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    bms/battery issue balancing

    Hi

    I have 52v shark battery. The case broke and it got wet inside and then the bike would shut down after a few minutes of load. I took it all apart and found 2 blocks of 5 cells that were showing 3volts the others all showed 4.3 or 4.4
    So I have changed the cells but when I charge it up the new blocks don’t get charged up which I assume is correct since 12 cells at 4.4 is already getting me close to the 58v cut off

    Because of this when I put load on the bike shuts down after a minute or two.

    I am guessing this means the bms can’t balance such a big difference in voltage between the blocks- does that make sense

    If so I am planning on bypassing the bms to be able to run the other cells down and hopefully then when the bms is reattached it will be able to balance them as they should be closer together. Does that make sense or should abms be able to balance it anayway and it just needs a new bms?

    Thanks for any help

    #2
    When I repaired my battery with a failed BMS I individually charged the cell groups to be within about 1/10 of a volt of one another using an RC car Li-Ion charger using alligator clip leads. You have to be very careful not to short the battery doing this. When I put on the new BMS it was able to handle the difference and balance the cells (presumably, as it still works).

    Also realize that cell balancing can be a very slow process when they use low power handling resistors to bleed off the power, and it might only do it on the charger. Might have to leave it hooked up for days or weeks to balance such out of balance cells.
    Last edited by Viking79; 08-16-2018, 07:31 AM.

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      #3
      Originally posted by Monti View Post
      Hi
      the others all showed 4.3 or 4.4
      It's a VERY bad news cuz Lithium doesn't like overcharging at all. Discharge them manually as soon as possible. Manually bring all the parallel groups to ~4.0V with as low difference as possible and connect the BMS. Charge them and measure the voltage on all groups after 1hr after charging is finished and the charger is unplugged. Then make a couple of full discharge-charge cycles with measuring and registering voltage after 1hr every time. If your groups keep going balanced after that, then it's ok, if not - your cells were overcharged and need to be replaced.

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        #4
        Some lithium cells charge to 4.4 V, but need to know the chemistry.

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          #5
          I don't think Monti's cells are 4.4V ones

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