a prior post and modified others (strikethoughs).  Please don't rely on unconfirmed stirring numbers, but based on Badpeter's knife casting and many other copper ingot castings, the calculated Stirring Index numbers on both Cu & brass seam reasonable.

SI formula clearly shows a direct correlation between stirring and a metal's castability, and proves that the ease of casting parts is affected by several variables including the alloy's resistivity, SG, and the melting unit's frequency, power, & crucible size.


Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on May 30, 2019, 08:00:08 PM
Just in case everyone isn't "burned out" on this topic yet,  I just uploaded my work coil characteristics spreadsheet today.

Not burned out at all! I read all the replies and learn a lot. I just do not have much to contribute with and are now also waiting for my 2nd try to buy fibreglass insulation from China :(
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 30, 2019, 08:17:32 PM
Just in case everyone isn't "burned out" on this topic yet,  I just uploaded my work coil characteristics spreadsheet today.

Not burned out at all! I read all the replies and learn a lot. I just do not have much to contribute with and are now also waiting for my 2nd try to buy fibreglass insulation from China :(

Mads, I just ordered the 2500w version and some crucibles (long/narrow 1.5 kilo size, no outer shell, the other is same one Peter is using with ceramic shell (approx 1# capacity) - both graphite).  Both from China so, yeah, about another month, at which time I will have probably forgotten about this project.  :(
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 30, 2019, 08:38:31 PM
I keep asking about modifying the 2500w board to get the higher frequencies best for metal melting, but no one seems to want to tackle the issue.  The design appears pretty simple so maybe modding is not too difficult; or, maybe because design is so simple modifications are more difficult?  Peter's coil notes in last post show the 2500w unit has more caps and I think advised me to use fewer caps.  How to safely go about doing that is Greek to me (if i remove existing caps do I need to add stronger ones - if i remove caps will i have to upgrade other components, add extra components, etc).  I have repaired TV, Stereos, by replacing bad caps, and measured bad transistors, fried diodes, under-spec'd voltage regulators, etc.  so comfortable on simple soldering end; but, as you all know, clueless on electronic circuits.  Peter's notes also show using narrow crucible/coils may increase frequency. Thought about using 5/16" coil but notes show this may have little if any effect. 

Any and all advice on modding these heaters to get higher frequencies more conducive to metal melting would be greatly appreciated.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 30, 2019, 10:17:29 PM
The issue of changing frequency on the 2500 watt unit:
   Sure, it is easy to do.  Just remove some capacitors.  Just make coils that have lower inductance.  Do just one or do just the other, or do both.  You can see how all this relates if you watch my 1000 watt videos and visit my 1000 watt pages.
  A while back, I spent time determining how fast the Mosfet driver circuit can get the Mosfets into full conduction  SO THAT A USER CAN DEPEND ON ALMOST 100% DUTY CYCLE.
I have done that to my own satisfaction.  The oversimplified (but nonetheless useful) number for upper frequency is about 120kHz.  Higher than that and out go the Mosfets.
  But almost ALL of the work that I have been doing lately is the learn the minimum coil inductances that will produce the desired power transfers without exceeding my 120kHz upper limit.
  I think i am pretty close to having this one "in the bag" too, at least from the inductance standpoint.   I won't even connect up a work coil with an inductance less than 0.7 microhenry to the 1000 watt unit.  And, for now, I wouldn't go less than that on the 2500 watt unit either, since, as far as I can tell, they have identical Mosfet driver circuits.
  However, just to add to the still  UNknowns, I am NOT confident that we can 100% transfer gate drive concepts directly to the 2500 watt unit since we have 3 sets of  drivers in parallel. 
  Lastly, for today, I am not sold on the REAL value of going beyond 120kHz anyway. 
Sure, I have heard the more power gets transferred at high frequencies, but this offset by thinner skin depths.  Oh yeh? And by exactly how much?  And, is it worth the effort, when I see that a WIDE variety of small-end commercial units seem to be quite happy in the 30kHz to 80kHz range.
   Lately I have been spending a lot of time trying to improve my video capabilities so I can do two camera shoots better and be able to show the bubbling copper better.  I feel that you guys may be getting too focused on stirring, so I want you to see exactly what I see.  To that end, I am now into camera light filters and white balance issues.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 30, 2019, 10:33:16 PM
The issue of changing frequency on the 2500 watt unit:

---Sure, it is easy to do.  Just remove some capacitors.  Just make coils that have lower inductance.  Do just one or do just the other, or do both. 

---Lately I have been spending a lot of time trying to improve my video capabilities so I can do two camera shoots better and be able to show the bubbling copper better.  I feel that you guys may be getting too focused on stirring, so I want you to see exactly what I see.  To that end, I am now into camera light filters and white balance issues.

Great, I will delve into that in due time!

Yea, I know, I'm compulsive about stirring.  Reasoning, correct or incorrect, is the lower stirring index # that I can get, the cleaner my castings should be; and, usagae of less flux that further damages crucible.  Funny how industry praises the advantages of stirring and before even doing an actual melt, I am already abhorring it.

Please don't go to the extra trouble on my account.  BTW - I think your low resolution videos are just fine.  You spend less time processing, etc and more time shooting pool, etc.(things that really matter!) If you feel extra clarity is required maybe adding a picture with link in video description is all that is needed.  Coming from someone who has never done youtube so, as usual, take with a grain of salt.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 31, 2019, 02:15:46 AM
The issue of changing frequency on the 2500 watt unit:

 However, just to add to the still  UNknowns, I am NOT confident that we can 100% transfer gate drive concepts directly to the 2500 watt unit since we have 3 sets of  drivers in parallel. 

 Lastly, for today, I am not sold on the REAL value of going beyond 120kHz anyway. 
Sure, I have heard the more power gets transferred at high frequencies, but this offset by thinner skin depths.  Oh yeh? And by exactly how much?  And, is it worth the effort, when I see that a WIDE variety of small-end commercial units seem to be quite happy in the 30kHz to 80kHz range.


 

Just by switching to some of the less conductive bronzes my figures move from brasses high stirring index of 62 to a medium SI in the low 50s).  Then, assuming we raise board's frequency by only 15kH (35 to 50) we now decrease SI to 40 or the high end of low stirring - closer to my target! 

If modding board is deemed necessary, do you think it would be safer to remove caps one at a time,  or make coils with lower inductance (there are two on board and just swap em)? 

Again, this is all my seat of the pants math that I frankly don't trust -- also, suspect you tire of me ambling on about these SI numbers - helping knobs like me has got to be demeaning - please know that we all so value your experience & kind advice.

Update: Unfortunately, as you increase ZVS heater power, the metal stirring goes up too.  Last calculations were based on power output of 1500 watts.  Assuming power level of 2000 watts (much better!), then frequency would need to go up even more from 35kH to 70kH, or doubling the present frequency.  So 2000 watts of power @ 70kH gives a descent SI of 38.  Does anyone think a 70kH MOD can be safely done - if so how specifically (please :))))would you modify the board.

Note: The power ouput on Peter's 1.2 lb melt test started at 2000kW and after all was melted power output ended @ 1250kW
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on May 31, 2019, 05:21:58 PM
Quote
If modding board is deemed necessary, do you think it would be safer to remove caps one at a time,  or make coils with lower inductance (there are two on board and just swap em)? 
My first choice would be to "make coils with lower inductance".  HOWEVER!!!!---  The two toroidal  chokes on the board are NOT the work coils.  They are there to decouple noise from the power supply.  It's the work coil that I would make with lower inductance.  That's what my work  coil data spreadsheet is all about.  I only list those two chokes  "FYI".
  I would NOT reduce the number of capacitors on the board.  All that tank circuit energy has to go somewhere and, with fewer of the same size capacitor, I'd thing they would heat up even more than they do now.  If you look at the way others build this kind of driver, you will see that they often attempt to spread that energy out by using many, many tank capacitors.  Of course in many commercial units, the capacitors are water cooled.  That's a whole different ball game.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on May 31, 2019, 06:26:01 PM
Quote
If modding board is deemed necessary, do you think it would be safer to remove caps one at a time,  or make coils with lower inductance (there are two on board and just swap em)? 
My first choice would be to "make coils with lower inductance".  HOWEVER!!!!---  The two toroidal  chokes on the board are NOT the work coils.  They are there to decouple noise from the power supply.  It's the work coil that I would make with lower inductance.  That's what my work  coil data spreadsheet is all about.  I only list those two chokes  "FYI".

