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unbalanced lipo pack

unbalanced lipo pack

Old 12-18-2009, 04:26 PM
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Hi, I bought two lipo packs (2s 7.4V) at the time. Both work well, but one of them seems to have unbalanced volt issue. The first few times I spotted one cell always had a little low volt than the other cell but not much, probably 0.01, both cells can go back up the same volt after balance charge. But after about 10 charges, the volt difference became 0.3~0.4, and I can notice the car lose punch very quick because one cell was drained quicker than the other. The balance charge can't help because my charger stops charging when it detects one cell is full. I guess it tried to balance two cells but the difference was huge so it gave up. Can anybody help? Is it because I was unlucky to buy a defective pack (other one doesn't have this issue)? Is there anything I can do to make this pack alive?
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Old 12-18-2009, 04:39 PM
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If you can make it up to the track tomorrow, I'll try to help you out. If not, let me know when you can get there and we'll work it out.
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Old 12-18-2009, 07:11 PM
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I suggest if you can get assistance from others to help you balance it up.

Just becareful if your ESC cut off at 6V. Uneven cells will cut off lower voltage hence damaging the LiPo pack.
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Old 12-18-2009, 08:28 PM
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my other lipo packs have never experienced this problem, their volt difference is always small (within 0.005~0.008), but this one has 0.4v difference, one cell has 4v and the other has 3.6 after 5 min run. It seems one cell drained out the energy faster than the other. I don't know if balance them up will help. Oh by the way, I always balance charge, but this pack seems to have bigger volt difference time after time, and now the difference is so big that my charger will not charge the cell with lower volt up to the other cell
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Old 12-20-2009, 07:20 PM
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Ok, what you can do is which cell has the difference. Charge the cell individually. connect the +ve to balancer port and then -ve to balancer port. Charge them individually till full. After full charge you get same readings. Try run for 5 mins to see the differences.
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Old 12-20-2009, 07:32 PM
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Thanks buddy, I will try. Here is another question, what will cause two balanced cells having hug volt difference after the ESC cut-off kicks in? Could ESC cause this problem? Or a damaged cell?
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Old 12-20-2009, 07:59 PM
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I do not run the car till ESC cuts off 6V. When you notice slower performance or lack punch. Just stop the car immediately.

Hence I believe your prob cause by one of the cell goes below safety threshold voltage.
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