As I was accelerating across a road in my S-10 EV, I heard a pop, and I lost power. I was able to coast to the side of the road, and use my small “glovebox” multi-meter to determine that the HV fuse was blown. The real question was why did it blow?
Given that the leads from the batteries were still providing 128 volts, the fuse probably blew because the motor or controller had drawn a lot more power than they were supposed to. With the advice of members on the EVDL, I was able to use a 60 watt lightbulb connected to some lamp cord to determine that the controller was not shorted and appeared to work.
Specifically, I replaced the fuse with the 60 watt lightbulb, disconnected my motor from the controller, and turned on the keyswitch. The lightbulb lit up as the capacitors in the controller charged up. It was supposed to turn off after this if the controller wasn’t shorted open, but it didn’t. However, I then realized that my DC to DC converter was in the circuit and drawing power, explaining why the lightbulb had stayed on.
I pulled the fuse to remove the DC2DC converter from the circuit, and then the lightbulb would light up as the controller charged it’s capacitors, and then go dark once the current stopped flowing. This meant that the controller was not immediately blown and shorting upon startup, but I had to test if it would short when activated.
So I replaced the high voltage fuse with the spare in my glovebox, and left the motor disconnected. I placed the 60 watt light bulb where the motor would be connected, and then powered up the system. By using the “go” pedal, I was able to use the motor controller to power up and control the voltage and brightness of the lightbulb. This showed that at least under low loads the controller was working correctly, so I moved on to diagnose the motor. (See my next post for that…)
As things turned out, the controller WAS the source of my problems. Apparently, some number of the MOSFETs inside had shorted out, destroying themselves and causing my fuse to blow. When I tested it with the lightbulb, the destroyed MOSFETs were no longer shorted (it’s hard for something that exploded to maintain a short), and the controller was only”working” on a few remaining MOSFETs. (Plenty to control a 60 watt light bulb).
But, since I didn’t know that yet, I continued on to checking out my ADC FB1-4001A motor.