I have this 10s5p battery pack.
I kinda banging my head over trying to understand the technical explanation why my battery pack only charges till 40v (and keep going down as time goes by) and the green light shows and then charging stops.
What makes this happen ? The BMS ? If so, why ? it senses the highest cell or P-group voltage and stops ?
Trying to understand things, I’ve read that parallel cells are balancing themselves trying to reach the same potential / voltage levels, so why won’t the pack get balances by itself if all the parallel cells are exchanging current between themselves ?
The BMS (supposed not an active balancing one), isn’t it supposed to do the job and balance the cells / pack eventually ?
If i’ll leave the charger for 2 days connected, will it do anything ? or is it bad.
Sketch of a possible problematic 10s5p battery pack:
If any balancing happens, it’s the BMS or an external balancer doing it.
The cells within each P-group are balanced at all times because they are directly connected together. This isn’t really what the word balanced is referring to typically. But each P-group relative to the others needs to get balanced if it drifts. It won’t happen alone.
There are many different BMS designs. More than we can count. Some balance, some don’t. I personally don’t think there is any utility using the ones that don’t balance, for esk8 construction.
If a BMS doesn’t list a “balance current”, which is typically something like 80mA, then just don’t use it at all. Shop for a different one.
There are also “balance boards” which only balance and don’t provide any under/over charge protections at all, and could in theory be added [to a non-balancing BMS] or used alone.
Yes, most (all BMS are different) BMS will disconnect the charger if any P-group goes too high. (this is good)
BMS that balance will also turn on a balancer for any P-group that goes too high. This just means to verrry slowly bleed that single P-group down a little by making a tiny bit of heat inside the BMS. This is a slow process, as the amount of heat is small.
@b264 thank you very much for the info !!!
Well , I’m not 100% sure which BMS I have since I didn’t build the pack. Do u think it can make any harm if I’ll plug the charger for few days even though I’m unaware of the BMS type ?
I would ask if you have any way to check the voltage of each P-group, but before I even did that, I would check the maximum charge voltage, record that, then let it sit on the charger for a couple days, then check the voltage again. If it’s slowly creeping up, then keep doing that.
BE CAREFUL not to short the pack while checking voltages!
When you edit the question, you may make the previously given answers wrong, or not make sense anymore.
This is a misunderstanding of what a P-group is. The voltage within each P-group (the vertical stacks of cells) CANNOT vary. Not at all. The numbers in each vertical stack are locked together, because the cells are directly connected together, typically with welded nickel.
So you have the whole concept of what a P-group is, reversed. You have ten P-groups in a 10S5P battery, and each one has 5 cells.
(If constructed per that diagram, you’d need five BMSs and you’ve have fifty P-groups, each having just one cell, essentially five 10S1P batteries connected in parallel)
Yes, this is an accurate representation of an unbalanced 10S5P battery. Except typically the one that’s off would be higher than the rest. But either scenario can and does happen.
For this to be fixed, the BMS would have to balance P-groups 1,2,3,4,6,7,8,9,10 and bleed them down to match P-group 5. Typically this wouldn’t happen (but all BMS are different…) until the charge cut off with the nine P-groups all hitting 100% before group 5 did.
Thanks !