velowatt
1 W
- Joined
- Apr 6, 2009
- Messages
- 60
I built a 12s Headway pack (10Ah cells) for nominal 36V run through a older-style "Signalab" 12- channel BMS board (same as on the V1 Ping packs). After taking the pack out for a longish ride, I got a bit over 5Ah before the voltage (total pack) sagged to 32V, which seems low. I went to charge the pack up, and noted that the BMS board was slightly warm to the touch, but I have to climb a steep hill to my house, so I figured that maximum current draw had just happened. I took a look at the board and was surprised to find evidence of Black Smoke (soot on the protective foam loosely associated with the BMS board)! A picture:
Close up of 'burned FET:View attachment Soot.JPG
Now the pack does not want to charge. Looks like an FET in the corner may have blown, the soot is collected around the B- solder terminal on the board. The FEt package looks intact. Other tracings and components appear OK, no burned spots or shorts.
View attachment Burned!.JPG
I disconnected the battery and tried to charge directly across the + and - terminals. After a bit over an hour, the charger shut off as usual. Pack voltage off he charger was only 33.4V! (Usually settles in at about 40.4 after charging and stays there). I measured the voltage across each cell and got this (starting from positive terminal of the string)
Cell 1: 3.32
Cell 2: 0.82
Cell 3: 3.32
Cell 4: 3.32
Cell 5: 0.32
Cell 6: 3.64
Cell 7: 3.23
Cell 8: 3.76
Cell 9: 3.32
Cell 10: 0.01
Cell 11: 3.75
Cell12: 0.63
I think cell 2, 5, 10, and 11 are toast (as is BMS). The others are probably salvagable. What do forum members think? I would like to replace the BMS with one that actually works (LVC for each cell would be most important to me, since I hate trashing brand- new good cells). I also would like to not spend an excessive amount of $$, since this pack is an 'extra' pack that can be used for increased range or better performance on a couple of different bikes (I don't deend on it for commuting).
The bike I was using this pack in runs an older brushed WE motor, controller is a '35A' unit that can draw MAX or 33 amps. Max power draw from this battery is just about 1000W for a short time. The ride which 'kiiled' the BMS was 20 miles. used 5.15 Ah, and about 9.5 Wh/mile (I went slow with lots of pedaling to maximize range and get a workout- usually draw 12-20 Wh/mile depending on hills and speed).
My questions to the Form are these
-Can I assume the 8 cells tthat are still above 3V are OK?
-Suggestions for a reliable/basic BMS that won't break the bank
-How low should low voltage cutoff take Headway cells? Is 2.5V per cell about right or is that too small a safety margin?
Thanks
Close up of 'burned FET:View attachment Soot.JPG
Now the pack does not want to charge. Looks like an FET in the corner may have blown, the soot is collected around the B- solder terminal on the board. The FEt package looks intact. Other tracings and components appear OK, no burned spots or shorts.
View attachment Burned!.JPG
I disconnected the battery and tried to charge directly across the + and - terminals. After a bit over an hour, the charger shut off as usual. Pack voltage off he charger was only 33.4V! (Usually settles in at about 40.4 after charging and stays there). I measured the voltage across each cell and got this (starting from positive terminal of the string)
Cell 1: 3.32
Cell 2: 0.82
Cell 3: 3.32
Cell 4: 3.32
Cell 5: 0.32
Cell 6: 3.64
Cell 7: 3.23
Cell 8: 3.76
Cell 9: 3.32
Cell 10: 0.01
Cell 11: 3.75
Cell12: 0.63
I think cell 2, 5, 10, and 11 are toast (as is BMS). The others are probably salvagable. What do forum members think? I would like to replace the BMS with one that actually works (LVC for each cell would be most important to me, since I hate trashing brand- new good cells). I also would like to not spend an excessive amount of $$, since this pack is an 'extra' pack that can be used for increased range or better performance on a couple of different bikes (I don't deend on it for commuting).
The bike I was using this pack in runs an older brushed WE motor, controller is a '35A' unit that can draw MAX or 33 amps. Max power draw from this battery is just about 1000W for a short time. The ride which 'kiiled' the BMS was 20 miles. used 5.15 Ah, and about 9.5 Wh/mile (I went slow with lots of pedaling to maximize range and get a workout- usually draw 12-20 Wh/mile depending on hills and speed).
My questions to the Form are these
-Can I assume the 8 cells tthat are still above 3V are OK?
-Suggestions for a reliable/basic BMS that won't break the bank
-How low should low voltage cutoff take Headway cells? Is 2.5V per cell about right or is that too small a safety margin?
Thanks