Battery Charge Wire Shorted to Cell? Burned Nickle Strip

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bchaney

100 W
Joined
Jan 2, 2017
Messages
108
Location
Seattle, WA
Well my battery stopped charging this morning, checked the charger and output voltage was fine so I opened up the battery and found this, see pics below. The black wire from the charging port has rubbed on one of the ribs in the case so much that the wire broke. It looks like the wire shorted to a cell or to a nickle strip because it looks like the area got hot at some point and damaged the cell wrap and the strip.

What's the best way to fix this? I got this pack from BMSbattery so I emailed them for help but I don't have high hopes. Do you guys think the cell has to be replaced? Could I add material to the strip or does it need to be replaced too? I don't have the experience or a spot welder to replace the strip... I wonder where I could take it to get it fixed in the Seattle area.

Thanks for any help.

IMG_20170817_180750.jpg

IMG_20170817_180743.jpg
 
Wow, lucky the whole pack didn't catch on fire.

The damaged cell might be still OK if the insulation get repaired. With a short like that, you just get a big spark and the cell doesn't have time to overheat and really get damaged. The nickel strip might be OK just as is since there are alternate paths for the current, but if it was mine, I'd solder a piece of copper wire across it.

If you can clean it up without shorting anything more, you could use a blob of epoxy around the damaged spot to replace the insulation.

Depending on what exactly shorted, you may have damaged the BMS. This might be a bit harder to check. After repairing the broken wire, you could carefully check to see if it charges normally. Also need to figure out a way to prevent it from happening again. I'd use some kind of tape or nomex paper over the whole side of the pack to insulate the nickel strips. You don't want any of those wires in there pinching or rubbing against stuff.
 
That is definitely a "shoulder short", and one of the reasons DIY packs should add extra insulation on the positive tip.

Adhesive%20Cardboard%20Paper%201x%2018650%20Battery%20Insulator.jpg
 
It looks like the black wire made contact with the nickel strip and blew out a part. It took out part of the cell insulation from the plasma ball, but I don't think it shorted on the shoulder to start with.
 
Thanks for the help guys. I didn't make this pack myself, but if I did, those stickers look like a good idea. It's from BMSbattery. I just attempted the repair fetcher suggested, just waiting for the epoxy to cure then I'll try to charge it back up. I really hope this works, this is my first ebike and I've only had it up and running for about 4 months. I had a motor issue and now a battery issue, I'm beginning to think that it's not worth the time and money.

View attachment 1

IMG_20170819_105014.jpg
 
The repair looks good.

It would be a good idea to figure out if anything else was damaged by the short, like the BMS. What connects to both ends of the wire that shorted?

If the charge control FET on the BMS shorted, it would still charge normally but it would not be able to shut off in the event a cell voltage goes too high.

This can be crudely checked by using a voltmeter in diode check mode (or ohms if it doesn't have that feature) and measuring the resistance from the battery negative to the charger negative terminals on the BMS. You have to first disconnect the battery positive and balancing plugs on the BMS. Measure in one direction, then swap the probes and measure the other way. It should behave like a diode, with a low reading in only one direction. If the FET is blown, it will measure zero ohms in both directions.
 
The black wire from the charging port has rubbed on one of the ribs in the case so much that the wire broke. It looks like the wire shorted to a cell or to a nickle strip because it looks like the area got hot at some point and damaged the cell wrap and the strip.
Click to expand...

Thats gotta suck!
 
That's poor. There should be sticky cardboard covers over the whole side of the battery to insulate all the connections.
 
bchaney said:
I had a motor issue and now a battery issue, I'm beginning to think that it's not worth the time and money.
Click to expand...
You have had your more than your quota of bad luck :cry:
 
d8veh said:
That's poor. There should be sticky cardboard covers over the whole side of the battery to insulate all the connections.
Click to expand...

+1

Even a layer of duct tape would be better than nothing.
 
fetcher, the wire that was broken is the one that connects the charging port to the BMS. I checked between the battery and charger negative in diode check mode and I got a reading in one direction but not the other. I just re-read your post and realized that I didn't disconnect the battery positive or balancing plugs though. The battery charged up fine yesterday, though I didn't charge it to 100%. I couldn't find adhesive backed nomex or fishpaper from a US supplier and I don't want to wait for shipping from China, so I ordered some 2" wide 8.5 mil thick electrical tape from Amazon. I plan to wrap up all the cells with that and then reassemble.
 
bchaney said:
fetcher, the wire that was broken is the one that connects the charging port to the BMS. I checked between the battery and charger negative in diode check mode and I got a reading in one direction but not the other. I just re-read your post and realized that I didn't disconnect the battery positive or balancing plugs though. The battery charged up fine yesterday, though I didn't charge it to 100%. I couldn't find adhesive backed nomex or fishpaper from a US supplier and I don't want to wait for shipping from China, so I ordered some 2" wide 8.5 mil thick electrical tape from Amazon. I plan to wrap up all the cells with that and then reassemble.
Click to expand...
Another alternative is a silicon baking sheet (thin flexible sheet of silicon rubber) and you should be able to get those at wallymart.
 
bchaney said:
fetcher, the wire that was broken is the one that connects the charging port to the BMS. I checked between the battery and charger negative in diode check mode and I got a reading in one direction but not the other.
Click to expand...

I think you're good to go. Test is OK with the other stuff connected. Tape you're using is way better than nothing. Fish paper is good because it won't melt and doesn't penetrate easily.
 
Well I got it all wrapped up with the heavy duty electrical tape and back in the case. I'm noticed it had a couple sticky foam strips to hold the cells away from the sides of the case, but they were unevenly distributed and crooked. I replaced them evenly, hopefully that will help.

Took it for a test ride today and it seems to be working fine. I guess only time will tell if that cell craps out early.

IMG_20170824_184642.jpg
 
IMHO i would not be sleeping in the same house with that battery or riding it. There are no paper insulation gaskets on the positive electrode, and it's not possible to determine the totality of what has happened to the cell when it was shorted. I took me a few days to build my battery and I added extra insulation in between cell groups. The pack accumulates lot of vibrations over time. Just my opinion. Everybody has one :)
 
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