Capacity testing NiMH C & d Cell

[ColorMaker]

I have been testing 5000mah C cells and 10000 mah D cells using a cadex c7400er battery anylizer. Cells are tested individually. I set the charge and discharge settings to 1A to achive capacity. The capacity changes when charge / Discharge values change.

Charge / Dischagre set to 1A the battery capacity test at 105%
Charge / Dischagre set to 1.5A the battery capacity test at 98%

I was wondering why the capacity would change I assumed it would be the same.

JM

 

[Mr Happy]

It's normal for the capacity to be reduced when you discharge at a higher rate. With some chemistries like alkaline the drop in capacity at higher discharge rates is dramatic. NiMH does much better at this than alkaline, but there is still a small drop as the discharge rate increases.

It may also be the case that the achieved capacity is slightly reduced when charging at higher rates too, but I think the effect is less.

 

[ColorMaker]

It's normal for the capacity to be reduced when you discharge at a higher rate. With some chemistries like alkaline the drop in capacity at higher discharge rates is dramatic. NiMH does much better at this than alkaline, but there is still a small drop as the discharge rate increases.

It may also be the case that the achieved capacity is slightly reduced when charging at higher rates too, but I think the effect is less.

We are currently testing 10A D cells. We are getting a range of 98%-105%. We use 3 Cadex C7400ER battery anylizers to test each cell individually. all 3 anylizers are set up the same with charge and discharge set to 1A. We get the 98-106 on all 3 machines but I wanted to confirm capacities on the anylizers so I re tested a set of batteries on another machine and the capacities came in higher by 2%. I assume this is due to the second cycle and the battery capacity increased. There may be a 2-3 % diffrence in the capacity testing from anylizer to anylizer so I dont want to mix cells that are tested on 2 anylizers.

What are the effects if I built a pack using a mix of 98% through 105% ? The battery pack is 20 cells (24 volt 10A) We use both a 1.8A and a 4A charger. The drain on the pack is 2.5 amps or less.

JM