Thanks again.  I'm just an ignoramus.  I will make the smallest diameter coil that will still fit crucible.  Taking the caps off board & water cooling them is only a last resort option for me. I now see that a Medium SI is actually industry recommended level for most copper alloys & we are there or close on many alloys without any mods on current setup, just like yours.  Metal exceptions being pure copper and similar good conductors like silver, sterling, gold, & pure aluminum.  You were correct again...I was making a mountain out of a molehill.   
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on June 03, 2019, 06:09:33 PM
Hopefully I will be able to contribute with some new insights once new crucibles and other stuff arrives!
I feel left out =)
Maybe I'll try something different meanwhile
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on June 06, 2019, 07:03:04 PM
Alrighty... while the next video is being cut I'll share these, hopefully new insights.

I received my new 2 kg crucible. I chaged the coil to a 5 turn coil. This time, I WEIGHTED the crucible before use so I can see how much graphite is lost. And, it seems, a lot! After an hour runtime a 234 g crucible lost 25 grams of graphite. And I can confirm with absolute certainty that power draw depends on amount of graphite - it was at a healthy 1083 W with newly inserted crucible, and by the end was about 970 w as graphite was lost. I will not be surprized if for my next melt I will start with those 970w. The amount of material in the crucible seems to have insignificant (although measurable) effect on power draw.
So this creates a practical problem. I do not want to pay 15-20$ for a new crucible every ten melts. Also, even bigger problem is that with a tiny crucible it is very inconvenient to remelt things you have casted - you d have to laboriously cut it up in small pieces.
A truly useful crucible should be at least the size of cookie tray ingots, and good for many melts.

So, my next R and D will be devoted to being able to manufacture crucibles with clay/plaster/sand/whatever mixed with graphite. There got to be a recipe somewhere. Or switch to steel container, but I have no idea where to get something with thick walls.
Another idea is two concentric pieces of pipe acting as a heat jacket. Loose graphite can be put between the cylinders and replenished as it burns out - to keep power output consistenly high.
But at that point, I might as well design a regular electric kiln that will not have those ridiculous problems with small impractical crucibles, constant power draw issues due to burning graphite and all other sorts of maintenance that come with the iduction setup.

Anyhoo, the new vid is coming!
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on June 06, 2019, 10:18:08 PM
badpeter:
  I just watched your earlier dagger casting video again.
If I hadn't said it earlier, I really appreciate your willingness to share.
From it I can understand your concern about being able to use your induction heater for melting that much material. 
If you have no particular attachment to "art" of induction heating, then going with an electric kiln, as you suggest in your recent post,  sounds like an appropriate solution.

However----  (isn't there always a "however"?):
I noticed that quite a bit of heat was coming out through the insulation in that video.  Whereas, the hard ceramic insulating cups that I am using NEVER show ANY signs of glowing at all on the outside.  I wonder if conditions would change significantly if you were to obtain such a crucible of the size you want.

Also--- about the depletion of the graphite:  the carbon can't really oxidize if there's no oxygen, right?   I 'm sure we have all read about commercial melters using inert gases, but that would be hard to do for us, I think.
But, what if we used a tight fitting cover?  The existing oxygen would be used up pretty quickly and then oxidation would be minimized.  We would only open the crucible to add material.   I have seen crucibles that have such a cover.
  For my own system, I will make some covers.  A guy gave me a 2" X 4" X 24"bar of graphite several years ago, so I have plenty of material  to experiment with.

For one source of graphite, the farm machinery companies around here used to sell quart size containers of powdered graphite for lubricating corn planters.  It wasn't too expensive.  Might be one approach to your inner and outer steel shell idea.  Just pour in more graphite powder as (and if) it still depletes.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Bert911 on June 08, 2019, 11:24:28 AM
Hi,

Do you think, there is an principal limitation to the ZVS Royer circuit, like efficency or maximum Power output, compared to more complex used circuits?
Except for the savety and that it's difficult to adjust your output power.

I mean with cooled mosfets in parallel you can achieve really high currents and there are some pretty nice ones out there, which can handle 600V with fast switching like the ixth62n65x2.

Furthere more I tested the 2000W 45A 20-70V induction Heater with the LCD panel.
It uses 4 (2 parallel) IRFP260 so you really shouldn't go over 70V, tried it and got an big arc. The Heatsink was glued on and removing it would proabely also destroyed them. Now im trying the ixth62n65x2.
After trimming the Shunt with tinn the current reading was within 5% acuracy beofre it showed an 3 times lower value. It has also an poti for limiting the current below 45A, if the treshhold is reached it switches off, so it's more a protection for the power supply.
It normaly tests the ouput and the Mofets before switching on, that's a nice feature.
Unfortunaly the unit doesn't show the frequency.
I could achieve a Power consumption of 3000W. If you want, you can make a Solderbridge over one of the two Shunt to bypass/reduce the current limitation. You maybe want some watercooler for the Mosfets the, to keep the original Mosfets and therefore the Resistance down.
I worked with frequencies from 40 kHz up to 200 kHz. Not sure how well the gate signals were or if theres a way to reduced the switchable Frequency. That was a task for the future.
I already orderd a new one and the new fancy Mosfets so hopefully I can compare them.

Another tipp, the used copper pipe shouldn't be to thick. If it's to thick you maybe reduce the resistive losses, but with the thicker tube you can't achieve strong magnetic field due to the larger volume of the coil.
I'm going to use 6mm with 4.1mm inner diameter. The next lower pipe commonly aviable would be 5mm with 4.1mm that's much less area. Bigger pipes aren't not woth the extra used space in my opinion. Most cheap 15kW heaters also uses 6mm pipe.

With kind regards Robert
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: T3sl4co1l on June 09, 2019, 04:44:08 PM
Do you think, there is an principal limitation to the ZVS Royer circuit, like efficency or maximum Power output, compared to more complex used circuits?
Except for the savety and that it's difficult to adjust your output power.

And stability, because it's just a dumb oscillator and doesn't always start up at all, or at the intended frequency (more a problem for high frequency oscillators).

So yes, that's all.  Like how a car is an engine on wheels, with steering.  It's not like you need a throttle, or brakes, or a windshield. ;)

So, that's why we design more complicated circuits.  They're not very complicated really.  Tesla coil drivers have been made worse than what's needed for this.  (My typical controller circuit is implemented in about 200 components, maybe not something you really want to build a kit of, but not at all impossible.)

Tim
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on June 09, 2019, 06:50:35 PM
T3s---:
I don't have any recent experience with "the more complicated circuits", but, regarding the "ZVS Royer circuit", please tell me more about:
Quote
---doesn't always start up at all, or at the intended frequency (more a problem for high frequency oscillators).

I ask because I don't think I have had either of these problems.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 10, 2019, 12:44:07 AM
 ::)
Alrighty... while the next video is being cut I'll share these, hopefully new insights.

I received my new 2 kg crucible. I chaged the coil to a 5 turn coil. This time, I WEIGHTED the crucible before use so I can see how much graphite is lost. And, it seems, a lot! After an hour runtime a 234 g crucible lost 25 grams of graphite. And I can confirm with absolute certainty that power draw depends on amount of graphite - it was at a healthy 1083 W with newly inserted crucible, and by the end was about 970 w as graphite was lost. I will not be surprized if for my next melt I will start with those 970w. The amount of material in the crucible seems to have insignificant (although measurable) effect on power draw.
So this creates a practical problem. I do not want to pay 15-20$ for a new crucible every ten melts. Also, even bigger problem is that with a tiny crucible it is very inconvenient to remelt things you have casted - you d have to laboriously cut it up in small pieces.
A truly useful crucible should be at least the size of cookie tray ingots, and good for many melts.

So, my next R and D will be devoted to being able to manufacture crucibles with clay/plaster/sand/whatever mixed with graphite. There got to be a recipe somewhere. Or switch to steel container, but I have no idea where to get something with thick walls.
Another idea is two concentric pieces of pipe acting as a heat jacket. Loose graphite can be put between the cylinders and replenished as it burns out - to keep power output consistenly high.
But at that point, I might as well design a regular electric kiln that will not have those ridiculous problems with small impractical crucibles, constant power draw issues due to burning graphite and all other sorts of maintenance that come with the iduction setup.

