Sciencemadness Discussion Board

Combining low voltage induction heaters?

3DTOPO - 26-3-2016 at 15:14

Wow - induction heater technology has really dropped in price (I paid $400 for a 300 watt kit I never got around to assembling a few years ago). Here is a 1000w unit with work coil for $45:

http://www.ebay.com/itm/1000W-ZVS-Low-Voltage-Induction-Heat...

Is there anyway to combine these guys, perhaps with a plurality of work coils operating on the same inductor? Or could they be run in series or parallel? I just need more than 1000w and this would be amazing! Thanks!

Metacelsus - 27-3-2016 at 13:59

You'd need to figure out a way to make sure their phases match.

3DTOPO - 27-3-2016 at 15:03

Can you think of any way it should theoretically be possible? Any neat tricks perhaps by plugging them into power in the same phase perhaps?

Do you think it would work without matching the phases at all, like at some loss, or would it likely damage the drivers?

What if I used a separate graphite tube (in a water-cooled fused quartz tube with argon atmosphere) for each one in close proximity to each other (perhaps with a zirconia spacer), each with their own driver and work coil (on the outside of the quartz tube)? I know, not the same as my question, but I think this could be doable for a vacuum furnace. So it would be like this:
_ == _ == _
@ $ @ $ @
¯ == ¯ == ¯
Where:

@ = graphite tube
$ = zirconia spacer
_ = separate work coil/driver
= = air

In other words, if I make certain the graphite and the work coils don't touch, how close can the be?

[Edited on 27-3-2016 by 3DTOPO]

3DTOPO - 27-3-2016 at 17:48

I drew a crude diagram of the idea here:
multipleInductorIdea.png - 76kB

bob800 - 27-3-2016 at 17:49

I will venture a guess that this "1000W induction heater" is actually less useful than the 300 watt kit you bought years ago...

Judging by the picture, those capacitors are way too small to be able to handle the kind of currents in a real 1000W induction heater. I have built a ZVS induction heater using the exact same circuit shown here, using about 25 of these kinds of capacitors in parallel to distribute the high current among them, and the most it could do was heat a small socket (i.e. socket wrench socket) to a dull orange. The circuit also had a habit of dropping out of oscillation under heavy loads, drawing a massive surge from power supply and ruining the transistors...

You will also need a massive transformer to provide the 12V-48V @ 20A... I used a rewired MOT and got about 35 amps at 12 volts output. It was a fun setup as a novelty, but I wouldn't recommend it if you're actually heating something for a purpose.

3DTOPO - 27-3-2016 at 17:49

I suppose I might need to use mineral oil instead of water since they could induce current on the water?

WGTR - 27-3-2016 at 21:46

You can, of course, submerge the entire thing in deionized water, so long as the pcb and everything else are very clean. I did something like that here for a lower powered device: https://www.sciencemadness.org/whisper/viewthread.php?tid=31...

I'm not a big fan of the Mazilli-type ZVS switchers because they operate with so little margin for error. If oscillation stops (or never starts) for any reason, then the MOSFETs are almost immediately finished.

If you want to run them in parallel, I'd suggest tying the outputs and the grounds together, and just running one output coil. I'm not completely sure what the schematic for this circuit is, so my advice may not work as-is without some changes.

3DTOPO - 28-3-2016 at 13:30

Quote: Originally posted by bob800  
I will venture a guess that this "1000W induction heater" is actually less useful than the 300 watt kit you bought years ago...

Judging by the picture, those capacitors are way too small to be able to handle the kind of currents in a real 1000W induction heater. I have built a ZVS induction heater using the exact same circuit shown here, using about 25 of these kinds of capacitors in parallel to distribute the high current among them, and the most it could do was heat a small socket (i.e. socket wrench socket) to a dull orange. The circuit also had a habit of dropping out of oscillation under heavy loads, drawing a massive surge from power supply and ruining the transistors...

You will also need a massive transformer to provide the 12V-48V @ 20A... I used a rewired MOT and got about 35 amps at 12 volts output. It was a fun setup as a novelty, but I wouldn't recommend it if you're actually heating something for a purpose.


I don't know how many watts they are actually delivering - but people sure seem to be heating things up with them. On you tube search for ZVS induction heater. They seem to work well - heat things up fast and hot.

Here is a video of the exact same board.

OK, in that video, at 5:41 he is running 378 watts (8.2a @ 46.1v). And the board supposedly goes to 53 volts. Hell - even if they only put out 500w, a few of them together could be really useful.

