I finally got around to doing another bottom balance. The goal was to confirm my instrumentation readings and to verify that the batteries had stayed balanced over the course of 11 months and almost 11,000 miles of driving.
First, I drove until my LinkPro indicated almost 180 amp hours. I did reset my trip odometer after charging, so I was able to drive 72 miles on a single charge.
Then I used my CBA-III to discharge each battery using a constant 30 amp load:
I charged the pack back up using my Zivan NG5:
Here’s the first time I charged the pack last year for comparison:
I found out a few things that I want to remember for next time. First, the CBA-III shut down due to overheating several times (which is why I don’t have numbers for the first 10 batteries on the plot). I solved this issue by pointing a powerful fan at the CBA-III and that took care of the issue.
Another point is that I use really long leads to discharge the batteries. Last time, I had found that the CBA-III was measuring about 2 volts when the battery was down to about 2.5 volts. This time, I found I had to go down to 1.5 volts. I must have messed up last time and not really taken as many amp hours out of the batteries as I meant to. The voltages shown in the plots are as measured by the CBA-III. I did not actually take my batteries down to 1.5 volts!
The batteries had between 1300 and 2200 minutes of run time remaining. This translates to between 10 and 18 amp hours. I take this to mean that I didn’t quite hit the bottom last time I balanced. Also the LinkPro might be reading a little more consumption than actually occurred.
There’s one battery in particular (#41) that didn’t fall in the same range as the others. I’m not sure if it’s failing or if it was just that far out of balance with the others. It definitely needs more investigation.
The charger seems to be working great. If I integrate the amps delivered into the pack over time, I end up with about 175 amp hours. The charger is supposed to be set up to be conservative, with a cutoff voltage of just over 180 (about 3.6 V per cell).