- Joined Oct 23, 2016
I'm working on building an electric scooter and yesterday the speed controller had a MOSFET failure that I suspect was caused by inductive spiking. This was very surprising to me because I had a schottky diode in parallel with the motor to prevent this type of failure. I took the speed controller apart and tested each of the MOSFETs as well as the diode. The diode was fine and one of the MOSFETs had a short between it's drain and gate. Some of the others appeared to be damaged since their VGD was lower than it was when I installed them. Any ideas on what could have caused this? I thought that the diode would prevent this, but clearly I was wrong. The diode I used is a 1N5402. The MOSFETs are P75NF75s. The speed controller contains 6 MOSFETs and runs at 21 kHz. The motor is a universal and I run it at a maximum of about 60 volts (4 12 volt SLAs in series). The motor has a resistance of about 2 ohms and I measured the inductance to be about 5.6 mH with my LCR meter. I'm pretty stumped so any advice is greatly appreciated. Thanks in advance for helping.