Adding different cell to fix a battery

[aaronlim]

One of the 13 cells of my 48v15AH battery died so i ordered a replacement from bmsbattery. However the new cell is a different cell (High C-rate) from the ones that came with the battery. The battery was ordered 3 years ago, but its seldom used so i wanted to attempt to fix it. It does not have a BMS but i was managing it quite well until my wife forgot to unplug the controller and left it there for 3 weeks.

My question is can I use this new cell to replace the dead cell? How well will it balance? They are all 15000mah cells, but the new cell is slightly narrower than the rest of the cells and its ofcourse a High C-rate. This battery i intend to use as a spare. I would like to know some pointers or tips whether i should carry on with this surgery. BMS battery do not seem to sell the old cells anymore

OLD CELL:

NEW CELL:

 

[dnmun]

if you cannot balance the pack during charge because there is no BMS then the pack will not charge each cell up equally because they do not have the same internal resistance. if it totally discharged with no BMS to protect it then i doubt if the other cells in the pack are better off than the one you scrapped. why would BMS battery sell you a battery with no BMS to begin with. that should be illegal and i have never seen other battery makers sell a battery without a BMS.

 

[aaronlim]

if you cannot balance the pack during charge because there is no BMS then the pack will not charge each cell up equally because they do not have the same internal resistance. if it totally discharged with no BMS to protect it then i doubt if the other cells in the pack are better off than the one you scrapped. why would BMS battery sell you a battery with no BMS to begin with. that should be illegal and i have never seen other battery makers sell a battery without a BMS.

The battery came with a faulty BMS which was replaced with a new battery. This battery was then for me to play around with. The other cells are right now at 3.65v, the new cell is 3.71, i intend to balance them again and limit to 53.3v total charge. My only concern is the internal resistance of the cells vs the new high c-rate cell, but since this battery is seldom used, the 12 other cells i believe are still in good condition. How well will the balance of the cell hold? Or would i need to rebalance the cells every week or something?

The dud cell was at 0.3v and its super bloated (didn't explode or catch fire though)

The alternative is for me to convert the battery to a 12s 50v with the remaining cells but that would mean i have to adjust the charger voltage and have different chargers for 2 different batteries which i don't wish to do.

 

[dogman dan]

You can use it, but I believe it will tend to need a balance every cycle if it's really that different in resistance.

Worth your while to just test a few cells, and see just how different the resistance is, then try it. Worst case, you just have to do lots of balance charging it. If the rest of the pack is that old, you may be at that point for those cells anyway.

 

[dnmun]

why not use the BMS you said is faulty? that will keep the battery balanced. unless you did something to damage the BMS i doubt if there is anything wrong with it. of course if you had just fixed the BMS problem then the pack would never have been ruined.

 

[DrkAngel]

Rebuild pack with new cell.
Balance charge pack at 4.10V (Li-ion - Lion setting on many balance charger) Monitor cell voltages during initial charges!
Do a reasonable discharge (50% - 3.80V?) at very gentle rate. (12mph?)
Compare cell voltages.
Normal, monitored, recharge - compare recharged voltages - balance if necessary.
Do a reasonable discharge (50% - 3.80V) at very heavy rate. (24mph?)
Compare cell voltages.
Normal, monitored, recharge - compare recharged voltages - balance if necessary.
Repeat tests at deeper discharge depths ...
If tolerably equal, cells match reasonably and balance charge required only occasionally.

Object is to compare cell voltages at various discharge rates.
Ideally, new cell will not discharge as deeply but recharge to same equal voltage as other cells.
4.10V recommended as added safety margin for any imbalance and as a way to double pack life cycles.