2 packs in parallel at the cell level

transposon

100 W
Joined
Nov 24, 2011
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192
Location
Massachusetts
I have 2 packs that consist of 2 7s packs each connected in series for discharge and parallel for charge.

pack 1 - samsung 25R
7s 6p
7s 6p

pack 2 - salvaged laptop cells
7s 6p
7s 6p

Would it be OK to connect the two packs in parallel 14s6p + 14s6p for longer trips? I can connect at the p group level since I don't have a BMS on these cells. Since the 25Rs are much higher current batteries, would this be a bad idea? Would it be better to connect in parallel just at the pack level (no balance leads)? All of the parallel groups are close AH wise.

My worry is that there may be high currents flowing across the balance leads between the 25R and laptop cell groups due to the large difference in internal resistance/voltage drop. I will not be pulling a lot of current from these packs. Probably 6-7A continuous.
 
2-6p packs paralleled at 6or7 amps continuous

thats 12p
do you mean
12px7=84amps
or
2 packs each at 7 amps continuous
for 15 amps

you could put a fuse on the laptop cell pack
its higher resistance

that way if the packs drift too far apart the fuse will blow
 
it would not be much of a problem. but i would ensure that you use an acceptable wire gague to connect the groups. at full load you might see more current flow between them then what regular balance wires might be rated for.
 
flippy said:
it would not be much of a problem. but i would ensure that you use an acceptable wire gague to connect the groups. at full load you might see more current flow between them then what regular balance wires might be rated for.

Good idea flippy. The balance leads are 20awg. Do you think that would be OK?
 
transposon said:
Good idea flippy. The balance leads are 20awg. Do you think that would be OK?
if its -actual- copper and not CCA then it should be fine for light applications.
 
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