25 ah 3.2 volt cells-Mixing

chrisski

Solar Boondocker
Joined
Aug 14, 2020
Messages
2,704
I am mixing Topband 3.2 Volt Cells with different capacities into a single 8S Battery. There's about a 6% difference in capacities in the cells. I wonder what will happen?

-Three are capacity tested at about 24.7ah. They are the blue wrapper ones from BatteryPlus, now sold out.
-Five are Capacity tested at 26.3 amps. They a green wrappers saying Navitas.

Factory Specs are exactly the same on both Cells. I'm glad I learned that with this smaller cell pack before building the bigger battery at 280 ah with Eve Cells.

The learning will really come when this battery is finished and is put in parallel with another 8S 25 ah pack where the 8 cells tested out around 24.7 amps with a 2.5% difference.
 

FilterGuy

What, me worry?
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Nov 26, 2019
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Location
Los Gatos CA
I am mixing Topband 3.2 Volt Cells with different capacities into a single 8S Battery. There's about a 6% difference in capacities in the cells. I wonder what will happen?

-Three are capacity tested at about 24.7ah. They are the blue wrapper ones from BatteryPlus, now sold out.
-Five are Capacity tested at 26.3 amps. They a green wrappers saying Navitas.

Factory Specs are exactly the same on both Cells. I'm glad I learned that with this smaller cell pack before building the bigger battery at 280 ah with Eve Cells.

The learning will really come when this battery is finished and is put in parallel with another 8S 25 ah pack where the 8 cells tested out around 24.7 amps with a 2.5% difference.
If there was ever a time to top-balance, this build is it.

If you do a good top balance it will work reasonably well, but the battery capacity in Ah will be defined by the weakest cell.


 

chrisski

Solar Boondocker
Joined
Aug 14, 2020
Messages
2,704
ThanIs. I’m finishing the top balancing now. The last cell is on the power supply after the capacity test.

So looks like this second battery will have a capacity of 24.6 ah since that is the weakest cell. I was thinking differently at first, but with the BMS, that will shut off at the lowest cell voltage.

Don’t think I explained well in the original post that all 8 of these cells are Topband 25 ah cells. Side by side they look exactly the same expcept one has a blue wrap, and one has a green wrap. I believe those cells were the same part made by the same factory in china, except at different times for different distributors.

These aren’t physically different cells but stamped with the same capacity I’m trying to make a battery out of. I’m not that brave.
 
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