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--- 2593519
Do I really need a BMS these days when charger modules are so cheap I can have one dedicated for each individual cell in the series pack?
--- 2593526
>>2593519 (OP)
these dont talk to each other though, so it won't take long for one cell to become unbalanced
--- 2593571
>>2593519 (OP)
Yes, if you want to spend the money you spent on your cells efficiently. Otherwise many won't be charged/discharged ideally and will need replacing sooner too
--- 2593592
>>2593526
>modules charge each cell, independently, to the same voltage
>modules discharge each cell, independently, to the same voltage
>unbalanced cells, somehow
The real issue is that each cell would have to be charged on an isolated circuit, since tying-up the module inputs would short the pack.
--- 2593660
>>2593592
How would the input to the charge module short the pack?
--- 2593720
>>2593660
Input (-) to OUT (-) is a straight trace. Red arrow is how the cells short, green arrow is how the charger also shorts.
--- 2593721
>>2593720
So add some diodes
--- 2593787
>>2593721
Ignoring the voltage drops they would cause, where do you plan to place these diodes, chief?
--- 2596503
>>2593787
he means like this for sure
includes no shorts, overpower protection, reverse polarity protection, etc...
--- 2596863
>>2593519 (OP)
Just add a switch to make all batteries in parallel so you can charge them all with one charger, then switch back to all in series
--- 2596893
>>2593592
Yes, and? 
The cell with the lowest capacity/highest resistance will go empty first and the pack turns off
Whereas with an active balancer you could have used the rest
--- 2598671
You need to put a switch between each cell like picrel so it would be possible to charge each cell separately.
--- 2600321
>>2596503
>no shorts
Wrong. Red arrow is still a short.
Also; the diodes block any charging current from reaching the batteries.
--- 2600364
Are the battery nerds here?

Got this garbage picked 40V Ryobi pack. Recovering the cells. It’s basically two 18V 4.0Ah packs in series.

Charged up the one half, got the cells >2.5V and they all seem to be holding after a couple days. The second half I’m tossing on the power supply randomly to see which sets charge.

So it’s 5s2p on each side, and two rows of the 2p’s seem to be dropping back to near zero the next day after feeding them some power. So do I have 2 dead cells or 4 dead cells? Like if one cell in parallel is trash, is it going to brick the cell paralleled with it? Or if I cut them apart, is there a chance one of the two cells is still good?
--- 2600792
>>2600364
Cells in parallel work like a single bigger capacity cell. In a parallel connection both cells will be on the same voltage.
There is the chance one of them on each row is dead and the good one is constantly discharging on the dead one and that might've damaged the good cell overtime.
Either way, the best bet you have is to crack it open.