Bafang ultra m620 controller burnt

They look like SMT fuses, which would make sense given their location between the connector pins and the P+ (presumably power input), which goes to the B+ (battery positive) line prior to the fuse.

What specifically occured before this problem?

When parts blow up as dramatically as those, typically something fairly severe has to have gone wrong between where they are and system ground or system power to cause it, so just replacing them won't usually make a system work after that--you have to locate the fault that caused the part failure, or the next ones will probably just immediately blow up again. Or they may last just long enough to allow other parts to fail before they do.


A common failure in controllers that can blow fuses, etc., is for the FETs in the phases to fail, as they most commonly fail shorted, and that can be a direct short across the battery positive and negative (B+ and B-).

Things that cause FETs to fail are overheating or overvoltage (which usually happen from a system running near or beyond it's spec limits).

Everything went off on my bike after chain jumping out at full power, I have a second spare m620 (which was working) burnt at the exact same location.
Could my eggrider v2 cause this problem ? That is the only "custom" gadget that was added to stock bike and was running perfectly for a year now in very hard condition (snow, mountain, mud, water, 1500km+)

So, yes it's the eggrider v2 who burnt 3 controllers just burnt my working new one replugging it after using stock one successfully...

pifour...... the Eggrider burnt my controller at the same place as yours! They told me it would "probably" be ok on my bike, so I bought it to adjust the M620 parameters on the fly. I have replaced the controller but the display is showing error codes 10, 11, and 21. I'm searching for a Bafang M620 controller schematic but can't find it.