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    Bad battery?

    Bike runs for about 5 minutes on a level street and drops dead. 36 volt battery. I set up a makeshift load out of 3 1156 light bulbs in series, about 2 amps a piece figuring 6 amp draw.. Then connected the battery and monitored the voltage drop with my meter. Worked for an hour and a half slowly lowering the voltage. Went back out 10 minutes later and the lights weren't lit, voltage on the battery was at zero. My assumption is the battery or its protection circuit is failing and not the bike controller or motor. Any suggestions?

    #2
    Hi TryDave,
    And welcome to the forum!

    How low where you able to monitor the voltage too? (best guess at voltage drop-out) Are you comfortable opening up a battery pack? How old is the battery? What type, (Li-Ion) and amp/hour rating?
    See my completed Magic Pie V5 rear hub motor E-Bike build HERE.

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      #3
      Originally posted by Tommycat View Post
      Hi TryDave,
      And welcome to the forum!

      How low where you able to monitor the voltage too? (best guess at voltage drop-out) Are you comfortable opening up a battery pack? How old is the battery? What type, (Li-Ion) and amp/hour rating?

      A friend has the bike and wanted me to find the problem as I spent my life in the electronics field. These bikes are new to me. Seem to be very complicated. The battery is a 36 volt 8 AH. The voltage dropped to 31 volts in an hour and a half. I took a ten minute break and when I came back, it was completely dead. I told the guy I may have to open it. As I understand, it's full of 3 banks of 18650's wired is a series parallel setup. I'm not too up on these batteries in a configuration like this. I measured the voltage drop with my Fluke 8750 for the entire test. Just trying to save the guy some money. He has had the bike for a little over a year. The battery is tagged at october 2017. For all I know, one 18650 could be a problem. I'm assuming it's a Li-Ion. He doesn't really go far with it other than short trips.

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        #4
        Originally posted by TryDave View Post

        ... it was completely dead.

        For all I know, one 18650 could be a problem.
        Sounds like the Battery Management System shut it down because of low voltage in one of the cells... Not knowing if your friend was properly charging it to a balanced state. I'd recommend verifying the correct charger output of 42vdc, and give it a good long series of full balancing charges. If that had been tried or you want to get right to it... it may be time to open it up and check the individual paralleled groups looking for one with a low charge.

        See my completed Magic Pie V5 rear hub motor E-Bike build HERE.

        Comment


          #5
          Originally posted by Tommycat View Post

          Sounds like the Battery Management System shut it down because of low voltage in one of the cells... Not knowing if your friend was properly charging it to a balanced state. I'd recommend verifying the correct charger output of 42vdc, and give it a good long series of full balancing charges. If that had been tried or you want to get right to it... it may be time to open it up and check the individual paralleled groups looking for one with a low charge.
          I agree. Time to cut it open. Thanx for all the help!

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