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Motor Damaging Battery

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    Motor Damaging Battery

    I have a BBS02 and I have two newish batteries that are having issues. The motor cuts out at 50V on both batteries. The same thing happens on a second bike/motor with these batteries. My theory is that the motor is causing damage to the BMS of the battery.

    1) Could the motor (short, controller issue, etc) cause the battery BMS to be damaged?
    2) Why would the motor cut off at 50V on these 48V batteries? Voltage surge due to BMS issue?
    3) Is there any info on how to replace a BMS (what model, where to purchase, and how to install?


    Been following your several posts on this frustrating problem. May I get the particulars of your system? Battery make and model, BMS Make and model, Display, motor age and past issues with.
    What are the amp draw readings before the motor quits? Are you losing power to your display?
    See my completed Magic Pie V5 rear hub motor E-Bike build HERE.


      On the bike with suspected issues, I have a eRAD BBS02. I will be replacing this controller with a Luna controller. On the bike that has never had issues, I have the Luna BBS02.

      I bought the batteries from China. One has generic cells, and the second battery had Panasonic cells. They were purchased from different sellers. I have a buddy that bought a similar battery that did not have any issues.

      I purchased a comparable 13S BMS via Amazon and made sure it had the same connectors. We did a good job with the solders for the three main wires (B, P, C).

      The voltage shows 50.5V on my 48V battery. When going up a hill, it drops to 48.5V and then the motor cuts off (no power to display either). In order to power up the bike again, I have to unplug the battery from the motor for 10 seconds and then plug it back in and power up the bike (otherwise, bike will not turn on). The bike then goes a little further and shuts back down. If I go back to flat ground, it lasts a little while longer but then starts cutting off with even a slight hill. I have the same exact symptoms on a second motor I'm testing with.

      If I monitor the Watts used, the battery cuts off at 500W at first and then even at 300W. I tested all the cell groups via the BMS harness, and they all read 3.83V (exactly the same for each set), with the total at 48V (the math did not quite add up).


        Did you try riding the bike with power directly from the cells (bypass the bms) ?


          Is that experiment worth the try, re-soldering the connections? Is there another way to load test without using the bike and bypassing the bms without re-soldering?

          If cells go bad, wouldn't you see the voltage drop to ~42V before the motor dies? Why would the motor die at 48.5V on two different bikes? Massive voltage drop under load that I'm just not seeing on the display?


            Atleast my custom battery had a problem with mixed cells the BMS didn't supply power sometimes, the voltage was showing normal too, like 50V.


            • danbaron
              danbaron commented
              Editing a comment
              What did you do... just buy a new battery, or was there a solution?

            • brone
              brone commented
              Editing a comment
              I just made a on/off switch to turn on BMS bypass when the battery stopped working. So far it has done me well. Can't tell if it'll work for you. It could be anything - the controller, battery, bad wiring

            To clarify... everything runs perfectly UNTIL voltage level approaches 50 vdc?

            Do you have a programming cable?

            Originally posted by danbaron View Post
            On the bike with suspected issues, I have a eRAD BBS02.

            750 watt model?

            I have the Luna BBS02.

            Is this the #2 test motor?

            ... and the second battery had Panasonic cells.

            What type of cell? Link to battery page?

            I purchased a comparable 13S BMS via Amazon and made sure it had the same connectors.

            Make and model of old one? Link to new Amazon BMS?

            The voltage shows 50.5V on my 48V battery.

            As shown on your display?

            I tested all the cell groups via the BMS harness, and they all read 3.83V (exactly the same for each set), with the total at 48V (the math did not quite add up).
            At this time I see the last line as the most interesting... A 30 percent discharged battery with perfectly balanced cell groups. And as you say, the math does not add up.

            Please review this knowledge thread on BMS's. HERE.
            And double check your installation. If all is well would you please provide the following readings...

            Main B- to B1+ =
            Main B- to B2+ =
            Main B- to B3+ =
            ECT... to B13 thru all 13 groups.

            Main B- to Main B+ =
            CH- to CH+ =
            Battery Connector - to + =

            Now that your warmed up... repeat with the battery under load for at least the cell groups. I like to use a resistance heater of some sort wired to the battery output. Say about 200-500 watts if possible.

            This may seem like a bit. But if you could provide the other information requested, perhaps it could be avoided...but the more data the better! :-) Use all electrical safety precautions and practices..

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


              I am not able to test the harness wires while the harness is connected to the BMS. I have to disconnect the harness to test. There are no access points with the harness when connected.

              Correct, everything is fine until I hit about 50V and with higher wattage (from a hill) that drops the battery to 48.5V... basically it's cutting out at 48.5V.

              I'll have to track down the model details on the BMS. I ordered a while ago and the label is now missing from taping it onto the battery. It's a 13V 40A with the correct harness and wiring.

              At the time I tested, I was reading 48V on the motor port, the charging port, and the groups of cells. Everything tested out well. I had an engineer helping me at the time.

              Are you still suspecting it's a bad BMS? If the battery cells were bad, wouldn't they quickly drop well below 48V?

              Do you have a particular item link I could use to purchase the heater / load testing unit... I'm not quite clear what to purchase. I understand I'll need to resolder the connector to fit on my battery.


              • Tommycat
                Tommycat commented
                Editing a comment
                With the information I have right now I'm suspicious of a weak, undercharged or damaged cell or connection. That is tripping the BMS under load and sagging a group. Being newish batteries, you have started out with several 100% balance charges? Leaving the charger on overnight? Will it hold at 54.6 vdc? Due to the series and parallel configurations it can hide behind a normal voltage reading, as Brone has mentioned. My load is just an old blow hair dryer (120vac), plugged into an extension cord. That I replaced the plug on with an XT60 connector that mates with my battery discharge connector. I've seen others use old toaster ovens. All very low tech. Looking forward to your BMS's and battery specs. And the answers to several other questions.

              After replacing the BMS one more time and still having no success, I finally discovered that there are 8 cells (in a series) that have no voltage reading. Is that unusual? Should I simply purchase 8 replacement cells and weld them back in place?

              I would purchase these cells:

              And this welder:
              Attached Files


                I would verify the battery wiring, but yeah, it would be bad if you have a bunch of cells with no voltage reading.

                Your 13S battery should have something like 54.6 V fully charged and maybe 41 V discharged (depending on what it is set to discharge to). Something is not right if you aren't at those voltages. It could be bad or heavily unbalanced cells.

                My case the cheap battery had severed 2 BMS voltage monitor wires when they installed the cells into the battery case. Over time, the battery became heavily unbalanced and started dropping out just as you say, it would run for a bit and cut out very early. I manually charged all the cell groups to the same voltage and installed a new BMS and everything has been fine since.

                Can you manually charge the dead cell group to get it back in range the BMS can handle?


                  8 of the batteries register no voltage at all (0). How would I charge just these cells? Cut them out of the grid, and charge them manually? I'm assuming it's best to replace them ($50). I've replaced the BMS as well. Anything else to consider?


                  • JPLabs
                    JPLabs commented
                    Editing a comment
                    If the cells are at zero volts, they are destroyed! Please don't charge them. This is a fire risk, even if you get away with it, at first. Very bad idea.

                    This is the first rule of charging Lithium batteries - more or less....don't recharge severely over-discharged cells.

                  I have purchased new cells:

                  I will replace the cells, and use a spot welder to connect them with nickel strips.

                  I hope all goes well.
                  Last edited by danbaron; 08-27-2018, 12:01 PM.


                    Me too, good luck with it. nice job diagnosing it.
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