Faulty BMS?

  • Hi guys,

    Just joined the forum! I think I have a faulty BMS that is causing my Onewheel to either think it's at 0% battery or overcharged even though the battery is fine.

    I downloaded the older version of the Onewheel app to check what the Onewheel thinks the battery cell voltages are:
    alt text

    As you can see, the app is reporting that all my cells are at 3.32V except the last two which are at 2.74V and 3.90V. Thinking that I had a broken battery, I contacted Onewheel Support but they never responded to my multiple calls or emails :( . So, I opened up the battery module and I opened up the heatshrink around the battery cells. To my surprise, I measured each battery cell to be exactly 3.32V! The battery was fine.

    Then, I also realized that the app's measurements of 2.74V and 3.90V also average to 3.32V so I'm confused. I'm not sure if my BMS is shot or my controller board's firmware has poor logic in it and is doing something funky with the last two cell measurements.

    Oddly enough, when I charge my Onewheel overnight, my battery charges to 58.2V and my app reports that all the cells are 3.63V. However the misreading of the cell voltages appears after I ride my Onewheel for about a mile or so.

    Any thoughts?

  • @Carbon Did you measured the voltage of each cell using the balance connector or on the cell itself ? because if you measure it on the cell itself I'm afraid you could measure only the average of the cell's voltage which are in parallel.

  • @Carbon

    If you search on here or Facebook you'll see a history of issues like this. Typically the FM recommendation, which worked for me in the past, is to run the board down to 1% battery and let it charge for 48-72 hours. This will allow the BMS to balance the voltages for each cell.

    I had to do this a few times on the OW+ and it correct the issue. If you look in the manual it will actually recommend doing this.

  • @Tartopom I measured both the balance connector and the cells themselves.

    I don't think I would have an issue measuring the cell's voltages since they are in series? There are 16 cells with a nominal voltage of 3.7V each so the total battery voltage should be around 59V which is what I'm seeing.

    If they were in parallel, the total battery voltage would be lower and all the cells that are in parallel would be the same voltage since the "higher" voltage cell would just discharge into the "lower" voltage cell until they're equal.

  • @skyman88

    I tried doing that recalibration procedure several times but unfortunately I haven't seen any good results :(

  • @Carbon

    So when my app and board refused to be in sync on battery life, I did the above procedure with 48 hour charges, 3 consecutive times and it finally broke the cycle and got my cells balanced.

    Sorry to hear yours isn't correcting itself.

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