I HAVE REWORKED THE CIRCUIT PLEASE CLICK ON THIS LINK TO HEAD TO THE NEWEST CIRCUIT: https://highvoltageforum.net/index.php?topic=46.msg540#msg540

Hi guys,

First time coming here, though I have been in Kaizerpowerelectronics blog before.

Since it will be pointless to make another thread just for the same induction heater, I'm borrowing kamelryttarn's thread to post about my machine. If you don't mind, that is (I'll do another thread if you do mind).

First of all I have to thanks Mads for his advice on using multiple pairs of MOSFETS to deal with high-power circuit. I have made a prototype, and it worked out well:


However, the consumption rate is bad. Even at no load, it consumed approx. 16A for 15.7V input (dropped from 18V). When I put a screwdriver in, the input current rose to  17.47A. Putting in a piece of stainless steel (3x6 cm²) it became 24A. Basically, the wasted energy into heat is just too big.

I assumed that the soldered joints and copper traces burn out a lot of energy, so I decided to redo the circuit (simpler, and wider traces for high-load). Also, getting a bigger work coil.

But for this time, it does not oscillate. I fried 3/4 MOSFETs when it failed to oscillate, and had to redo the circuit (again). Still no oscillation. Just in case, I only make the newest circuit to run under voltage for around a few seconds to observe the problem.

It seems that the input voltage has dropped very low, around 7.5V (from 18V) at 20A consumption. Something must happen badly with the power supply, so I'm posting it all here as well.

The transformer is one I wound by myself. It is very big (enough to be put inside a computer case) and personally I think it can support at least 2kW:

Little final touch:


Assembled with rectifier diodes. You can see below the two square components (the bridge rectifiers) that can deal 1kV-50A each. I used two so that it can work well to 100A (I'm using the transformer at 40A as my aim, btw). To protect the transformer I also added a 20A anti-leakage circuit breaker for the primary coil.


Basically I'm confident that my transformer can support a lot of current even for 18V secondary. I'm, however, doubting the filter I used.

I'm using capacitor-input filter (pi-filter with 1 capacitor bank + 1 coil + 1 capacitor bank) to increase the filtering efficiency. You can see the big-ass coil of 48mH underneath the capacitor bank (actually two banks of around 7000µF each I combined on one circuit board).


I assume that with bigger coil the circuit will need stronger power spike to start up, and with that it overloaded the filter. Do you think that it is the case with mine?

EDIT: To OP: Where did you buy (or find) the choke? I'm trying to find a big one like that but it is hard to get one. If you bought it, how much did it cost? And btw, you are using the two chokes in the induction heater, or they are for the power supply?