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Battery Capacity Question

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    Battery Capacity Question

    Hi Everyone.

    Long time lurker, first time with a serious post.

    I've had an em3ev BBSHD setup for about 4 months and until today it's been working perfectly.

    Today on my way home my battery died and now that I've charged it I'm not sure what I'm looking at in the BMS, but to me it appears the battery is only holding 50% charge.
    I've attached images of the BMS app screenshots. One shows the summary, the other the individual cell values.

    I've only had the battery in use for 4 months and only get the opportunity to commute on the bike twice a week due to school runs, so have only used the battery for approx 32 days since owning it.
    After each days use (64km total riding) I give it a slow charge which takes 3 or 4 hours to complete and if I know I'm not using the bike for a while I leave it discharge and charge the night before I'm going to be using it again.

    This is the first time I've looked at the BMS info, but to me it appears that the full capacity is 14750mAh, but a full charge is now only showing as 7311mAh capacity.

    Is anyone able to confirm my suspicions?

    Is there anything I can do to reset the capacity and get the full 14750mAh back? (discharge, reset BMS etc).

    Many thanks for looking.


    I'd contact EM3EV if you haven't already, and send them those screenshots. While waiting for them to reply, have a look at, which may hint on potential problem areas.

    I'd hope for a bad BMS balance sense connection. Is your battery a 52 volt jumbo shark? Does it get warm while charging?

    One of the gotchas with these batteries is the amount of cells that need to be put in series to reach the desired voltage. Like a string of old Christmas lights, one bad cell will affect out the whole string. A jumbo shark has 5 in-parallel strings of 14 in-series batteries.
    Last edited by ncrkd; 03-19-2019, 07:12 AM.
    2nd build, 2018 Crust Scapegoat, BBS02 or BBSHD, Rohloff IGH
    3rd build, 2018 Crust Evasion step-thru, BBS02, Shimano Nexus INTER-3 IGH
    4th build, 2016 Salsa Marrakesh flatbar frameset, BBSHD, Alfine 8 IGH

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      Yes, I have contacted em3ev, but it's always nice to get a second opinion and it gives me something to read while waiting for them to reply.
      Yes, it's a 52V Jumbo Shark (30Q).



        Yeah, that badly out of balance cell group is going to drag the capacity down. Looks like the BMS is suppose to balance any where above 50%. But with that one lagging so far behind doesn't have much of a chance to catch up. While waiting for a responce I'd try several 100% charges allowing it so sit an hour or two between restarts (ride for a few minuets if needed) to see if it would come up. Mainly just wanted to say what a neat window to the batteries operation that blue tooth BMS is! Hopefully if it does recover, you can keep a closer eye on it. Perhaps just needing to change your charging habits.
        Last edited by Tommycat; 03-20-2019, 08:50 AM.
        See my completed Magic Pie V5 rear hub motor E-Bike build HERE.


          Originally posted by Tommycat View Post
          Perhaps just needing to change your charging habits.
          What do you recommend?
          I thought I was doing the right thing by not fully discharging during use, not leaving them sat fully charged for long periods of time between use and only ever charging to 90% unless in a rush.


          • Tommycat
            Tommycat commented
            Editing a comment
            With your type of BMS which is suppose to balance charge above 50% that all sounds perfect. Just trying to leave a glimmer of hope open as it sounds like the BMS is not charging properly or you have a weak cell group. :-( Did you fully balance the battery when you first got it? What do you concider full discharge? Only other thing I can think of is if the BMS configuration settings are incorrect. Got a screen shot of the settings tab?

          Hi Tommycat,

          Apologies for the delay, work and holidays have got in the way the last few weeks.

          Yes, the battery was fully charged when I first received it to the 100% setting of the charger. With regards to a full discharge, my understanding (as the DPC-14 cannot display the % correctly) is that 44V should be the lowest I can go before the battery is considered empty, but I also thought that this is bad practice and charging to 90% and discharging to 10% was the best way to prolong the life of the battery pack. I'm lucky to get below 50V now before it turns off and displays a flat battery. With regards to a weak cell group, this was the initial indication, but on charging the battery to 100% today and checking the BMS again it appears I now have 3 or 4 cell groups showing as low compared to the rest. I've attached a screenshot of the cell groups and BMS settings if you're able to provide any direction.

          I do wonder about the battery design voltage of 36000mv in the BMS config (36V) as this is a 52V pack. Shouldn't that be 52000mv?

          Many thanks.


            Welcome back. The first thing that hit me... is your charger outputting 58.8 vdc at 100% charge??? And is it's current shut-off point low enough? Great info here...



            The closer you can stay to the nominal battery charge the better... But most people have to charge to 100% occasionally to balance the cells.

            LOTS to unpack with all those settings! Since the low voltage cells cover more that one MCU, hopefully it's just a setting or two and not electronic.

            "I do wonder about the battery design voltage of 36000mv in the BMS config (36V) as this is a 52V pack. Shouldn't that be 52000mv?"
            I was leaning your way, but could "design voltage" also mean the cells (30Q) nominal voltage? Which would be 3600 mv...

            What is the BMS's make and model, P/N, ECT...? Got to find a manual! ;-)

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


              The charger is Em3ev's 5A/300W charger. It states 58.8V on the unit, but whether it is outputting this I don't know without measuring.

              The BMS is also from Em3ev, but when they couldn't supply IOS software I asked for the make and model to try and find alternative software myself, but they wouldn't tell me.
              I have now had the battery case open, but there doesn't appear to be any markings on the BMS to indicate what make or model it is - it's just a small silver unit with a connector at one end.
              It looks identical to that on their website -