Hello everyone,
I recently bought a GO-FOC G300 for running a large QS hub motor. The G300 has a nice form factor which I like and together with the high voltage and current rating it was a good match for my needs.
Yesterday I had a little incident, because I had earlier connected the ring terminals from the battery to the B+ and B- terminals, and not noticed that the B+ was accidentally in contact with the aluminium housing. So the case was connected to 72V and when I inserted the USB-C cable through the little hole in the case, I shorted the case to the USB connector shield on the PCB which created a spark. Afterwards, the G300 still worked properly with no signs of any defects, but I wasn't able to connect to it from my laptop over USB any longer and the laptop USB port was fine. I took the G300 apart to see if there were any obvious signs of burned components but it looked fine. I plugged in another USB cable to it, measured connection/resistance from the USB-A side connector pins, and to the other side of the 22Ohm resistors (D+ and D-) on the actual PCB that go to the MCU and they were all good. The ground signal was also ok.
So there has been a short burst of high current from the case to the PCB ground plane through the USB connector shield, but all electrical connections are seemingly intact. I'm trying to figure out if there is a manageable way of repairing this. Has anyone had a similar experience or some ideas of how to get it running again or debug further?
Cheers!
For anyone that might run in to a similar problem, I was able to solve it. There is a small 4 pin connector connecting the GND, D+ and D- signal from the small USB connector PCB to the main PCB. As there was a rush of current from the USB connector shield to the minus pole of the battery through the main PCB, the GND pin of the small connector burned. I was able to do a solder bridge before and after the connector and use the unused pin of the connector for GND. It seems that the optional 5V (0 ohm resistor) that is there in the original VESC schematics is not used here. Anyway the USB connection started working again. :)