My first attempt at building a high-current H-bridge failed miserably. I was trying to drive a pair of windshield wiper motors on a robot with a new H-bridge that I built using discrete MOSFETs (HRF3205) with HIP4081A drivers. I got the design from a Nuts & Volts article. One of the MOSFETs literally exploded. I don't think it was a build problem since my friend built a drive from the same design and tested it completely with a small motor. Two of his MOSFETs exploded when connected to the big motors.
The only thing I can think that would have caused this is flyback voltages that the MOSFET zener diodes did not suppress. I thought that the zener diodes built into the MOSFETs would protect the circuit from flyback voltages (so did the author of the Nuts & Volts article). Maybe these built-in diodes are only effective for small loads.
Am I right about the cause for explosion? If I need to add diodes for flyback suppression, how should I size them? I'm building this drive to handle 20A.
Thanks,
BRW