Well it seems to work.
I built a fet board up with cheap chinese fets that were no where near spec, and decided we could afford to kill them off........ so i did.
It was impressive with 12 fets blown apart very quickly....... this time there was no sign of stress in the totem pole transistors.... one died quietly, but no cooking or anythinjg else.
I suspect it copped a few millisecs of pain and then died, but did not cause any catastrophic damage....
Rebuilt the board again, and replaced the single transistor on the totem pole.... it was on the side of the fets on both high and low that blew. The high side drivers did not suffer any problems..
So a quick rebuild, replace all the resistors and fets on those two banks...... and then.... pushed it back into service as a transformer and card set on the bench and nothing else. Ran it for 20 minutes at 2kw... and even with poor fets, the heat sinks did not get above skin temp... so it must be running alright, and the wave form must be fairly decent.
Also found out that 2 liters of water in a 2kw jug heats up 45 degrees in about 4 mins.... must do the math and see if thats close .... or the amp meter I used was out.
The unit was doing 225v@8.5A... so was probably a 2400w element running slightly low voltage. Board is a 230v board, and the regulation is fair, and can be improved upon I think. Unloaded was 228v.. so sagged 3v@2kw..... not too bad I guess.
Tomorrow we over load the system big time to see how the lousy fets hold up under 6-8kw... have no idea what they really are.. the print is IRFB4110... but they test out very much worse than that.... instead of 3.5-4.7mohm... they are 7-15mohm... every one is different.
Hopefully it will blow up, but leave the totems unburnt in any way like todays test..... then I will get some confidence that this may be a way to protect the fibreglass
Yes Tom..... were just animals here....
Oh, and 1 transorb 16v shorted so that other bits did not incinerate.
..............oztules