Anyhoo, the new vid is coming!


Bads, come on -- cut that sucker - how did everything turn out !!!

On the narrow crucible problem.  Agree, cutting up castings, etc. to fit these narrow crucibles is a pain.  Suggestions include making and pouring your own alloys into self-made pre-heated ingot molds that are long & narrow.  Also, I have seen wide-body graphite crucibles, but I think stirring increases with width so a less conductive alloy may be advised?  I cut up pieces using a band-saw, or saws-all.

Making own crucibles and eliminating oxygen are both good ideas but may be difficult.  Clay bonded crucibles may not get the heat we want?  Possibly ramming  graphite within a concentric 1 piece u-shaped steal tube, then sealing top with high temp ceramic that hopefully seals off oxygen?  With copper alloys, you then have to apply some sort of hot face lining to the inner metal to prevent metal contamination - similar lining would be necessary for an all stainless steal crucible?  Obstacles include longevity of lining, metal, and O2 elimination, plus cost competition with graphite.

Dross/slag further limits crucible life so using alloys that don't require as much additives may extend crucible lives.

  Losing 10% or more each melt means that after 6 melts crucible is reduced by half and since the crucible is what is heating/melting our metal, you are correct this is a big problem. Assuming $21/crucible & 7 melts/ crucible life -that is $3 crucible cost per melt - approximations only - not good ?  Three dollar crucible cost would be approx 10x the energy cost (assuming 1000 watt for 1 hour ?).  I see that the alternative furnaces that use electric resistant elements may also be using 100% graphite so crucible life may not be much longer?  However, by nature I would think that clay-type crucible would be usable with resistance furnaces so crucible life may be 2-3 Xs longer  - but maybe heat time/Watts consumed go up ??  Fatter graphite, like 10mm thick or more would be nice but where to source economically?  Lastly, with the power limitations we have on our ZVS units, we are pushing the limits on max. quantity of metal that can be realistically melted.  Personally, I hope to be able to melt 1 to 3 pounds of copper alloys into useful castings weighing two ounces to two pounds.  That is more than 10 times what an acetylene torch can melt, and quieter/cleaner than a propane setup.  Alternative as we both know is resistance melting.  I did not think of or compare the two methods beforehand so hopefully induction will work out.

As you can see,  I mostly only have more questions to your questions.    :-\ 
To some extent, we are pioneers here, discovering, solving, understanding problems as we go.  Many here at not at all interested in the melting side of things and only want to create large sparks.  ::)
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on June 10, 2019, 03:18:01 AM
This isn't really a "reply" to previous posts, but just a tiny bit of additional information  about the molten copper----

I just uploaded this youtube video about the looks of the surface of the molten copper:
/>
It's not my best work, but just another step toward better photography.
I also measure the temperature of the molten copper a couple of times.
I'm in the process of making several improvements that I hope will benefit those of you who haven't yet actually peered into a ZVS induction heater's graphite crucible with molten copper in it.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 10, 2019, 04:19:17 AM
Do you think, there is an principal limitation to the ZVS Royer circuit, like efficency or maximum Power output, compared to more complex used circuits?
Except for the savety and that it's difficult to adjust your output power.

And stability, because it's just a dumb oscillator and doesn't always start up at all, or at the intended frequency (more a problem for high frequency oscillators).

So yes, that's all.  Like how a car is an engine on wheels, with steering.  It's not like you need a throttle, or brakes, or a windshield. ;)

So, that's why we design more complicated circuits.  They're not very complicated really.  Tesla coil drivers have been made worse than what's needed for this.  (My typical controller circuit is implemented in about 200 components, maybe not something you really want to build a kit of, but not at all impossible.)

Tim

Just curious Tim, for you, how hard would it be to mod this board so amps could be approximately maintained throughout melting process? 

In Peter's bigger melting videos amps start out at about 38 and finish somewhere around 25.  That is a 33% loss or about 600 watts of power. ???
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: T3sl4co1l on June 10, 2019, 05:24:58 AM
T3s---:
I don't have any recent experience with "the more complicated circuits", but, regarding the "ZVS Royer circuit", please tell me more about:
Quote
---doesn't always start up at all, or at the intended frequency (more a problem for high frequency oscillators).

I ask because I don't think I have had either of these problems.

Startup is an issue at very low Q factors.  Transistor gain is quite high so it's not usually an issue at common Q factors.

You might just see it with copper coils tightly fitted around steel pipe, or with lossy coils (say a stainless pipe coil used for process heating).

Frequency is a problem for this circuit for example,

(https://www.seventransistorlabs.com/Images/Fluo1.jpg)

which runs around 500kHz, but can lock into other modes in the 400-650kHz range depending on what load you have attached.  The problem is if there is extra capacitance at the load, in addition to what's on the oscillator board itself.  The connecting wires between oscillator and load form another resonant circuit, and the frequency response becomes much more complicated.  In this case, the transformer is a step-up and its secondary has a resonance near this frequency, even if I didn't put explicit capacitors on it.

As I said, you're less likely to have problems with this, at low frequencies where the capacitors are more likely to act together.

Tim
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 10, 2019, 04:09:10 PM
This isn't really a "reply" to previous posts, but just a tiny bit of additional information  about the molten copper----

It's not my best work, but just another step toward better photography.
I also measure the temperature of the molten copper a couple of times.

Peter, what interested me the most in your last video me is after the melt & pour when the emptied crucible was reinserted inside coil, the amps shot way back up to 38.  This tells me that maybe very little graphite was lost in the approx 15 minute melt.  More curiously, is that the reduced amps from melt start to melt pour (38a to 25a, or 33%) simply seems to have more to do with the metal going from solid to liquid state - maybe how this self-oscillation circuit mysteriously works - can someone please explain to me why amps crash so much from cold metal to melted metal, or am I just missing something obvious again?? 

Oddly, on Bad's last reported melt the amps only went down approx 10% in an hour.  Not sure if amps would have recovered if he had reinserted the empty crucible into coil after melt.  So Bad's 1800w board appears to behave differently than Peters's 2500W board, but there is also different starting power input levels (1kw vs. 1.8kw), and different run times (15 min vs. 60 min) so comparison is fuzzier. However, possibly a huge difference in individual board behavior. Bad's smaller amp loss may be due more to crucible burning and Peter's larger amp loss may be due to board design, self-oscillation??

Also, the blue gas burning was clearly evident towards end of the video so I am thinking crucible burning is accelerated as crucible temp increases.  Blue flame may have just been some crude on copper too.

update: Lastly, the pryometer went up to about 2015f and then you said that it stopped climbing rapidly.  I suppose it could have gotten to 2200 but just would have taken progressively longer?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: T3sl4co1l on June 10, 2019, 08:23:43 PM
When the load resistance is low (e.g. cold copper), it tends to reflect rather than absorb magnetic field; this reduces power consumption compared to a better matched load.

Whether current draw increases or decreases with heel size and temperature, depends on which side of best match you're running at.  Which in this case I think depends on the crucible thickness, and porosity (overall conductivity), as far as how much magnetic field it absorbs before reaching the copper within.

Tim
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 10, 2019, 10:12:13 PM
When the load resistance is low (e.g. cold copper), it tends to reflect rather than absorb magnetic field; this reduces power consumption compared to a better matched load.

Whether current draw increases or decreases with heel size and temperature, depends on which side of best match you're running at.  Which in this case I think depends on the crucible thickness, and porosity (overall conductivity), as far as how much magnetic field it absorbs before reaching the copper within.

Tim

Cool, so if I got it right - the higher the metal temp the higher the metal resistance, then the higher the resistance the lower the power output of unit.  Thought there might be a relationship.  This could be my downfall since I would like to melt higher resistance alloys like silicon bronze that have very high resistances = not enough heat to melt.  Unfortunately, most of the good copper casting alloys have very high resistances.  Also, bad for me is the less resistance the greater the stirring.  The intricacies of induction melting are challenging.  Will try to squeeze all the power I can out of a 2500w unit but it may prove to be under powered for my size melts.  Please correct me if my resistance/zvs power relationship is wrong - thank you!
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on June 11, 2019, 03:42:39 AM
There is very little increase in current, if ANY as the copper heats up (but before it melts).  The decrease in current that I report occurs at exactly the moment when the copper melts.  That has been my direct observation EVERY time I have melted copper.  And, the deeper the pool of molten copper, the more the current decreases.
  I don't see the "cold copper" phenomenon mentioned recently.
Also, since the addition of solid copper to the crucible does not seem to increase the current, I don't think the copper itself is participating to any significant extent in speeding up the melt.    It's radiation, convection and conduction that is transferring the heat from the glowing crucible walls, to the copper, in my opinion.
  ---So I will go "out on a limb" and say that I don't think the copper alloys that you want to use will present any worse of a melting problem than does the copper that I am using. 

