rush
New Member
- Joined
- Apr 28, 2021
- Messages
- 3
I recently built a 100-Ah 4S battery using batteries from batteryhookup.com. The BMS is a Daly 100-A unit (J05A-CG30, specifically marked LiFePO4 on the product listing and the case) from Amazon. It is marked 100 A/50 A charging on the case. It doesn't support bluetooth (d'oh!) or low-temp disconnect so I have ordered an Overkill Solar 120-A BMS, but I expect that it will take several weeks to arrive.
I top balanced the batteries and discharged them to about 30% capacity to get an initial functional test. Next I charged them at a 0.15-0.2C rate until the BMS cut off charging. The battery took 76.5 Ah and 1038 Wh. So far, so good.
As soon as charging completed, I tested the cell voltages. I measured the cells immediately at the end of the charging cycle and found one cell at 3.73 V. That was disconcerting. I was under the impression that an LFP BMS should disconnect charging when any cell reaches 3.65 V.
The cell voltages settled fairly quickly but they were nowhere near balanced after charging. I'm not sure what to make of that, but it's really a separate problem I think. After 90 minutes, these were the cell voltages (BMS still connected):
That's a 227-mV (huge) delta between the highest and lowest cells.
Three hours after charging ended:
That's a 49-mV difference between the highest and lowest cells.
Interestingly, that first cell was also the lowest before I did the top balancing.
In summary, I'm interested in comments on the disconnect voltage question and the cell balance after charging. I would greatly appreciate any links or references to supporting data.
Thanks.
Rus
I top balanced the batteries and discharged them to about 30% capacity to get an initial functional test. Next I charged them at a 0.15-0.2C rate until the BMS cut off charging. The battery took 76.5 Ah and 1038 Wh. So far, so good.
As soon as charging completed, I tested the cell voltages. I measured the cells immediately at the end of the charging cycle and found one cell at 3.73 V. That was disconcerting. I was under the impression that an LFP BMS should disconnect charging when any cell reaches 3.65 V.
The cell voltages settled fairly quickly but they were nowhere near balanced after charging. I'm not sure what to make of that, but it's really a separate problem I think. After 90 minutes, these were the cell voltages (BMS still connected):
Cell 1 | 3.35 V |
Cell 2 | 3.557 V |
Cell 3 | 3.553 V |
Cell 4 | 3.483 V |
Three hours after charging ended:
Cell 1 | 3.447 V |
Cell 2 | 3.496 V |
Cell 3 | 3.484 V |
Cell 4 | 3.453 V |
Interestingly, that first cell was also the lowest before I did the top balancing.
In summary, I'm interested in comments on the disconnect voltage question and the cell balance after charging. I would greatly appreciate any links or references to supporting data.
Thanks.
Rus