3DTOPO - 28-3-2016 at 13:34

Quote: Originally posted by WGTR  
You can, of course, submerge the entire thing in deionized water, so long as the pcb and everything else are very clean. I did something like that here for a lower powered device: https://www.sciencemadness.org/whisper/viewthread.php?tid=31...


I was thinking of mineral oil, possibly cooled in a heat exchanger. I wonder how far it could be reasonably pushed? Double capacity?
Quote: Originally posted by WGTR  
I'm not a big fan of the Mazilli-type ZVS switchers because they operate with so little margin for error. If oscillation stops (or never starts) for any reason, then the MOSFETs are almost immediately finished.


Nothing can be done about that I guess?
Quote: Originally posted by WGTR  

If you want to run them in parallel, I'd suggest tying the outputs and the grounds together, and just running one output coil. I'm not completely sure what the schematic for this circuit is, so my advice may not work as-is without some changes.


Do you think trying that would potentially damage them if they do require some changes?

WGTR - 28-3-2016 at 16:33

Quote: Originally posted by 3DTOPO  
I was thinking of mineral oil, possibly cooled in a heat exchanger. I wonder how far it could be reasonably pushed? Double capacity?


If it were me I'd affix thermocouples to the heat sinks to find out. Otherwise I couldn't say.
Quote: Originally posted by 3DTOPO  
Nothing can be done about that I guess?


One might AC couple the feedback to the gates, instead of using the two diodes that currently do the job. The gates could be biased such that both MOSFETs are barely "off" when the circuit isn't oscillating. While oscillating, the zener diodes across the MOSFET gates would keep the gates biased appropriately. To get the circuit to oscillate in the first place, it would be necessary to momentarily raise the bias voltage on one of the MOSFETs to put it into its linear region. This could be done with a pull-up resistor connected to a push-button switch. If the circuit then goes out of oscillation for whatever reason, it should stop drawing current.

Typical Mazilli driver for reference:
mazzilli_zvs-1.png - 19kB
Quote: Originally posted by 3DTOPO  
Do you think trying that would potentially damage them if they do require some changes?


Most likely. I would have to see a schematic of your board.

chemrox - 28-3-2016 at 17:33

Quote: Originally posted by 3DTOPO  
Wow - induction heater technology has really dropped in price (I paid $400 for a 300 watt kit I never got around to assembling a few years ago). Here is a 1000w unit with work coil for $45:

http://www.ebay.com/itm/1000W-ZVS-Low-Voltage-Induction-Heat...

Is there anyway to combine these guys, perhaps with a plurality of work coils operating on the same inductor? Or could they be run in series or parallel? I just need more than 1000w and this would be amazing! Thanks!


what does it do? It looks like a heat sink for a hot board

3DTOPO - 28-3-2016 at 17:49

Quote: Originally posted by chemrox  
Quote: Originally posted by 3DTOPO  
Wow - induction heater technology has really dropped in price (I paid $400 for a 300 watt kit I never got around to assembling a few years ago). Here is a 1000w unit with work coil for $45:

http://www.ebay.com/itm/1000W-ZVS-Low-Voltage-Induction-Heat...

Is there anyway to combine these guys, perhaps with a plurality of work coils operating on the same inductor? Or could they be run in series or parallel? I just need more than 1000w and this would be amazing! Thanks!


what does it do? It looks like a heat sink for a hot board


It is a inductive heater (sans power supply and water cooler), google/youtube search: "induction heater".

3DTOPO - 28-3-2016 at 17:58

Quote: Originally posted by WGTR  
Quote: Originally posted by 3DTOPO  
I was thinking of mineral oil, possibly cooled in a heat exchanger. I wonder how far it could be reasonably pushed? Double capacity?


If it were me I'd affix thermocouples to the heat sinks to find out. Otherwise I couldn't say.



So it is theoretically limited only by MOSFET temperature?
Quote: Originally posted by WGTR  


Quote: Originally posted by 3DTOPO  
Do you think trying that would potentially damage them if they do require some changes?


Most likely. I would have to see a schematic of your board.


I haven’t actually purchased them - just trying to determine if they might be useable. That said I will try to find a schematic, thanks!

3DTOPO - 29-3-2016 at 10:57

Quote: Originally posted by bob800  

You will also need a massive transformer to provide the 12V-48V @ 20A... I used a rewired MOT and got about 35 amps at 12 volts output. It was a fun setup as a novelty, but I wouldn't recommend it if you're actually heating something for a purpose.