Now for my hypothesis as to why the current drops just when the copper melts:  I think the molten copper actually "shorts out" the graphite as the copper makes intimate contact with the whole wall of the crucible.   

Lastly, for today, about stirring:
As you know, I am trying to be able to show exactly what is going on in the bottom of the crucible.
  I almost got to performing  my improved camera color-shift filtering test today, but--
A friend and I had a chance to inspect a pig iron smelter from the 1880's and we did do it.
Well worth the 20 mile trip.

  I hope we will all see that there isn't much "violence" going on in the crucible, after all.
I did get some graphite covers and additional insulations pieces cut and did a dry run to test for a 2 camera shoot, though.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 11, 2019, 08:29:11 PM

  ---So I will go "out on a limb" and say that I don't think the copper alloys that you want to use will present any worse of a melting problem than does the copper that I am using. 

Now for my hypothesis as to why the current drops just when the copper melts:  I think the molten copper actually "shorts out" the graphite as the copper makes intimate contact with the whole wall of the crucible.   

Lastly, for today, about stirring:

Absolutely, videos clearly show amps dropping once molten metal bath starts and peek when the pot is full (38a to 24amps, I think) - somehow the molten metal bath inhibits power getting to the graphite.  Now we kinda know why amps crash so much, but unless we can rig up some kind of controller circuit to force more power to crucible I guess just knowing exact cause doesn't do much good anywho.  Tim, stated that they are not really complex for him.  Adding two hundred components is way beyond my pay grade.  But possibly something less complex, that just gives a little more power would be sweet??

According to my SI calculations copper, silver, gold (the super-conductive elements) all have very high stirring indexes.  This has been confirmed by one of the retailers of these units, for what that is worth.

I would have liked to have seen the old-time pig iron smelt - make America great again! :(

update: Just got my crucible, like yours.  A little dissappointed how thin the graphite is (11mm top rim, and a little over 6mm body).  Also was hoping the graphite would sit flush with the ceramic shell, but instead graphite is 2mm higher so minimizing O2 to outer graphite would be more difficult.
Also, received the 1.5kg the other day.  No shell and the body is 8mm thick.  Thought about coating it with that high temp spray kit, but that stuff is so expensive and I've heard that because graphite is so slippery that it may not hold for very long.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on June 11, 2019, 08:57:37 PM
Sorta OT, but---
Quote
I would have like to have seen the old-time pig iron smelt - make America great again! :(

This smelter hasn't actually been in operation since about the year 1900.  We just checked it out for historical curiosity sake.
See:
https://www.youtube.com/edit?o=U&video_id=0zTf4WdYXc0

If you want to see us MAKE "Wrought Iron" from iron ore, go here:
https://www.youtube.com/edit?o=U&video_id=493AsqZ4P54

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 11, 2019, 09:15:00 PM
Sorta OT, but---
Quote
I would have like to have seen the old-time pig iron smelt - make America great again! :(

This smelter hasn't actually been in operation since about the year 1900.  We just checked it out for historical curiosity sake.
See:
https://www.youtube.com/edit?o=U&video_id=0zTf4WdYXc0

If you want to see us MAKE "Wrought Iron" from iron ore, go here:
https://www.youtube.com/edit?o=U&video_id=493AsqZ4P54

links did not work, for me?  Any ideas for a "simple" -more power" controller board add-on for these heaters?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on June 12, 2019, 02:13:23 AM
Quote
links did not work, for me?  Any ideas for a "simple" -more power" controller board add-on for these heaters?

Hmmm--- I just tried both links and they did work for me.  Just a simple "click" on each one and there I was.

I don't have any idea for a "more power" controller board to add on.  However, maybe you want to bit the bullet and buy the $1000 unit that is 7 KW.
https://www.ebay.com/i/221663967797?chn=ps
(This is just one of the many sellers)
  That ought to do it.  You will, however, need a TIG  water cooler for it and they run at least $400 more.

I still feel that it's a "heat in vs heat out" equation.  You only get 3412 btu's of heat for each 1 KW of electricity.  So, if you are losing more than you are putting in, the temperature quits rising, right?   There is still the opportunity for any or all of us to conserve more heat.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on June 12, 2019, 02:17:20 AM
Alright people, here it is...
Thank you for the valuable suggestions - I did not think of oxygen issue at all. I wonder how less the deterioration will be if I add either a ceramic shield or somehow make the whole thing happen in CO2 atmosphere (yes, for my kind of "lab" that be a bit of an overkill!)
I will probably entertain the idea of getting a drilled out STEEL crucible somewhere. Will need to be very creative with that. (Curie point a possible issue?).
Will do maybe one more melt/vid with graphite crucible, not to get too repetitive.
Anyways, the current vid is self-explanatory. lots of commentary and measurements given.
If I cleared PLA, it would have worked wonderfully.
Wonder if i should melt the sphinx (since its not great) or leave it as souvenier and recast my dagger with new material (i found a small source of copper recently!)

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 12, 2019, 05:36:48 AM
Alright people, here it is...
Thank you for the valuable suggestions - I did not think of oxygen issue at all. I wonder how less the deterioration will be if I add either a ceramic shield or somehow make the whole thing happen in CO2 atmosphere (yes, for my kind of "lab" that be a bit of an overkill!)
I will probably entertain the idea of getting a drilled out STEEL crucible somewhere. Will need to be very creative with that. (Curie point a possible issue?).
Will do maybe one more melt/vid with graphite crucible, not to get too repetitive.
Anyways, the current vid is self-explanatory. lots of commentary and measurements given.
If I cleared PLA, it would have worked wonderfully.
Wonder if i should melt the sphinx (since its not great) or leave it as souvenier and recast my dagger with new material (i found a small source of copper recently!)

/>

You know what they say Bads, third time is a charm - I vote for the dagger :)  Just remember, they are never perfect and will almost always need finishing of some sort.  If you like polished look a skilled finisher can do miracles but does take time and experience.  Personally I prefer the as cast look with minimum finishing, but you really need clean castings, good mold design, etc. for best results. 
Don't know anything about PLA but maybe it is similar to wax and needs a 1200f burnout cycle? 
Steel crucible may work, considering you'd like a 1-5 percent iron in your dagger; though, I really have no clue how much iron would be absorbed, and if too much is absorbed it may freeze.  Also, could get contamination of other elements depending on composition of steel?  I would think it would be physically safe, but Peter would know much better than me how strong various steel crucibles may be at 2200-2300 degrees and maybe recommend some type of steel. 
I really don't know how to tackle the burning crucible issue.  I previously mentioned some ideas but they are experimental only.  Go to go for now - thanks much for posting!

Update: Just thought of one potential problem with molding the dagger -- maybe the large thickness transition  between the handle and the blade.  I don't know the best way to design it.  Possibly, have the handle act as sprue, probably have more of a taper transition between the handle and the blade, and/or place a core in the handle so overall thickness will be more uniform?  This will of course be just one the many possible molding, casting, finishing, etc. problems you many encounter.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Bert911 on June 12, 2019, 02:55:12 PM
Just a quick response from my side.

The higher the resistance of the material, the better it is for heating it. Steel for example, it starts with 60% power than rises to 100% due to increasing electrical resistance and goes down to let's say 40%. These are just estimations, based on my analogue 80a current meter.

So getting up with the temperature is for non magnetic materials in theory better. That would at least explain the overall low power consumption for these relatively high voltage.

For a steel crucible, I can say the following. The normal steel will get destroyed from the air/oxygen and the aluminium, starting at 700°C/1292°F. For example a 2mm thick steel crucible will be destroyed after around 10h to 20h completely unusable at 900°C. Steel with 25% Cr, 20% Ni will withstand the oxygen in this temperature but will still be "eaten" by the aluminium. There are some coatings which slow the process like "3M Bornitride Suspension WP"

http://technical-ceramics.3mdeutschland.de/en/products/3m-release-agents-and-lubricants.html#c880 (http://technical-ceramics.3mdeutschland.de/en/products/3m-release-agents-and-lubricants.html#c880)

Cost in Germany around 40€ for 1 litre.
They also have other coatings. But they only slow down the process. They are likely to crack and there is the crap happening again....

