Author Topic: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"  (Read 21495 times)

Offline petespaco

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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.

Offline DICKEYBIRD

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'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. :)
« Last Edit: March 30, 2019, 02:53:08 PM by DICKEYBIRD »
Milton from Tennessee ya'll

Offline petespaco

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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:


Online Mads Barnkob

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'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.

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

Offline Hydron

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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.

Offline DICKEYBIRD

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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.
Milton from Tennessee ya'll

Offline badpeter

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^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=)




 

Offline petespaco

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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
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Offline DICKEYBIRD

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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
Milton from Tennessee ya'll

Offline petespaco

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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
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Offline petespaco

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

Offline DICKEYBIRD

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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?
Milton from Tennessee ya'll

Offline petespaco

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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
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Offline petespaco

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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

Pete Stanaitis
---------------
« Last Edit: April 18, 2019, 10:10:26 PM by Mads Barnkob »

Offline DICKEYBIRD

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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! ;)
Milton from Tennessee ya'll

Online Mads Barnkob

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

Offline badpeter

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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.






Offline petespaco

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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
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It is Here:
 
/>

Offline DICKEYBIRD

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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! :-[
Milton from Tennessee ya'll

Offline petespaco

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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.

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