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Luna Battery LVC cuttoff to high

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    Luna Battery LVC cuttoff to high

    I have a 14S2P luna battery. It uses Samsung 30Qs The Low voltage cutout on the BMS kicks in at 46.5V which is to high and limits the bike range. The battery has only about 20 charge cycles on it and is only charged to 56.8V, the controller current limits at 12 Amps and it monitored with a CA. Originally the LVC was about 42V I think. I assume there is a fault in the BMS does anyone no which components set the LVC voltage or have a circuit diagram?

    #2
    From my notes these are typical rates:
    100% charged: 58.8v
    50%: 50v
    20%: 45.9v

    I don't think it's unreasonable for the BMS to kick in at 46.5v. That's perhaps 25% charge and you'll have very little range at that point. It's recommended not to run below 20%.
    I've never seen mine reach 42v.
    But others may have had different results.

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      #3
      The Samsung spec is for LVC at 3V a cell or 42V for 14S. Cutting out at 46.5V shows only 2.85 AmpHrs has been used Clearly something is wrong with the BMS. Also powering off which rebounds the Battery voltage to 49V does not bring the BMS back to life, only applying the charger for a few seconds will allow the BMS to output again.

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        #4
        Resting voltage of 46.5 is so low that a quick blip of the throttle makes it sag to 41 on a 2p battery. It is the sag that is tripping the bms. You can PAS for miles if you are careful, but one moment of exuberance and your just P the rest of the way home. Paxtana's little gizmo with a 9 volt would come in handy here, but I don't have one.

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          #5
          No the rest voltage is 49V. Even slowly pulling the voltage down with a variable load trips it. There is no spike.

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            #6
            You're a 90% charger, so give it an extended full charge and let it balance. The BMS will trip when any of the 14 series groups is too low. Perhaps one of the 14 groups got unbalanced, say it's .2-.3 volt lower than the rest. Easier for this to happen with a smaller battery.

            Fourteen little comparator IC's are monitoring your cells on that BMS. You need the eyes of an eagle, the hands of a microsurgeon or access to a surface mount repair station to change anything on those little cards.


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              #7
              Thanks, makes sense I will charge it to 4.2V per cell (58.8V total and leave it to balance overnight then try again.

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