maarten_almighty
100 mW
- Joined
- Jan 10, 2020
- Messages
- 47
Hi,
I recently built a 20s17p battery pack for my ebike using second hand samsung ICR18650-22P Cells (2200mah capacity when new).
The issue:
Since building the battery i have cycled (discharge-recharge) it approx 5 times, up till a week ago all went well, voltages were as I would expect, when I last checked battery voltage (after having the bike stored for approx a week without using it) the voltage was approx 52Volt (when it should be approx 70v since I had charged it before storing the bike only a week prior).
I checked the group voltages, 7 out of 20 groups are 0v (or close to it... 0v-0.32v).
The groups which are 0v are B2-B4 and B12-B15 (I started counting from the negative side of the battery).
The battery:
NOTE: Prior to opening up the battery the bms's sense wires were insulated with an extra layer of insulation (duct tape) from the exposed cell ends/nickel strip for safety)
I openend up te battery pack and checked all cells/connections: All looks good (no corrosion or other damage to any cell or wire/connection).
Usage:
The batteries were only being discharged at approx 0.5C (they are rated for 10A max continuous current and I was using them at max 4A per cell during these 5 cycles). I don't live in a warm climate either so the cells definitely didn't get hotdue to my usage.
The cells did get quite cold approx 2 weeks ago (negative 10 celcius) but this shouldn't be an issue I think since from what I found only they only freeze at approx -40 degrees C (also if the low temperature was the issue I would expect all cells to have died, not just 7 groups).
My guess (what caused it):
I conclude that the issue is with the BMS since I find it highly unlikely that in so few cycles, so many cells from different parallel groups would 'die' due to the cells being in bad condition or something similar. What I think happened is that the BMS severely overdischarged the cells in these 7 groups. All wiring from the cell groups to bms is correct/intact (I have checked).
Do you agree with my conclusion? If not, what do you think is the issue that caused the 7 groups to die?
Unfortunately My BMS does not have bluetooth so I wasn't able to check its performance/the cell voltages during usage, when rebuilding/replacing the battery I will make sure to upgrade the BMS to a bluetooth capable one so I can check what it's doing..
Thank you very much!
I recently built a 20s17p battery pack for my ebike using second hand samsung ICR18650-22P Cells (2200mah capacity when new).
The issue:
Since building the battery i have cycled (discharge-recharge) it approx 5 times, up till a week ago all went well, voltages were as I would expect, when I last checked battery voltage (after having the bike stored for approx a week without using it) the voltage was approx 52Volt (when it should be approx 70v since I had charged it before storing the bike only a week prior).
I checked the group voltages, 7 out of 20 groups are 0v (or close to it... 0v-0.32v).
The groups which are 0v are B2-B4 and B12-B15 (I started counting from the negative side of the battery).
The battery:
NOTE: Prior to opening up the battery the bms's sense wires were insulated with an extra layer of insulation (duct tape) from the exposed cell ends/nickel strip for safety)
I openend up te battery pack and checked all cells/connections: All looks good (no corrosion or other damage to any cell or wire/connection).
Usage:
The batteries were only being discharged at approx 0.5C (they are rated for 10A max continuous current and I was using them at max 4A per cell during these 5 cycles). I don't live in a warm climate either so the cells definitely didn't get hotdue to my usage.
The cells did get quite cold approx 2 weeks ago (negative 10 celcius) but this shouldn't be an issue I think since from what I found only they only freeze at approx -40 degrees C (also if the low temperature was the issue I would expect all cells to have died, not just 7 groups).
My guess (what caused it):
I conclude that the issue is with the BMS since I find it highly unlikely that in so few cycles, so many cells from different parallel groups would 'die' due to the cells being in bad condition or something similar. What I think happened is that the BMS severely overdischarged the cells in these 7 groups. All wiring from the cell groups to bms is correct/intact (I have checked).
Do you agree with my conclusion? If not, what do you think is the issue that caused the 7 groups to die?
Unfortunately My BMS does not have bluetooth so I wasn't able to check its performance/the cell voltages during usage, when rebuilding/replacing the battery I will make sure to upgrade the BMS to a bluetooth capable one so I can check what it's doing..
Thank you very much!