1000W transformer doesn't really seem all that massive to me. That said, I plan to use a $20 SCR (to control the voltage) with an inline voltmeter and current meter so it can simply be plugged in the wall.

3DTOPO - 29-3-2016 at 11:37

So I am going to order a couple boards to play with, and see how far one can be pushed with mineral oil, a pump, radiator and fan.

But I've never dumped any electronics in mineral oil before, would this be acceptable?

http://www.amazon.com/UltraSource-501333-Food-Grade-Mineral/...

3DTOPO - 29-3-2016 at 13:31

Quote: Originally posted by 3DTOPO  
Quote: Originally posted by bob800  

You will also need a massive transformer to provide the 12V-48V @ 20A... I used a rewired MOT and got about 35 amps at 12 volts output. It was a fun setup as a novelty, but I wouldn't recommend it if you're actually heating something for a purpose.


1000W transformer doesn't really seem all that massive to me. That said, I plan to use a $20 SCR (to control the voltage) with an inline voltmeter and current meter so it can simply be plugged in the wall.


Actually - I guess I can't just use a SCR - I would need to rectify the AC to DC still. :(

3DTOPO - 30-3-2016 at 00:05

Quote: Originally posted by 3DTOPO  
Quote: Originally posted by bob800  

You will also need a massive transformer to provide the 12V-48V @ 20A... I used a rewired MOT and got about 35 amps at 12 volts output. It was a fun setup as a novelty, but I wouldn't recommend it if you're actually heating something for a purpose.


1000W transformer doesn't really seem all that massive to me. That said, I plan to use a $20 SCR (to control the voltage) with an inline voltmeter and current meter so it can simply be plugged in the wall.


Well I concede - the power supplies are pretty bulky, looking at around $100 per usable KW.

With that in mind, boy, these 15KW beauties is mighty tempting, now going for a quite reasonable $1k (less than what it would cost to combine 15 of these cheap boards with power supplies).

http://www.ebay.com/itm/15KW-30-80-KHz-High-Frequency-Induct...

The manual says it needs to be connected straight to 6 sq mm or better conductor. I have a romex line that is 5.2 sq mm (10-gauge) on a 30-amp breaker. The vendor states 30 amps will do.

But, 30 amps at 240 does not add up to 15 kw. So will I need a 50 amp breaker and 8-gauge wire? Or will it run on 10-gauge wire just a bit warm?

yobbo II - 11-4-2016 at 15:12

Perhaps this may answer some of your questions!

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Twospoons - 11-4-2016 at 21:58

There is a reasonable chance that simply putting the work coils from several ZVS units next to each other will provide enough cross coupling to cause injection locking - and all the units will play nicely together. The coupling drags all the resonant tanks on to the same frequency and phase. Efficiency may suffer a little - make sure your cooling is good.

There's also a chance that all the magic smoke will leak out.

I'd be inclined to give it a try at that price.

violet sin - 11-4-2016 at 22:33

@3DTOPO: "1000W transformer doesn't really seem all that massive to me. That said, I plan to use a $20 SCR (to control the voltage) with an inline voltmeter and current meter so it can simply be plugged in the wall."

wouldnt you have to rectify it AND use a bunch of caps to smooth the AC ripple? I have been doing mainly electronics projects as of late, specifically working on some LED lighting for work, a LM317T adjustable PSU( ~1.5-30V 1.5A) and planning on a much larger PSU (amps increased).

In looking for ways to provide lower voltages at higher amps cheaply, I had the same idea at first. All over ebay 2,4,10,20kW for 2-20$. But at the lower voltages, it appeared to me, they provide fewer amps relative to the voltage (might need a few in conjunction to see the high amps at low volts rms relative to stated kW power out). I mean they are just clipping the AC sine wave to shorter periods and clipping off the tops at times. Reading the rmsV with a multimeter may not give any accurate representation of the true peak to peak V a properly used oscilloscope would. And it is noisy power, has to be tamed quite a bit. Capacitors to drop ripple, low pass filters for harmonic high freq. artifacts, and maybe even an isolation transformer to drop line noise to the rest of your homes electronic devices (dont remember how they do on powerfactor, may need fixing also).

If you have to go through all that, it becomes increasingly expensive to use the cheap low voltage power from SCR's. But that is just what i have gathered of the many hours of.reading, could be mistaken as ive only recently been studying up on the subject, and only in the areas needed. Others here are MUCH more skilled than I in this area. So any corrections on my understanding of the situation are entirely welcome.
-violet sin