When I first built this circuit it produced a worthless amount of power. The circuit sometimes will not osocillate so all the mosfets burn up. After reading and learning that mosfets need a +12v gate and not +15v like the power supply the circuit works every time now but power is still low. Skin effect is a problem at high frequency I experemented and found 60KHz is much better than 221KHz like the circuit was originally designed. More capacitors lowers the frequency and supplies more current to the LC coil. Then after experementing with different mosfets I learn some are much better than others and why. This is a very educational project I am having FUN and learning TOO. My power supply had to be improved several times now it is 75 amps, 15.3v, with good filter capacitors and better choke coils. A circuit that was originally only 4 amps is now in the 23 amp range, power has increased from about 60w to 345 watts with 2 mosfets. The circuit I found online uses 4 mosfets 150v 100a with 30v power supply video looks good and the guy claims it is 2000 watts.
I have learned just because a mosfet is rated 50 amps does not mean it can run at 50 amps all the time. I have changed heat sinks several times, now I have a very large 3 ounce heat sinks my mosfets get hotter than the heat sink, the heat is just not physically able to transfer into the heat sink as fast as it needs to. The mosfet is producing more BTUs than can transfer to the heat sink even with good heat sink compound and a good clamp. With 23 amps the mosfet is heating up fast and is always about 5 degrees F hotter than the heat sink and a cooling fan cools the heat sink but the mosfet is still hot even with the heat transfer compound. When heat sink gets to about 130 degree F I shut it down and it continues to get about 10 degrees F hotter. If the temperature goes over 150 degree F mosfets explodes, sound like a tiny firecracker Boom, flames shoot out of both mosfets and there is a small cloud of smoke. I notice one of the YouTube videos the guy has his mosfets and heat sink under water, only the mosfet wires stick straight up above the water. There is another YouTube video the guy has his mosfets sandwich clamped between 2 large heat sinks with box fans.
With 3 mosfets in parallel I should be able to use current limiting resistors on pin 3 to find a safe current at maybe 18 or 20 amps or so then the circuit will not over heat and need to be shut down in 2 minutes. I am trying to find the spot where the mosfets will run at continious current and not over heat. Even if I have to limit current to 15 amps each per mosfet = 45a x 15v = 675 watts.
This is just another fun educational learning experience. I do have a use for this induction heater if I can get enough power to heat a 2" diameter steel pipe to 1400 degrees F other wise I will continue to use a 100 ton hydraulic press.