Jon Elson wrote in message rvers.com...

This can't possibly be right!

Perhaps I've found something new :0 (Yea, I know better, aint gonna
happen!)

2000 uF as a parallel resonator (tank) capacitor?

Yes, and more.. Last run had 10x 0.47uF caps in parallel, also wired
in parallel with the induction coil. For specs on the caps goto
www.digikey.com and search for part number 495-1396

For 25 - 100 KHz?

actually the induction coil was running at just under 150KHz, 80v p-p,
with a very attractive sinusoidal shape.

It sounds way too high!

It might be, but I imagine the induction coil has rather low induction
value as its only 8 turns of copper wire around a graphite core... I
just kept adding capacitors and watched the resonant freq drop until I
got it down below 150KHz. Seemed like the right thing to do

Or, is this
in the DC power supply? If you are burning up the caps on the DC
supply side of the power transistors, it is because you have "shoot
through" currents. That is where both the power transistors in each
half bridge are turned on at the same time. The currents could be a
pulse of 10 - 50 nS width and thousands of amps!

Nope, my DC source for the H-Bridge is JUST two 17Ah 12vdc batteries
in series for 24vdc. (plus two 6 amp battery chargers to try and
recharge between runs.)

You need a MUCH better circuit to control "dead time" between the
two transistors.

The TL494 frequency generator already takes care of the dead time
between pulses. In addition the mosfets in the H-Bridge don't really
get all that hot. Especially now that I have the Tank capacitors
added in parallel to the induction coil AND I set the frequency
generator to match the resonance of the IC tank circuit.

In the end, who knows. My approach to electronic design is along the
lines of "Playing with Legos (tm)" While I have some official
training in electronics thanks to the military, it was a LONG time
ago!

One thing I worry about is my H-Bridge mosfets are rated for 60Vdc
max. I use a 24VDc source, but I measure 80v Peak to Peak across the
inductor - capacitor tank circuit that is being DRIVEN by the
H-Bridge. Will this 80vpp damage my Mosfets? (Hasn't yet...)

Take Care,
James Lerch