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Actually, I'm very confident that the mosfets were breaking because of a floating gate. I added a resistor from gate to source, and now it's fine. Turning on the power section before the control section creates a high voltage difference between drain and source. The mosfet was turned on because the floating gate was above 4v relative to source. Basically the mosfets got shorted, and the current limit was exceeded, causing them to fail in a shorted state.
Those 200v 60 amp diodes have a very fast response time (20 ns). I'm getting voltage spikes of only about 4 volts when I run the controller at 72v. I have been using freewheel diodes. I'll use about 10 or 12 of them in the car's version. That will allow for a current of 500 or 600 amps, and a voltage of around 144v, with voltage spikes of around 5v or so. The EVTech list has suggested the components I'm using, including filter caps, mosfets, diodes, etc..., and there are working 144v 600amp controllers made by people on that list that are using those parts.
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