For controlling the real power of a ZVS Circuit, you can basically only lower the input voltage, for all the other stuff you have to change components on the board.

Best regards Robert
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on June 12, 2019, 04:05:28 PM
Badpeter-
  Maybe try casting the dagger vertically?  That way it would be certain to fill.  I think they do cannons that way.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 12, 2019, 05:02:38 PM
Quote
links did not work, for me?  Any ideas for a "simple" -more power" controller board add-on for these heaters?

Hmmm--- I just tried both links and they did work for me.  Just a simple "click" on each one and there I was.

I don't have any idea for a "more power" controller board to add on.  However, maybe you want to bit the bullet and buy the $1000 unit that is 7 KW.
https://www.ebay.com/i/221663967797?chn=ps
(This is just one of the many sellers)
  That ought to do it.  You will, however, need a TIG  water cooler for it and they run at least $400 more.

I still feel that it's a "heat in vs heat out" equation.  You only get 3412 btu's of heat for each 1 KW of electricity.  So, if you are losing more than you are putting in, the temperature quits rising, right?   There is still the opportunity for any or all of us to conserve more heat.

The error I get is "Oops, something went wrong" on a blank white page - maybe just my server?

On conserving more heat:  I will likely be using kaowool with the narrow 1.5 kilo crucible and may try thin layer of koawool with the smaller crucible/liner combo.  Problem with porous insulation is the contribution to faster burning of graphite.  Unless there are some trade secrets we are not privy to, short graphite crucible life  may be a necessary evil in trying to adapt these heaters to melters.  Also, of course, the extra space the insulation uses will further decrease BTUs to crucible because insulation pushes proximity of crucial farther away from coil so I may be slicing my kaowool to maybe 1/2" (use gloves and mask when handling wool).

On $1500 furnace -->  I can only dream :(. 

Bert,  excellent stuff!  My take is because metal is better conductor maybe heat will not be great enough to melt copper even with insulation?  If it could melt, then maybe a descent  alternative considering we are currently only getting 6-10 melts with graphite anyhow?  And, if copper alloys without aluminum were used maybe iron crucible life would significantly exceed a graphite one?   A simple temperature test I suppose would be to find metal tube (preferably stainless) surround it with insulation and see if white hot temps can be attained.
Other unknowns exist, including previously mentioned metal contamination effect (good or bad).



Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 12, 2019, 05:08:44 PM
Badpeter-
  Maybe try casting the dagger vertically?  That way it would be certain to fill.  I think they do cannons that way.

Vertical may cause too much turbulence.  I was thinking at an angle, not to steep, maybe 25 degrees with the blade edge pointing down.  Just a wild guess though.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Bert911 on June 12, 2019, 07:46:41 PM
One approach could be a cheap steel pipe, weld a cover on the end and maybe use some of this coating.
The material costs are so small, if you have the welding stuff.

Keep in mind that using normal tools on really high quality stainless can ruin them.

I tested different pipe diameters and most of them easily reached the 2 kW power limit of my heater. The heater has a current and voltage sensor, so I can't go that high above the rating.
I can trick the unit by changing the components, but it's also nice to have a real power display without adding 50% or so on top.
I have a beefy 5kw adjustable unregulated power supply for 0-200V that comes handy, so it was no problem to get the highest possible power output with different shapes.

For example, I start with 30V with 1.5 kW then it rises up to the 2 kW and then it reaches curie temperature it goes down to 800W, and I turn the Voltage up to 60V and have my 2kw again.

These exact numbers depend on many things like the material, the coil, the geometry of the workpiece. Just some figures out of my mind, to get the point.
At the end of next week I can do some more tests.

If you use steel, you should really look the temperatures of the mosfets. I was able to get 50 A even at 30 V with good fitting steel tubes.

I think my coil has an inner diameter of 40 mm/ 1 5/8" something like that and 6 turns, runs with 157 kHz and uses an overall capacitance of 0,86 µF, which are rated for 100 A.

Robert
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 12, 2019, 08:45:31 PM
One approach could be a cheap steel pipe, weld a cover on the end and maybe use some of this coating.
The material costs are so small, if you have the welding stuff.

Keep in mind that using normal tools on really high quality stainless can ruin them.

I tested different pipe diameters and most of them easily reached the 2 kW power limit of my heater. The heater has a current and voltage sensor, so I can't go that high above the rating.
I can trick the unit by changing the components, but it's also nice to have a real power display without adding 50% or so on top.
I have a beefy 5kw adjustable unregulated power supply for 0-200V that comes handy, so it was no problem to get the highest possible power output with different shapes.

For example, I start with 30V with 1.5 kW then it rises up to the 2 kW and then it reaches curie temperature it goes down to 800W, and I turn the Voltage up to 60V and have my 2kw again.

These exact numbers depend on many things like the material, the coil, the geometry of the workpiece. Just some figures out of my mind, to get the point.
At the end of next week I can do some more tests.

If you use steel, you should really look the temperatures of the mosfets. I was able to get 50 A even at 30 V with good fitting steel tubes.

I think my coil has an inner diameter of 40 mm/ 1 5/8" something like that and 6 turns, runs with 157 kHz and uses an overall capacitance of 0,63 µF, which are rated for 100 A.

Robert

Wow, fascinating stuff, all way over my head.  My take on your variable PS, is since we don't have a sweet ass PS like that I'm thinking we could sort of simulate one??  Using graphite as an example: Peter's crucible uses 38 amps when new, but if it had more graphite (wider/taller) maybe it could use 60 amps?  But since we are limited to 50 amps on the 2500w unit we would have to gradually lower the crucible (instant variable amp/power regulator),  lowering it completely when metal is all melted, or when fully inserted and safely stays below 50 amps??  Granted this is a crude variable PS - problems include accelerated burning of lower part of crucible, rigging up a lowering device.

On stainless steel,  yea I tried to file it once and it practically filed my file. ???

I am not a welder but always wanted to try.  Also, thought about welding a SS tube but did not think welding would hold at 2300f, but then again I know nothing about welding either, but ignorance has never  stopped me from blabbing out ideas.  Not sure if same "dipping crucible" concept holds with steel because of curie stuff happening :-\ ?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on June 12, 2019, 09:14:43 PM
hightemp1:
Quote
But since we are limited to 50 amps on the 2500w unit we would have to gradually lower the crucible (instant variable amp/power regulator),  lowering it completely when metal is all melted, or when fully inserted and safely stays below 50 amps??
I think this is an excellent idea.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: T3sl4co1l on June 13, 2019, 03:04:37 PM
Yes, exactly.  There is a best-load matching condition.

Too low resistivity, and there's no voltage drop in the work, the magnetic field reflects nearly perfectly, and frequency simply rises, instead of DC current being drawn.

Too high resistivity, and there's no current flow, the magnetic field penetrates nearly perfectly, and little DC current is drawn.

We know that, somewhere inbetween, current consumption is higher.  We don't necessarily know if we're on the rising or falling slope of that curve, or optimally on the peak, but we know definitely that there must be a peak, somewhere between these extremes!

This has been today's shop application of calculus (https://en.wikipedia.org/wiki/Rolle%27s_theorem).  Cheers. ;)

Likely, it just so happens that a full heel of molten copper is below the peak, while a chunk of steel above curie temperature, is above the peak.  Graphite of this thickness is certainly above.

Different people have different setups, landing above or below as well.

The positioning of that peak, is driven by the number of turns of the work coil, how close it is to the work, the characteristics of the power supply, etc.  Frequency affects skin depth, which affects the equivalent load that a given chunk of material reflects.

If you're below the peak, I would suppose, try adding another turn or two; if below, remove a turn or two.

This type of supply also delivers the most power into the lowest Q factor, and the lowest impedances.  Q can be lowered by reducing the distance from coil to work.  (You need some space for insulation, and loads like copper won't give a terribly low Q anyway, even at point blank distance; there's only so much room to push in this direction.)  Impedance can be lowered by reducing inductance and increasing capacitance.

