Bad Battery or Bad Cell

[Adamsavage79]

I ended up charging it anyway, as I got nothing to lose at this point. The pack isn't really working.

The charger is a 2A charger, and was charging from 5:15pm to 11:15pm. I was monitoring the voltage as it was charging and it wouldn't go past 3.23v to say 3.24v even after 20 minutes had gone by. Starting voltage was 2.30v.

I'm suspecting it might be BMS at this point. I think the BMS has damaged the cell. When it was done charging and the charger still connected and on. The pack was 58.3-58.4v. Most of cells where varying from 3.61 - 3.73. About 45 min later, all the cells expect the 2 that were giving me lower voltage. The cell that is in the same spot as the bad cell was, is 3.34v and the bad cell is 3.28v. The rest of the pack is 3.45 - 3.47. They will likely even out little more later on. Will check the pack in the morning and see what is going on.

I will also try to charge that one cell again to bring it closer with the rest of the pack, and try the same with the one that is reading lower. The two cells in question have only dropped down a tiny bit. 3.33v and 3.27v.
I was looking @ the BMS and I'm not how I would change it. The hardest part seems to be figuring out what wire goes where.

When I was charging the cell, it was out of the pack. So the BMS was not factor.

[Bikemad]

I was looking @ the BMS and I'm not how I would change it. The hardest part seems to be figuring out what wire goes where.

Take a look at this video to see how the balance wires should be connected.
As your battery has twice as many cells as the one in the video, there will be more wires to connect, but they should still connect in the same sequence starting from B- and following the path of the cell connectors.

Alan
 

[Adamsavage79]

His pack is connected different. My pack is one cell is positive, one cell is negative. It does however look like the balance leads are joined at one large plug. I could just unplug that and plug it back in ?

[Bikemad]

All of your cells have a positive and negative ends which are simply joined to each other in series to form a chain of 16 cells. The main difference between your cells and his is that your cells have their (+) and (-) terminals on opposite ends of the cells, whereas his cells had both (+) and (-) terminals located on the top of each cell. The busbars (metal connecting strips) used between each of the cells are connected to form a string of cells in exactly the same way; cell 1 (+) terminal connects to cell 2 (-) terminal etc..

Here is a diagram showing the BMS connections on an early GM 48V battery using 13 groups of 3 paralleled 18650 cells:



The positive end of cell no 1 is directly connected to the negative end of cell no 2, so it doesn't matter whether balance lead 1 is connected to cell 1 (+) terminal or cell 2 (-) terminal as they are basically joined together by the interconnecting plate.

If the replacement BMS uses the same type of connector as your existing one, you may be able to simply plug the existing connector into the new BMS, but check that the new BMS has the same number of balance wires as your battery has BMS connections at both ends of the chain, but some (like the GM one shown above) do not have the two end balance wires on the battery (+) and Battery(-) terminals.

For your battery, a replacement BMS would need to be suitable for 3.2V LiFePO₄ cells, not 3.6V LiIon or 3.7V LiPo cells.

Alan
 

[Adamsavage79]

I have a BMS on the way from Golden Motor via support. I plan to mail the battery to this guy that knows more about battery's than I do. This way if something else comes up, he can fix it. He also has the same cells I use, so if I need to replace a cell, he can do that.

[Adamsavage79]

UPDATE: Bikemad you were right. The BMS wasn't balancing the cells properly which caused a voltage sag. I have the new BMS installed and the pack is still healthy. He said it's a good thing I caught it when I did, or it would of killed the entire pack.

[Bikemad]

It will be interesting to see what the final outcome is, but I'm placing my bet on a faulty BMS.

Ooops, Guess who forgot to place that bet?  Nevermind, at least you were able to fix it without having to spend a fortune on a replacement cell.

It's ironic that the BMS is fitted to balance and protect the cells, yet when it fails it does the exact opposite. 

Hopefully you will have a much greater range now that the pack is being properly balanced again.

Alan
 

[Adamsavage79]

Send me your email, and I will send yeah a coffee ?