Hi,
I have been playing with induction heaters based on the circuit attached. And they working pretty good. However I have some issues to figure out the parameters and how it works.
In my circuit I use IRFP4710 Mosfets on one circuit and K58E06 on others, they all see to do the job. Inductors are 150µH all other parts are as in the schematic with the only variables left being the C tank and the work inductor:
1) C = 0.44µF, Work inductor = 1µH
I get 240Khz, 51Vpp / 17.8VRMS from one coil to the other
Power supply gives 1.3A/10V
2) C=0.66µF, Work inductor = 1µH
I Get 197Khz, 53Vpp/18.7VRMS
Supply gives 1.54A / 10V
3) C=1.44uF, Work inductor = 1µH
I Get 133Khz, 51Vpp/18VRMS
Supplyu gives 3.5A/10V
4) 3µF tank, 0.9µH coil
97Khz, 40Vpp, 13.8VRMS
It takes ~5A/10V
These measurements are with no load, once I put a load, lots of things change depending on the what it is (a screw driver, a graphite crucible), it can go up to 10-12A @12V, up to 20-25A @ 20V
What I don't understand is that when I measure the inductor (working coil) with a LCR meter, I get, let's say 1µF, if I put the load inside, the inductance is very slightly changed but nothing to justify hugh power changed in real utilisation.
For example my 1µH Coil show 1.2µH with the screw driver inside and 0.9µH with the crucicle inside. in practice, the screwdriver will make the circuit 4 pump 12A@20V while the graphit crucicle will mek it pump 22A@20V
I have a hard time to understand how to calculate things "in action". What are the ideal parameters?
I have tried to find technical information online but nothing was really clear.
With one of the circuit I have pretty good result melting aluminium in a small crucicle @ ~800°C . Working coil is watercooled (copper tube), and I reach ~20A @ 20V so about 400W. I noticed more caps on the bank means more amps at the same voltage and load but also lower frequency and higher "idle" current, beside trials and errors I'm not sure in which direction to go (I'd like slightly more power at 20V)