My battery pack is not Balanced -HELP-

[FourCaesar3]

Hi,

My battery pack 14s8p was desconnected from my escooter for the las 5 months dur to a bms failure. Before the failure I had problems like shutting down the escooter for no reason.
The pack is a 52V and normally when it fully charged, the voltmeter shown 56.4v, and when the voltage reaches 49v, the ebike shutdown.

Now, after changing the bms with another that has Bluetooth function, I can see the voltage pf each string.
The pictures attached shows the voltage.


The problem is the voltage diffrence is above 0,55v and after riding 10km, it becomes 0,33v, and when I plug it again to the PSU, it reaches 0,5xx V again, even With the balancer function is activated.

Do I have some dead cells ? Or I need to balance it? And if a Balance is needed, Can I put the balancer directlly to the strings, even they are connected to the BMS?

Thanks

 

[amberwolf]

What was the specific problem with the original BMS?

The shutting down you had then was more than likely caused by the cell differences--a good BMS should prevent the pack from being used if the difference in cell voltage is this great, because it means they are very differnet from each other in characteristics (capacity, resistance, etc) and are only going to get worse.

Without testing your individual cells it's not possible to know what their actual characteristics are, but it's pretty likely they have this problem, and need to be replaced.

If you just want to use this pack as-is while you get a replacement, you can leave it on the charger until it rebalances; given the differences it's probably going to take a minimum of days, and possibly weeks.



Unless the physical design of your battery / system requires the original pack casing, it's easier and cheaper to buy a whole new battery than to:
-- buy all the building equipment (spotwelder, battery to run it, leads, probes, etc) and materials (cells, interconnects, wiring, connectors) and testing equipment (cell IR / etc tester, etc),
-- gut the pack of all it's existing cells,
-- find a good trustworthy reliable cell supplier and buy enough new cells to be sure you get enough good matched ones out of them to build your pack from,
-- find a good trustworthy reliable cell-interconnect supplier and buy more than enough of them to do practicing with and fix oopsies
-- test them all for matching characteristics so the pack will start out balanced and stay that way for a good long time so you get to use the actual pack capacity, etc. and use just the ones that match (the rest saved for later repairs if necessary),
-- learn how to use your new building equipment (practicing on the old cells from the original pack, or other dead / scrapped cells)
-- assemble the matched cells together,
-- wire up your balance connector,
-- test and verify all the connections and voltages
-- install the BMS
-- test the pack with the scooter.