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imsmooth

Senior Member

Joined: 07/02/2008
Location: United States
Posts: 214

Posted: 08:15pm 02 Jan 2010

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I just built and induction heater, and you can see it in action here.

If you want to read all about them, I just put together a tutorial here.

oztules

Guru

Joined: 26/07/2007
Location: Australia
Posts: 1686

Posted: 10:39pm 02 Jan 2010

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Simply brilliant Imsmooth.... as always.

in awe....

......oztules

Village idiot...or... just another hack out of his depth

Dinges
Senior Member

Joined: 04/01/2008
Location: Albania
Posts: 510

Posted: 11:15pm 02 Jan 2010

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Again, impressive, Jonathan.

The power of eddy currents at work....

An inspiration to get on with my own heater. Considering what 65-70W (modified PC PSU) could do, I'm really looking forward to what the present 1kW project could achieve. And after that....2-2.5 kW is the goal! At present, the 1kW inverter is nearly finished - gate drive circuit will be next.

Any more modifications/improvements you intend to make to your design/circuit? Things you would do differently next time?

Peter.

imsmooth

Senior Member

Joined: 07/02/2008
Location: United States
Posts: 214

Posted: 04:55am 03 Jan 2010

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I am trying different toroids and turns. Right now I have determined that the powdered toroid works better than the ferrite toroid. The ferrite has more ringing when off resonance, and has slightly lower power transfer.

I am going to connect my HV line to my 40A circuit when I have a chance and see how high I can crank it. I will probably have to split the rectifier into two for my voltage doubler as the one 25A rectifier will not handle all the amps.

How did you like all the oscilloscope tracings?

Dinges
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Joined: 04/01/2008
Location: Albania
Posts: 510

Posted: 09:42pm 03 Jan 2010

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Scope waveforms and the explanations that go with it are excellent and very much appreciated. Especially the phase relationship at resonance was interesting - hadn't seen it explained so simply before.

The series zeners (5V1 at the gates) are new to me too. I wonder if the same effect could be achieved by using a larger gate resistor? Because the zeners will always drop 5V.... and if your gate drive transformer (GDT) puts out 15V, the FETs will now see only 10V of that.

Only thing I would add would be the anti-series zeners (2*15V) over the gates to suppress any spikes; I know you don't have any spikes now.... but zeners costs cents and may save the FET in case of problems.

But could be a difference in philosophy... I'd want my heater to operate reliably and survive any abuse (including running without a load) - I know myself too well, sooner or later I'd do something that would damage the machine, unless it was protected against user stupidity. Same with the diodes to fully isolate the intrinsic body diode of the FET... I'm using old FETs.... and there's always the possibly that, due to a defect/problem in the control circuit, it would lose lock and starts driving the tank at a frequency below resonance. I'd rather not have that cause the FETs to fail. Murphy and all....

I hear different opinions on using ferrite or powdered iron toroids. Interesting to see you are having more succes with powdered iron, as the majority of people claim you should use ferrite - only exception being neon-John.

Have you tried running the machine unloaded, to see if it would survive?

Peter.Edited by Dinges 2010-01-05

imsmooth

Senior Member

Joined: 07/02/2008
Location: United States
Posts: 214

Posted: 12:53pm 06 Jan 2010

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Dinges said
Only thing I would add would be the anti-series zeners (2*15V) over the gates to suppress any spikes; I know you don't have any spikes now.... but zeners costs cents and may save the FET in case of problems.

I hear different opinions on using ferrite or powdered iron toroids. Interesting to see you are having more succes with powdered iron, as the majority of people claim you should use ferrite - only exception being neon-John.

Have you tried running the machine unloaded, to see if it would survive?

Peter.

I think I will add the anti-zeners to the schematic as they are a simple thing to do.

I am buying another powdered toroid for a total of 4 to see if this improves coupling. I am also getting an equally sized MgZn ferrite 1khz-1Mhz range and see what this does. The ferrites I experimented with were from Ebay and I don't know their composition.

I have just wired a 40A line. I am looking into getting a larger variac for either 120 or 250v service, and push the unit up to the voltage max of the chips.

KarlJ

Guru

Joined: 19/05/2008
Location: Australia
Posts: 1178

Posted: 08:56am 14 Jan 2010

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Pharq!

I knew there were some cluey guys here but WOW.

Did you know you can buy an induction stove?

perhaps a worthy day to day use for this otherwise limited use (unless you are a jeweller) for this thing

Luck favours the well prepared

imsmooth

Senior Member

Joined: 07/02/2008
Location: United States
Posts: 214

Posted: 03:34am 19 Jan 2010

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I have started work on induction heating levitation. I can suspend the workpiece in a magnetic containment field and melt it down into a glowing ball.

Here is the video. If you go to my page I have one with melting copper in the field.

I plan on writing an addendum to my induction heater tutorial that includes how to make the levitation coil and power requirements.

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