I've took a look on the controller today.
It has the main cap(100v470uF) slightly puffed and the legs melted, one of them was totally disconnected.
But there is another smaller (100v100uF) after the shunt that seems OK.(reverse polarity blew the shunt).
I have separated the ignition wire and powered up only that part without the FET rails, and the voltage regulation seems fine.
Battery was at 61.xv, and the power resistors dropped only 9.3v (480 Ohms). This equates to 19mA a little low, I know that when everything is connected, motor included it should be somewhere around 60mA. But there was nothing connected and the FET rail was disabled.
I'm not sure what is the LM317T topology on this 6FET controller, it does not see the full 61v-9.3= 52v, was only about ~40v and 1.2v across the leads, but the voltage reading on 7805 was 12.18v and 5.07v respectively, so I think the voltage regulation stage should be fine.
I have tried to reprogram the microprocessor and it worked, so it should be fine.
At this point the main cap needs to be replaced.
But still don't get what happened second time. Replaced the shunt and the blown FETs.
If I remember correctly I have powered up the controller with everything hooked up (and probably blown main cap, could not see that because of lot of wires there) and throttling it did not move the motor. Probably tried this twice. If I remember correctly the wheel was still rotating without resistance by hand.
Than I introduced a thin wire at the battery hookup in case something goes wrong and next time I powered it up, blowed this little wire in a big spark, and I found the wheel has resistance again and after measuring them I have 2 low side FETs and 1 high side (one on every phase) shorted this time. The polarity was OK, I have double checked. Shunt is Ok.
I still have 5FETs, so I can replace these ones, but if I kill again more than 2, I am left without controller.
I was thinking to get some cheap FETs locally, just for testing and troubleshooting this. But could not find anything above 60v (18sLiFePo4) with reasonable current rating. What FETs would you suggest? What 75nxx FETs are the chinese controllers using?
I also have a spare 6FET board, maybe the best idea would be to just migrate everything on that...Trying to troubleshoot this could just make more damage.
fechter said:
If the gate drivers are shorted, the FETs might be on when they are supposed to be off, causing shoot through and destruction.
If you measure resistance from each FET gate to ground and to the 12v supply line, you should not see anything that looks like a dead short.
I will have to check this, if I don't see any short here can I assume everything is fine? Still not sure the blown cap is the only problem...