Tim
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on June 13, 2019, 06:46:24 PM
Here's my final test of watching the surface of the molten copper with better camera filters:
/>
Pete Stanaitis
----------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: badpeter on June 13, 2019, 06:47:12 PM
^^^Yesterday I found a steel valve cap just the right size, that probably can be used as a crucible. Can't wait to test it out! needs a bit of cutting which ill have to go around somehow. I wonder whats the draw is going to be. Due to its shape it cannot be taken out of the coil though.
Wish I had any welding tools or such, maybe Ill find someone who has that.
Dagger hopefully on Friday=) New patented "sunken" mould style will prevent metal from escaping on the sides. 8)

I wonder if it is a good idea to find optimal power consumption by shorting turns of the coil to quickly change its characterictics (easier than fiddling with caps) and watch how output changes.

peterspaco - satisfying to watch the molten surface! I may try something like this, my dslr has some manual settings for video, maybe I can get away without filters even. or use an old floppy to cover the lens!
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 13, 2019, 10:22:12 PM
Here's my final test of watching the surface of the molten copper with better camera filters:
/>
Pete Stanaitis
----------------

-Melting action is indeed very clear now - nice!  Definitely more of a shimmering than bubbling. Maybe even more of a medium stirring rather than heavy stirring.
-I'm betting that is dross on the sides covering most, effecting some of the mixing while also highlighting it?  Wondering what the best way to skim it off would be? 
-2200 degrees Fahrenheit with very little preheat time is sweet! 
-Insulation was smoking starting off.  Extraction of fumes especially inside, sure would not hurt (again, I just use a hepa filter sized to my box fan cranked up on high).  Some sort of high temp spreadable ceramic on lid/insulation, hot face I think it's called, may reflect heat back into crucible better?
-Just weighed my new crucible similar to yours = 138.5 grams, 6.33cm.  Hoping for 10 melts?

Bads, nice score on the cap buddy!  Trying with some sort of brushed on high-temp ceramic, or as-is? 
-sunken mold sound interesting.  To cut a couple keys in plaster, I just used a small spoon to hog out a little plaster on first layer.
-no clue on shorting stuff - the word itself scares me.
-yeah,watching molten metal, kinda like sitting in front of bonfire - sweet!
-tomorrow I will post some before/after, cut-up pieces of a sprue and a gate that I purchased from a local foundry some 30 years ago. 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on June 14, 2019, 12:24:48 AM
I thought I'd wait until someone else mentions the "shorting turns" thing.
When I did that, (unintentionally, early on)  I always liked to have a bunch of extra Mosfets and gate components around.  And even some heavy copper wire to use for replacing evaporated pcb traces.  For me, half a second is tooooooo  looonnnggg!  But maybe your heater's circuit is different.
See:
https://spaco.org/Blacksmithing/ZVSInductionHeater/1000Watt12to48VoltZVSInductionHeaterTroubleshootingGuide.htm
for how and WHY I used to have to repair them!
I have seen people do that "shorting" thing with other units, but you'd better be sure that your driver  board itself has a current limiting function.  Just because your power supply may have current limiting is NOT good enough.  It's the degradation of gate signals that kills the board.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 14, 2019, 02:38:13 PM
Two identical sprues on top left.  Top right is a gate, I think.  No idea what end products were.  Notice the diameter 3/4" of sprues - they must have been large castings.  Pieces on bottom were cut to fit in our small crucible (the larger ones still might not be small enough - :()  First melt may be making ingots to fit my crucibles.  Alloy is silicon bronze and total weight is five pounds.  Took me 30 minutes to cut several pieces - much, much slower than cutting up wood, though my bandsaw is in dire need of a good tune-up.  Used a regular 6 tooth/in wood cutting blade at lowest speed (maybe 600 rpm?) and it worked just fine.  Still have not received my induction heater from China.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Bert911 on June 14, 2019, 10:19:02 PM
I finished the circuit for the unit.

Printing on the Board:

2000W Rated Power
input voltage DC24V- DC70V
maximum input current <48A
ZVS2000S High frequency induction heating
8300515

As far as I can tell, the controller checks for a mosfet fault before switching the relay on.
Voltage, current a temperature are always checked.
You can add an extra external switch for short heating applications.
There's a potentiometer to limit the max current.

The controller does NOT know if the circuit is oscillating or not, but you can check your setup with a low current setting. In case something went wrong, the unit should open the relay faster, that's handy before start working with different coils/voltages or after a repair for obvious reasons.

If the coil inductance is way too high/low, it can detect a mosfet fault.
The components with an "X" are unknown.

Due to the applied voltage of 100V, the mosfets, transistors, optocoupler and the resistor "R15" blew up. This resistor is crucial for the proper working. I have to wait for the new one board to get the value to repair it properly.
If I had removed the heat sink, the mosfets were most likely also got damaged and since there was no information available.
I wanted to know, how high I can get with the input voltage.

The measured current from the unit was way too high, I shortened the shunt and adjusted the value with some extra tin.
With that method you can also increase the maximum power output relative simple.

The optocoupler for the fan/pumpe is always on.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on June 15, 2019, 02:00:16 AM
Thanks so much for putting up the schematic.
  I'm not too sure yet, exactly how the system "checks the Mosfets" before turning power on, though.

Re: your comment about max input voltage:
The datasheet for the IRFP260N says 200 volts max.  Somebody on this forum has said the you can expect to see pi X the input voltage across the Mosfet.
If that is true:
48                     55                       65  Volts In
3.14159            3.14159             3.14159
150.79632   172.78745   204.20335 Volts across Mosfet



This seems to imply that you might get away with 55 volts, but 65 volts would be over the top.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Bert911 on June 15, 2019, 09:25:07 AM
I updated the schematic a bit (removed the 1k resistor after the relay) and there are two versions now.
One with the real component names and one for ltspice simulation with other components.

If the relay is open, the voltage over c3 and c4 goes up to 22V, after that the unit can activate the mosfets and recognize a voltage drop.
If the mosfets are shortened or the transistors are damaged the voltage won't rise/fall.

Since the 200V are the minimum rating, it should be OK to 70V.


Changelog:
-added diode name/diode model to the simulation
-added correct transistor model to the simulation
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on June 16, 2019, 12:03:50 AM
Quote
Since the 200V are the minimum rating, it should be OK to 70V.
I respectfully disagree.  On the datsheet that I saw, "200" was the ONLY number.  There was no entry at all in the "max" column.

Where do all the "uC" points go?
It appears to me that they would all originate at the output of the opamp, but I guess I just don't understand that kind of a schematic diagram.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Bert911 on June 16, 2019, 09:38:15 AM
The µC stands for microcontroller.
I didn't bother to track the all the way back to it.
Of course this isn't the whole schematic since there is also an lcd display.

https://www.banggood.com/2000W-ZVS-Induction-Heating-Module-Board-Flyback-Driver-Heater-Good-Heat-Dissipation-With-Coil-Pump-Power-Adapter-Kit-p-1464491.html?cur_warehouse=CN

5V worth arguing? Rule of thumb is 4 times.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on June 16, 2019, 03:39:30 PM
Thanks for clearing that up and thanks for the link.  Now I understand that there's a lot more going on than I thought.
That's quite a package!
When I multiply 65V X 45A, I get 2925 watts.  I wonder why they only rated it as a 2000 watt unit. 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 16, 2019, 07:06:48 PM
Thanks for clearing that up and thanks for the link.  Now I understand that there's a lot more going on than I thought.
That's quite a package!
When I multiply 65V X 45A, I get 2925 watts.  I wonder why they only rated it as a 2000 watt unit.

Robert, 2.2kw was stable?  maybe making this a superior design & deal?  Input, 120 or 240, make any difference on output?  2 to 2.5kw area makes a 20 amp circuit on 120 volt doable.

Update:  Per Product Description - (Short Circuit/Overload: Input current is greater than 40A, voltage greater than 55V, enter protection).   If so designed, then should not go over 2.2kW, I presume.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Bert911 on June 17, 2019, 08:01:10 AM
Thanks for clearing that up and thanks for the link.  Now I understand that there's a lot more going on than I thought.
That's quite a package!
When I multiply 65V X 45A, I get 2925 watts.  I wonder why they only rated it as a 2000 watt unit.

Robert, 2.2kw was stable?  maybe making this a superior design & deal?  Input, 120 or 240, make any difference on output?  2 to 2.5kw area makes a 20 amp circuit on 120 volt doable.

