taking one or two cells out of a pack

[randomlight]

I have a li-mn 36v 10ah battery that consists of 10 cells . One of the cells is bad but I can`t find a replacement. Would my bms be ok if I just soldered 8 cells together? thanks

 

[heathyoung]

No, the LVC (low voltage cutout) would trip. Unless you can reconfigure the BMS, you are SOL.

A Cell-Log would give you your LVC, but you would need to consider using an RC charger capable of 8S to charge.

 

[randomlight]

Thanks heathyoung,of course that makes sense .So I`am back to trying to figure out how to replace the bad cell.
Could someone tell me what I need to look for when trying to match a new cell to a battery pack.

 

[neptronix]

Your best bet is the find the original manufacturer and ask them for a cell.
If they won't sell you a replacement one, you need to replace them all, since you have no idea who makes the cells.
You can't combine cells of varying C rates / internal resistance in serial without having constant problems balancing.

And your best bet for that would be to find cells that work in the same voltage range ( I think yours are 3.6-3.8v nominal? ), such as RC lipo, NMC, li-mn, li-co etc..

Do you remember what voltage your pack was when fully discharged & what it was when fully charged? because you can use those numbers to select a cell chemistry to go with that will jive with your pre-existing BMS ( if you have one )

 

[randomlight]

Thanks again for a very informative reply Neptronics, I may have to just give up on this, much as I hate to. I found the name of the original manufacterer in china printed on the bad cell. I did try to contact them twice to see if I could get just one cell and also asked for the name of one of their distributors but they will not reply.
The peak charge was at 42.9 and I think the discharge was around 30.I appreciate the help guys but I think given my knowledge of these things I may be out of luck. thanks again.

 

[Ricky_nz]

Try posting a photo of your pack.

Someone may have more information on your pack or have another dead pack that you could harvest cells from.

 

[beast775]

yes try and post a cell,i have a few ni-mh cells around from last year.your lvc seems a bit low? maybe that did a cell in if your running it to lvc quite a bit.a lazy cell might not recover.

 

[randomlight]

Actually I posted a picture of the cell in another post but no one recognized it because I didn`t get any replies from anyone familiar with it .I will put up the photos again here. Thanks so much for your consideration.

 

[randomlight]

so again no one recognizes this cell? So what do I do ? throw away the other 9 good cells? seems a shame really.At least I`d like to give them to someone who can use them...

 

[Red_Liner740]

LOL i could use them! i'm building a slow e-bike for my g/f....lemme know if u do want to part with the pack.

but to try and help you, maybe u can just eliminate that one cell, run BMS-less and use a LVC from a controller or Cycle Analyst? ofcourse u'd lose a bit of top speed and range but it would get u back on the road

 

[heathyoung]

I'd be using something like a pair of Cell-Logs to do your LVC duties, and a cheap RC charger to do the balancing + charging.