Help Paralleling Lipos

rg12 · Sep 7, 2021

I have 9pcs 7S packs and need to connect it to a 21S 3P.
The question is, if I connect 3 sets of 21S, then I need to parallel everything.
Can I parallel just the first negative and last positive wires of all 3 groups?
Bare in mind that I'm connecting them to a BMS and will have balance wires paralleling each cell individually to the same cell number in each 3 groups.

markz · Sep 7, 2021

Batteries have to be within 0.01V when paralleling.

As far as the BMS goes, since the lipo's themselves dont have a bms but do come with balance wires, you want one overall bms, with all 3 parallel batteries balance wires connected in parallel. Probably not a good thing to add another factor (the bms) to lipos, probably best to buy 3 balance chargers to balance charge the 3 batteries you will have in parallel and buy balance chargers with enough power
1) overall bulk charging power
but also 2) balance power (iChargers, Tenergy, Hobbykings Turnigy)

rg12 · Sep 7, 2021

markz said:
Batteries have to be within 0.01V when paralleling.

As far as the BMS goes, since the lipo's themselves dont have a bms but do come with balance wires, you want one overall bms, with all 3 parallel batteries balance wires connected in parallel. Probably not a good thing to add another factor (the bms) to lipos, probably best to buy 3 balance chargers to balance charge the 3 batteries you will have in parallel and buy balance chargers with enough power
1) overall bulk charging power
but also 2) balance power (iChargers, Tenergy, Hobbykings Turnigy)

I have to have a bms to cut power to avoid depleting or over charging.

I have done this before with 8pcs 5S connected as two parallel units of 4 packs in series but in that situation it was easy enough to parallel the packs not just with the first negative and last positive as suggested here.

docw009 · Sep 7, 2021

I'd worry about lateral currents. Why not use a heavier wire to cross at the balance points, not a balance wire. 16G wouldn't be too hard would it? There wouldn't be lateral currents in the ideal world, but if one set of 7S is mismatched, one end of a parallel group might sag.

j bjork · Sep 8, 2021

I have done it before without problems. If your cells are ok you dont need thick parallel connections.
20s3p on the "bomber"

motomech · Sep 8, 2021

Well, since you have done this before maybe you can teach us something.
I would be curious how you charged your 20S 3P BMS equipped packs?
Thank you in advance

j bjork · Sep 9, 2021

I used a server psu trough the nucular controller.
So I set the voltage I want in the nuc.
But just use any charger you want that does the job, or is it something else you want that I am missing?
Just charge like any other lithium pack.

Help Paralleling Lipos

rg12

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