Author Topic: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"  (Read 4244 times)

Offline Mads Barnkob

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I built my first experimental cheap power supply and it was a great success!

12 laptop chargers put together for 40V 51A.

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Offline flyrod

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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?
 

Offline Mads Barnkob

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5 minute stress test at full power. 1800 Watt peak input power.

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Offline petespaco

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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
---------------

Offline Mads Barnkob

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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

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Offline Mads Barnkob

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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"
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Offline petespaco

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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".



Offline Mads Barnkob

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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 :)
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline badpeter

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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=).
 



 

Offline Hydron

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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.

Offline badpeter

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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...

Offline Mads Barnkob

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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.
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Offline kamelryttarn

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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

Offline petespaco

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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

Offline badpeter

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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.

Offline petespaco

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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.

Offline badpeter

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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!

Offline petespaco

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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.


Offline Hydron

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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!

Offline kamelryttarn

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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?

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