How To Find One Bad Cell In A Lithium Ion Battery Pack - Fix BMS Low Series Voltage Cutoff

Balancing A 48v / 20aH Lithium Ion Battery Pack After Storage (and How to Find That One Bad Cell)

If you've noticed your charger isnt getting your battery to full voltage, it's probably because one of your series is way low or high in voltage compared to the others, and your BMS is cutting out to protect the pack.

Here we're going to learn a bit about how to resolve this issue, especially in a pack like this that has been stored for a long time.

[JoshuaWShanks]

I wanted to thank you for making this video! I've been troubleshooting a battery pack on an electric scooter and couldn't find anything specific like your video. It's a 13S4P 48V pack and the BMS wouldn't let it charge. One of the cells was testing 0.856 volts and I was wondering if you could in fact charge an individual cell with a power supply. Awesome info!

[JamEZmusic]

Honestly this video helped me so much. When the video got to the end while I was watching it on the tv I couldn't find it again no matter what I searched for, only by using the computer upstairs and looking at the "history" was I able to find it again. You deserve a lot more views.

I got 2 really helpful tips from this video.
1:Isolating the cells from each other by just removing the nickel from only the positive side (I never thought of this, I was going to strip from the back also)
2: those actual numbers and what to shoot for when charging.

I have a power supply turning up tomorrow, it looks similar to what you are using, I am hoping I can bring all my series sets up to within .02V of each other. What settings would you suggest to use if I was going to charge just 1 cell up to around 4.1V so it matched all of the others? How many amps would be safe to use?

I didn't realise you could charge the individual series up while all the nickel was still attached. And I still can't get my head around how the charger can pinpoint just that one parallel group even though every cell in the battery are welded together with nickel. But i'm just glad I do not need to strip it all down (unless a cell is knackered)

Can i disconnect a BMS board by just removing the negative wire that is attached to the 1st set of parallel cells to the B- terminal on the BMS board? would that be good enough to "bypass the BMS board to allow me to charge up the battery as normal using the normal charger for a bit to bring up the average voltage of all of the cells?

Sorry for all the questions. I have an E-bike battery here that is damp inside and some rust has formed on a few LG cells which are testing below 1V, so I was not even going to attempt to revive those and I have since ripped them out but the rest of the cells are still fairly high on the same series circuit (3.6v) and I think those are probably going to be ok. The guy must have been riding through a deep flood for that kind of water ingress... but nevertheless. I would like to try my best to bring it back up to perfect health. And if I can't, there are many good cells in the battery for good use anyway.

All the other 75 or so cells are measuring at 4.11V, so I feel pretty confident it is only the 1 or 2 cells that are corroded and knackered from water damage. Hoping the BMS is not knackered.

Cheers for the awesome vid

[fleity]

Thanks for the video. I have a similar situation in my eskate board battery pack. The pack only charges to 89% and cuts out rather early. I suspect that there is one bad cell in it. Since I didn't build the pack I don't have access to more cells of the exact same kind. Since you said you would probably replace the faulty one after you found it do you have any advice on what cells to look for in such a case? Same brand, same type? but the batch obviously can not be the same. Similar age, usage, capacity, internal resistance but different brand?

[michaelshurts]

I have my 72v battery all taken apart thanks to you. One set of cells on mine are reading 3.0 volts all others measuring 3.9. Do those need replaced? I already have them pulled out so will be easy to fix

[Busabuck]

You are using an inductive load across a dc source to discharge the higher parallel group. Would that not be a short ?

[shafiullahislam]

How many pieces of cells is it made of?

[niacalnia]

Is the voltage low on the series or parallel packs?

[marcusmarin]

What if some of my cells are 4.5 volts ?