I built several induction heaters based on the popular ZVS module available everywhere.
They all work fine with a 20mm coil diameter.
But the performance improve drastically with a 12mm coil diameter ; The problem is that the modules fail, but in a very peculiar way : When activated, 4 times out of 5, everything is OK, the control LED shines brightly, and the heated element gets to the desired temperature (around 220C) very rapidly. But 1 time out of 5, the LED seems to flicker very rapidly and faintly, and if the current is maintained, just as no heat is produced by the coil, one of the two MOSFET burns.
If, at that time (right when I see the LED flicker) the current is stopped, everything is fine, just press the switch again, and it works.
Note that I'm using heavy gauge wires and switches, just to eliminate those as a potential point of failure. I'm using 12V / 5A PSUs.
I tried shortening the coil wire to reduce the number of turns, but the problem persists.
How can I solve this problem, or turn around it? How can I at least make the ZVS module fail safely?