sviatpizdat
10 mW
- Joined
- Aug 19, 2020
- Messages
- 27
Hi everyone!
I have a battery 16s5p of Samsung 30q.
After half a year of occasional usage (about 20-25 full cycles) I found that, when the pack is fully charged, the 11th parallel is 0.25V lower than the highest one. When balancing turn-on, it balances to 0.2V (at about 4.1V of the highest cell) but then balance only gets worse! To about 0.3V (at about 3.9V of the highest cell). I've repeated a few attempts to balance it, but the picture did not change!
I also found, that when the balance is on, the 11th loses voltage (but it is the lowest cell, and should stay as is). When the balance is off it sometimes loses voltage, sometimes stays as is (but I had only few observations, so not sure about self-disharge).
My BMS has passive balancer. When cell is loaded by balancer, the (B) sign is shown near the cell in the BMS's mobile app.
When discharging, the 11th parallel seems to discharge slightly faster than other ones, but that's probably explainable by an initially lower voltage. If it'll have less capacity, I guess it would also charge faster then the others.
I've disassembled the battery and un-soldered the 11th from the (-) side, so I can measure individual cells, while (+) is still connected.
By discharging in the range 3.42-2.8 the capacity of individual cells is 0.407-0.416Ah, and resistance is 12.84-13.17 mOhm. The resistance of cells in nearby totally healthy parallel is also +-13mOhm.
The measurements seem totally fine, so I guess it may be a BMS balancer problem.
The BMS is this one https://www.lithiumbatterypcb.com/product/16s-17s-18s-19s-20s-lithium-or-lifepo4-smart-bluetooth-battery-bms-with-50a-constant-current/
It seems to be connected properly.
Where do you think the problem may be and how to resolve it?
I have a battery 16s5p of Samsung 30q.
After half a year of occasional usage (about 20-25 full cycles) I found that, when the pack is fully charged, the 11th parallel is 0.25V lower than the highest one. When balancing turn-on, it balances to 0.2V (at about 4.1V of the highest cell) but then balance only gets worse! To about 0.3V (at about 3.9V of the highest cell). I've repeated a few attempts to balance it, but the picture did not change!
I also found, that when the balance is on, the 11th loses voltage (but it is the lowest cell, and should stay as is). When the balance is off it sometimes loses voltage, sometimes stays as is (but I had only few observations, so not sure about self-disharge).
My BMS has passive balancer. When cell is loaded by balancer, the (B) sign is shown near the cell in the BMS's mobile app.
When discharging, the 11th parallel seems to discharge slightly faster than other ones, but that's probably explainable by an initially lower voltage. If it'll have less capacity, I guess it would also charge faster then the others.
I've disassembled the battery and un-soldered the 11th from the (-) side, so I can measure individual cells, while (+) is still connected.
By discharging in the range 3.42-2.8 the capacity of individual cells is 0.407-0.416Ah, and resistance is 12.84-13.17 mOhm. The resistance of cells in nearby totally healthy parallel is also +-13mOhm.
The measurements seem totally fine, so I guess it may be a BMS balancer problem.
The BMS is this one https://www.lithiumbatterypcb.com/product/16s-17s-18s-19s-20s-lithium-or-lifepo4-smart-bluetooth-battery-bms-with-50a-constant-current/
It seems to be connected properly.
Where do you think the problem may be and how to resolve it?