Symptoms of Damaged BMS?
So in my haste and excitement to charge my battery pack and get it rolling, I decided to wire up some connectors rated for 12v on a 48v battery pack and got a nasty lesson in dielectric strength. The charge connector completely shorted out and spot welded itself shut. After that I soldered in some XT90 connections and now it charges but whenever I'm riding the ebike will just shut off. While under minimal load (using Bafang C965 display), and no throttle, only Pedal Assist. I'm curious if I blew the BMS.
Unplug the battery and plug it back in and the display turns on. The battery pack doesn't even get mildly warm.
It's hard to say. This can definitely be a symptom of a damaged BMS, but other issues can also cause this. Generally, shorting the charging wires usually only damages the charging circuit on the BMS but when surges of current flow through sensitive electronics, unpredictable things can happen.
Last time I shorted the ends of battery cables, the symptoms of a damaged BMS included several chunks of missing material from the FETs, and a distinct smell of burning plastic. It wasn't real hard to diagnose, as I had just essentially welded the ends of two wires together. Ka POW!
Since then I have been VERY CAREFUL when working on battery wires. In many packs, there is a fuse. REMOVE THE FUSE. In many packs, there is a center-of-pack disconnect. OPEN THE DISCONNECT (my old pack had a bullet connector as center-of-pack disconnect.) Once the center of pack disconnect is open, COVER IT WITH ELECTRICAL TAPE. Worse comes to worse, have a friend hold the bare terminal while you WRAP IT WITH ELECTRICAL TAPE. all these measures are designed around the principle that you must only have one bare terminal wire at a time while working on battery connections.