Update:  Per Product Description - (Short Circuit/Overload: Input current is greater than 40A, voltage greater than 55V, enter protection).   If so designed, then should not go over 2.2kW, I presume.


The heater goes in protection mode, if the voltage is below 20V, greater than 70V, current greater than 48A or the heat sink temperature over 65°C.
Even fast peaks are detected and trigger the protection.

The mains voltage doesn't matter at all, the input voltage of the unit is relevant. Btw my supply uses 3x380V.

Note that the idle loses increases with a higher input voltage, but also the heating capacity of the coil, it also increases the oscillating current through the coil. So the capacitors need to handle these extra current.
These caps are rated for 50A effective current, this is already reached at 54V input voltage and the standard coil.

ICap, peak=2*Pi*f*UCap,peak
UCap, peak≈Pi*Uinput             // measured Peak Voltages from multimeter could be off by 50% due to high frequency
ICap, effektive≈ICap, peak/1.414

This oscillation current through the caps shouldn't depend on the load.
With 3kw input wattage there could easily be a loss of 500W or more.

Pworkpiece=Pinput-Pcoil+cap-Pmosfet-Premaining circuit
Pworkpiece≈Pinput-Pidle-Pmosfet

The mosfet losses can be assumed to be relatively small, probably under 100W with that heat sink. These depend on the Input current/voltage and switching frequency.

The 48A is already a seriously big current that's why I bought some new mosfet with a higher voltage rating. A heating power of effective 2kw at the workpiece is most likely enough for most applications, but you can't always reach this with the standard configuration for specific shapes like bolt heads.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Bert911 on June 20, 2019, 02:14:55 PM
Hello everyone,

I got around to test the new arrived heating unit. It came with a different coil (4 instead of 6 windings).  I have to correct my thought about the current limiting potentiometer. It's a bit strange, you can limit the current and you can trim the shunt resistor.Therefore, a real current meter is a have to. Maybe it's some sort of current limiting in the first 50% and shunt tuning with max current at the last 50% or something.

Here are the results from some testing:
Coil with 6 windings, 50 mm high, 45mm inner diameter
with no workpiece:
In 24,4V 45W; Out 74V peak on the caps
In 38V 90W; Out 112V peak on the caps
In 50V 185W; Out 152V peak on the caps
In 60V 250W; Out 188V peak on the caps
The voltage over the caps are pretty much spot on the PI times input voltage. Due to the higher oscillating current, the power loss increases also.

Heating up a workpiece:
Steel bolt 22mm diameter and 60 mm high
In 52V, used power 1600W at beginning, 2100W peak and 700W at around 900°C.

I maybe solder a copper pipe direct at the capacitor connection to cool them with the water too. A cooled heat sink for the mosfets would be great to, since the get a little bit warm at high currents.

The used resistor is a 5.1 Ohm, so I updated the schematics, the simulation is much more stable now.
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 22, 2019, 06:10:01 AM
Picked up one of these crucibles. Price is not too bad. Not 100% graphite, but has some silicon carbide in it along with some clay, maybe.  Hoping it is more durable but kinda doubt it, though it is thicker than the graphite ones -almost 11mm.   Chipping may mean it has less bonding strength and is more prone to breakage.  Hoping it heats as well, seems to have a lot of graphite (feels slippery like ones we are using).  Holds a little over 1 pound of copper.  OD is 3" wide by 3" long so with insulation the coil would have to be wider, about 3.75" and about 6 turns.  ID is 2.2" but narrows to 1.5". 

https://www.ebay.com/itm/Silicon-Carbide-Graphite-Crucible-Tool-Metal-Melting-Casting-Cup-Shape-Furnace/254233218790?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Description says: "Surface can be treated with antioxidant."  Sound like Chinenglish, not sure what it means.  Maybe this silicon/graphite type will accept some type of wash that could increase longevity?

Having some power supply issues so it maybe sometime before I actually melt anything, if ever.  :(
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: T3sl4co1l on June 22, 2019, 05:21:58 PM
If that's the traditional combination of materials, it probably won't be very conductive, and the coating is a flux/slag material that tends to bead up on the surface and drip off (presumably can be refreshed with the right goop).

SiC is a modest conductor when heated, making microwave heating possible, and maybe induction still (but maybe with higher voltages/frequencies than are available here).

SiC-graphite crucibles can practically be quenched in water; they're very tough, as ceramics go. :)

Tim
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 22, 2019, 05:47:22 PM
If that's the traditional combination of materials, it probably won't be very conductive, and the coating is a flux/slag material that tends to bead up on the surface and drip off (presumably can be refreshed with the right goop).

SiC is a modest conductor when heated, making microwave heating possible, and maybe induction still (but maybe with higher voltages/frequencies than are available here).

SiC-graphite crucibles can practically be quenched in water; they're very tough, as ceramics go. :)

Tim

Maybe it will do induction with insulation?  If not, then this crucible may be relegated to melting lower temp metals and/or internal non-ferrous heat treating..

Microwave melting sounds interesting - wonder how long to super heat a pound of bronze in modified microwave with a typical 1200 watt microwave. 
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: flyrod on June 22, 2019, 08:36:34 PM
I finished the circuit for the unit.

Thank you for posting that!  I think that explains the 6 small transistors I was seeing in the ebay pictures.  I tried to ask about it in this thread:

https://highvoltageforum.net/index.php?topic=167.0

So the 12v for the gate drive comes from a separate DC-DC board?

Also, what is the big capacitor that is not part of the tank?  Is this C8 in your diagram?

Finally, are there no bypass capacitors on the supply to Q3 and Q4?  If not, I would be curious to see what this point looks like on a scope.

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Bert911 on June 24, 2019, 04:58:39 PM
I finished the circuit for the unit.

Thank you for posting that!  I think that explains the 6 small transistors I was seeing in the ebay pictures.  I tried to ask about it in this thread:

https://highvoltageforum.net/index.php?topic=167.0

So the 12v for the gate drive comes from a separate DC-DC board?

Also, what is the big capacitor that is not part of the tank?  Is this C8 in your diagram?

Finally, are there no bypass capacitors on the supply to Q3 and Q4?  If not, I would be curious to see what this point looks like on a scope.


Hi there,

The first transistor switches the supply voltage for the gate drivers on/off, the second one switches the relay and the other 4 are the gate drivers.

There's an additional 12V power supply for the microcontroller, fan, pump and the gate circuit.

The capacitor C8 reduces the current/voltage spikes during the mosfet switching, reduces the impact of wiring inductances from the power supply and smooths the measured voltage for the microcontroller.

The transistors have no additional parts, there is no gate resistor, unfortunately.

I tested my new arrived "IXFX100N65X2-ND" mosfets and they didn't really work. During the ordering I didn't notice the slower body diode.
The heater didn't turn on at voltages over 40V or with a load and stalled at 20A current using. So I hooked up my Tektronix 2225 with my "very fine" 100:1 Chinese probes and measured the gate signal with the analogue differential add function. With no loads it was a near perfect square wave, not like the simulated one, but with increasing current the ringing was really visible.
Like 20V peak-peak at 20A. Could be a bad measurement setup, the Chinese probes or most probably the slow diodes.

Similar to this, just worse:
https://highvoltageforum.net/index.php?topic=648.msg4550;topicseen#new

As supposed here, it gets worse with the rising current.
https://www.mikrocontroller.net/topic/207864#2057621

Also the Voltage in the oscillator tank dropped at 20A to 60% from the unloaded one.

So I'm waiting for the real 260n mosfets, measure them with the scope and maybe buy some other mosfets with higher voltage ratings.
Something like these:
https://www.digikey.de/product-detail/de/rohm-semiconductor/SCT3030ALGC11/SCT3030ALGC11-ND/6204894

But I want to check the circuit with the original mosfets first, maybe they are also ringing, but with them it doesn't matter as much.

