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Balance Li-ion Cells Before Connecting BMS?


#1

@chaka
@torqueboards
Does anyone know if it’s beneficial to balance your cells before building the pack and connecting the BMS? Or will the bms take care of that during the first charge?


#2

Can’t do that, the cells are already in parallel, you would be taking the same measurement 4 times.


#3

Wow, good point, brain fart.


#4

Just make sure they are all about the same in voltage before making the parallel connections.


#5

It wont hurt to balance them first. I probably would.
that way you know they are all around about the same voltage when you start. saves you from measuring each individual cell.


#6

Doesn’t the BMS balance all the cells the first time you charge it up?
Doesn’t the BMS balance every cell every time you charge the pack?
Doesn’t it also discharge all cells equally?
I thought that was the whole point of the BMS.


#7

if you are assembling a battery you would probably be connecting the parallel cells and spot welding them in place well before you have hooked up the BMS. un balanced cells being connected together in parallel will equalize themselves rapidly, causing large current and possibly cell damage. its best to bring all the cells to the same potential before connecting them.


#8

do you recommend charging each cell full or storage charge before building the pack.


#9

I don’t think it matters too much if all the cells are balanced.
I’d prefer storage voltage before building a pack because it may be slightly safer.


#10

According to lowguido, it does matter when building parallel packs.


#11

I think storage voltage would be better too. As long as they are all the same voltage of course.


#12

And what needs to be connected first? Power wires or balance wires? Always forget this.