NiMH 24 volt back builing

I have been testing 10A D cells to assemble battery pack. I have altered my testing methouds to increase volumes.

I first put the D cells on Condition mode in the MAHA C808 charger which requires 24 hours.
I then put them on a Cadex 7400ER battery analyzer to get the capacity of the individual cells.

The cells are ranging from 99% to 105%. Once I have a full bin I assemble the cells into 6.0 volt bacls (5 cells). I then put the back on the cadex analyzer. The pack does not test in at the same capacity. Pack build with 101% cells test out at diffrent capacities from 98%-102%. Should I ignore this PACK test and just assemble cells that tested from the same capacities ?


JM

Maybe you are within experimental error? It's very hard to get measurements more accurate than 3% without rigorous laboratory conditions and test protocols.

ColorMaker said:

I have been testing 10A D cells to assemble battery pack. I have altered my testing methouds to increase volumes.

JM

Click to expand...

CPF members bwaites, js, and luxluthor may be able to give you some insight. They have plenty of experience when it comes to what you are doing.

D size NiMH cells have pretty high capacity. Assuming you go through the various concepts for optimizing them, such as multiple low current charge / discharge cycles to "break them in", then I am not sure if you can do this in just 24 hours - but maybe.

The people that really optimize packs match not only the capacity, but the shape of the discharge curves at the desired current.

One of the tricky things about assembling a pack from NiMH cells, is that invariably, they are going to be at different states of charge when you build up the pack - no matter what. In the LiPo world, they add balance taps between each cell. Getting the cells exactly balanced would require at least some level of balancing as a pack as well. I think the usual method is to charge the pack really slowly when you are finished.