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24v 20Ah DIY battery pack

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    24v 20Ah DIY battery pack

    Hello guys...!
    I did my 24v 20Ah battery pack from the old laptop batteries. individual battery with the rating of 2200mah nearby. I tested out all batteries with discharger and finally make the arrangement with parallel and series.
    I connected the battery pack with 7S 24v BMS. I have faced the issue of BMS cut off charging without fully charge my battery pack. I inspect each series they show the result of the different voltage range.
    My question is BMS is used to charge the series with balance method. But my BMS does not work it out. Please guide me on this issue.

    #2
    Im no expert. but u might have a bad cell. I wo
    uld open up the pack and check each series and each cell. if your voltage is not that off, wire it for a balance charger so u can see whats going on when u charge it.
    Last edited by D.808; 11-07-2018, 10:37 PM.

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      #3
      I agree, possible bad cell. If you haven't fully checked and matched each battery in the pack then it is unlikely that a BMS will be able to handle all the different voltages in the pack. Used batteries would very likely have dead or very worn cells.
      I would take the pack apart and charge each cell individually to 4.2 volts then reassemble it to see if the BMS can handle that. It would be best to get a quality 18650 charger that can discharge and measure the true capacity of each cell and rate the internal resistance of them. Then put the packs together using cells that tested to be similar.

      Also be aware of what these batteries can do if mistreated.....Google "Lipo fire"

      Use proper Lipo chargers, never leave them unattended while charging, have a fire extinguisher....

      What can happen in a pack with a bad cell is that the good ones will try to charge the bad ones, and while a charger can provide reduced amps a battery will give it all, and exceed both its output and the input on the bad cell, causing them to heat up. Never connect cells or packs together if there is a voltage difference between them.
      The same thing can happen in use, even if they all started out at the same voltage. The high capacity low internal resistance batteries will charge up the weaker cells that go dead first.....

      This is why premade packs like the LUNA ones are a good buy. Luna uses a fuse wire on each cell in their newer packs, this disconnects a cell that goes bad and saves the rest of the pack.

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