7P20S- 3 cells not charging to max

Batteries, Chargers, and Battery Management Systems.
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windchaser   1 mW

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7P20S- 3 cells not charging to max

Post by windchaser » Feb 12 2018 2:05pm


I have a 7P20S battery with 140 cells and 3 of 20 of the series are not charging fully- it is about 9 months old and only done say 30 cycles. I am using a Adaptto Max-E Controller and BMS.

17 the cells are very close to 4.16V. I have 3 that are low, 3.53, 3.7 and 3.8. these are on 3 different bms boards- all in position 2.

This severely limits the range of the bike since the BMS starts shutting down when the the lowest cell hits minimum- usually when the pack is showing over 80%:-((

I can't really believe I have bad cells in this pack already. Anyone have any ideas what i can try to re-balance this pack?

thanks in advance.


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dogman dan   100 GW

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Re: 7P20S- 3 cells not charging to max

Post by dogman dan » Feb 13 2018 8:17am

At 4.16v, you don't have any bad cells in the battery. 3 of your groups are only showing the normal wear early, at worst.

They might just be out of balance too, so try balancing more, manually, or just the ride around the block and charge again method. Charge full, wait 30 min, then try to recharge again. If the charger wont start, ride around the block, not even close to a mile, then recharge. This will repeat the charger/bms balancing cycle.

Eventually, normal for all your cells will be 4.15v or so. But right now I think it's just out of balance.

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amberwolf   100 GW

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Re: 7P20S- 3 cells not charging to max

Post by amberwolf » Feb 13 2018 1:50pm

If the BMSes have a balance function, then each group 2's balancer may be stuck partly on, continously draining those cells at a low rate.

Or, the BMSes are powered by only the group 2 cells (which would be odd), and have a high power usage (also odd), causing those groups to drain constantly.

I'ts also possible that you happen to have 3 groups of bad cells, all in the same position in the pack, but it's much more likely there is a design or manufacture problem with the BMSes.

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flippy   10 kW

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Re: 7P20S- 3 cells not charging to max

Post by flippy » Feb 14 2018 3:30am

manually charge the low cells up to 4.2 and match them with the rest. charge slowly (under 1A) directly tru the balance wires.
Lithium beats liquid dinosaurs.

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