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    18650 battery pack help

    Its my first post.i am not building an e-bike but i have some time spend understanding 18650 batteries.i tried to build my first battery pack 12v 10ah (3s-4p) but i am having some issues i did not thought before starting this pack. I needed this pack to power different devices which work at 12v 8,4 and 5v so i thought it would be better to use a voltage regulator instead of a pcb.After using my turnigy accucell 6 to balance charge the battery i am noticing deviations in the battery cells voltage. So i get values like 4,15 4,18, 4,19 .i thought balance charging the pack would not give values more than 0,01 deviation.if there is any suggestion how to find the best solution for me so the pack is balanced i would appreciate it. After having fully charged the pack i powered 2 devices to check how many amps will be consumed and what time will do so the regulator will cut off giving power. But it did not stopped.i had to unplug after 8 hours and checked the voltage of the cells which where giving 3,78 3,60 2,70 .That made things for me more complicated .i also have the feeling that my turnigy accucell do not work properly.Its supposed it can charge up to 6amps but when i do it gives an error about input voltage .i noticed that the input power works at 1,5 amps so that is my maximum amp i can charge.if i go above turnigy stops giving error.i am not sure if i use the original power cord or i confused it and using from another device .I am describing how my situation is now.so feel free to give any suggestions they can help me out thanks.

    #2
    Your cells should balance closer than that, if given enough time, yes.

    Regardless, you had them close before your discharge test. But after, they were way off! That tells us the parallel groups have different capacities. They are not matched.

    Your pack can never work optimally if the parallel groups don't all match, no matter how carefully you balance them. you will only get the performance of the weakest group. And without BMS, running one group dangerously low is very easy to do. I'm afraid you build a bad pack. Or damaged some of the cells.

    Sorry.

    You built it with used cells, I bet?
    Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

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      #3
      If you can get a multimeter and check would be better. If its one volt difference something is wrong. As for the low voltage error is that when balance charging? I had same error when balance charging. Solution for me is to charge up to 4.0v or more then switch over to balance charge them.

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