Greetings
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 25, 2019, 05:45:55 AM
On the melting side of things, I found some good melting/foundry links:

https://ia600205.us.archive.org/23/items/Handbook_of_Lost_Wax_or_Investment_Casting_Sopcak/Handbook_of_Lost_Wax_or_Investment_Casting_Sopcak.pdf

On molding here is an oldie but goodie.

https://books.google.com/books?id=c98mAQAAIAAJ&pg=PA88&dq=induction+furnace&hl=en&sa=X&ved=0ahUKEwjHvIjwu43iAhVCPK0KHR5XCtkQ6AEITTAG#v=snippet&q=frequency&f=true

A Dental Casting Manual of Sorts:

https://ia800106.us.archive.org/35/items/DTIC_ADA173766/DTIC_ADA173766.pdf

Dude who tours knife-making- Note the flatness of the swords and blades - Uniformity in thickness:

/>

Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on June 29, 2019, 06:58:06 PM

0. Use a thick, fairly conductive crucible (e.g., steel) to shield the melt from magnetic field.  (Marginal for aluminum, and not practical for cuprous alloys.)  Note that graphite has to be quite thick to provide much shielding.


Tim

Too thick is bad as well.  This quy could not melt anything with a 20mm thick custom made crucible.  More power required to heat larger crucible so can't get to superheat pouring temps.

https://highvoltageforum.net/index.php?action=post;quote=4362;topic=530.120

UPDATE:  Correct link should have been:
/>At the end of video he realizes that 20 mm is too much of a load.


Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on June 29, 2019, 08:34:31 PM
Maybe we should split the topic, so that this stays for electronic discussion of the heater and the heating of metals, but the melting, casting and crucible discussion has its own thread?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on July 04, 2019, 06:19:51 AM
Pushing the limits with a small work coil for annealing brass cartridges.  For this video, I make and use the smallest diameter work coil yet for the 1000 watt ZVS induction heater.   Although I focus on annealing a brass cartridge casing very quickly, this video is really a next step in my ongoing series about work coil design and  work coil frequency limits for reliable circuit operation.
It is here:
/>
(I stopped just BEFORE melting anything)

Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: hightemp1 on July 07, 2019, 04:06:47 AM
Finally got my ZVS unit.  While hooking things up, I realized that my planned auto fuel pump is not designed for pumping water and would ruin the pump in short order.  Wondering what would make a good pump?  I scavenged a small radiator and a huge server fan that will be used for water cooling. Possible pumps I have thought of:  submerged aquarium pump, auto windshield pump - any other ideas, and I assume flow rates of above mentioned pumps would be sufficient?
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: johnf on July 07, 2019, 04:48:48 AM
garden supply store for fountain pump or similar
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on July 07, 2019, 05:24:20 AM
While the garden pump mentioned by johnf might work okay, I suggest this one (or one like it):
https://www.amazon.com/Yosoo-Circulation-Brushless-Selling-Quality/dp/B00PXXJEHE/ref=asc_df_B00PXXJEHE/?tag=hyprod-20&linkCode=df0&hvadid=198097979185&hvpos=1o5&hvnetw=g&hvrand=17395343945830728741&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9019020&hvtargid=pla-348418857326&psc=1
  It's about USD $20.00, but is rated for hot water, which certainly will be an issue.
As I mentioned in my most recent video, I was pleasantly surprised at how much flow I got from it even when using the 1/8 inch OD copper tubing for the coil.  I also suggest that you try to minimize the "head" that the pump has to work through.  In other words, don't put the radiator  all the way down on the floor making the pump have to work real hard.  As the "head" gets higher, the pumping rate and pressure goes down.

Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on July 07, 2019, 05:28:04 PM
Subtopic:  Adding a (Cheap?) frequency meter (counter) to my induction heaters-

I just uploaded this page:
https://spaco.org/Blacksmithing/ZVSInductionHeater/MakingAFrequencyCounterForNoisyAndSineWaveInputs.htm

It's actually a story about what NOT to do, but it turns out okay.


OT for hightemp1:  That water pump that I recommended----  I would not consider it to be submersible.

Pete Stanaitis
---------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Mads Barnkob on July 07, 2019, 08:19:33 PM
Pushing the limits with a small work coil for annealing brass cartridges.  For this video, I make and use the smallest diameter work coil yet for the 1000 watt ZVS induction heater.   Although I focus on annealing a brass cartridge casing very quickly, this video is really a next step in my ongoing series about work coil design and  work coil frequency limits for reliable circuit operation.

Pete, I love your videos, you really get deep into the topics, do a lot of experiments and share your results. Kudos to you Sir.

You video editing was also really good in this video, keep up the good work, it had a nice flow and I enjoyed it from start to end!
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: petespaco on July 08, 2019, 09:13:42 PM
Thank you for your kind words, Mads.

Now I want to talk about a "Cheap" Frequency counter for the ZVS Induction heaters:

I am certain that most people who get into this  "World of  Electrical Oscillations" do have frequency measuring equipment.

I have an old Tektronix 422 Oscilloscope that I use to roughly measure frequency by counting  the number of cycles I see on the screen at a certain sweep rate.  I also have an inexpensive tiny battery powered DSO-112 touch screen  oscilloscope that has the ability to give me a digital readout of the incoming frequency (if I push the right spot on the screen at the right time and have my magnifiers on).

  That's not much in the way of frequency measuring equipment, but it's enough for my BENCH needs at present.

  However, my projects are often scattered about my shop and I can't always get my bench scopes to the unit under test.  And, the touch screen of the little scope isn't all that handy for big fingers when I am in a hurry.
  I currently have two different ZVS induction heater systems.  My testing has made me realize that it is important, for several reasons, to know the tank frequency at any given time, so I decided to dedicate a frequency counter to each machine so I'd instantly and always know the tank frequency.
  To that end, I went through an all-too-lengthy process to choose/build/connect "cheap" frequency counters to my heaters.  (I even built two extra sets while I was at it).
  Here is a webpage that I just put up which takes you through the whole process:
https://spaco.org/Blacksmithing/ZVSInductionHeater/MakingAFrequencyCounterForNoisyAndSineWaveInputs.htm

Pete Stanaitis
--------------
Title: Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
Post by: Bert911 on July 09, 2019, 08:45:17 AM
Good thing that my multimeter can handle these frequencies, after making a new coil it's always interesting how the inductance is.

As I said earlier I had some ringing Problem with the IXTH62N65, because of there really slow body diode (typ. at 25°C 445ns).
As a comparison, the IRFP260N (typ. at 25°C 268ns) there's also some ringing but it's not consistent and gets better with heavy load.
I also tested some FGH80N60 (typ. at 25°C 61ns).

The FGH80N60 worked just fine but they got really hot.
So I ordered some IKW50N65 (typ. at 25°C 52ns) which should be fast and cool enough. I'm not sure how the relative slow turn off delay time will matter, but I'll see.

The next step for 200V input voltage would be some good capacitors, but there are the next problems.
With these high frequencies and "high" voltages of the standard 2000W heater model, the capacitors are already at there current rating with only 50V input.
So that's not a long term solution. Other similar capacitor like the used MKPH-R or Dawncap aren't that suitable. If the overall capacitance is too low the frequency rises, which is a bad thing for the slower IGBT. If the capacitance per capacitor is too high, the currents are way above the ratings.
So more small capacitors would be the way to go, but these won't fit more than four on the original board.
I could make a new board/circuit, but the start/stop routine works really good and I want to keep it (no need for turning off the big PSU...).

With 4 capacitors which cost 15 to 25 € I can also go with some seriously big stuff like this:
http://www.eectech.store/cs-30122-solid-state-high-frequency-film-capacitor-12uf-500vac-p0319.html
Which can handle the voltage, current and frequency. It's even smaller than 4 big film caps. With some cutting at the PCB it will fit nicely.

However, my previously statement with the 6mm copper pipe isn't true in that case and a10mm pipe is probably more suitable.
Since I have two units, I put 4 originals caps on the IRFP260N unit with 6mm; 1/4" connectors and the second one with the new cap, IKW50N65 and 10mm; 3/8" connectors.

That should power things up. The oscillating current should increase with the higher capacitance which lead to a smaller working coil, which should be better for screws and non crucible stuff, which I use it for.

There's also a mains powered updated version of this circuit:
http://www.joretronik.de/Oszillatoren/Oszillatoren.html
This can't hang up at start up and can't fail like the royer.
Since my PSU is limited somewhere to 4kw-6kw I don't see a need to go higher up in voltages/complexity right now.
I'm not that firm with high energy stuff at that high frequency. For a proper circuit you would need a start/stop routine, over current protection, a relay and so on.
I try to get this thing working, build a housing and that's it, since i have seen many "super big" induction heater projects which never finished...