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FAQ: Charging Batteries

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  • FAQ: Charging Batteries

    When batteries are made at the factory the cells are spot welded into parallel groups and series. A battery management System is then soldered to each parallel group.

    For example a 52 volt 11.5ah or 13.5ah Shark pack will have 56 cells and the packs is called a 14s 4p.

    When charging the Battery Management System (BMS) monitors the pack so individual cells do not go over 4.2 volt. (High voltage charger cutoff is 4.25)

    A fully charged 52 volt pack is 58.8 Volts.

    NOTE: On the BBSHD dcp-14 colour display this will only read to 56 volts. This is due to the display being configured to 48 volt. The gauge is accurate as soon as a pack drains to 56 volts.

    A fully charged 48 volt pack is 54.6 Volts
    A fully charged 36V pack is 42V
    A fully charged 72V pack is 84V

    IMPORTANT: The battery needs to be charged prior to the first ride. The packs are shipped with 30-50% state of charge only!

    It is important to fully charge the battery to 100% for the first few cycles, leave it on till the charger stops...can take up quite a few hours (depending on the capacity and charger rate) and also please charge in a safe place and no on the bike connected to the controller.

    Charging time is quite simple to estimate:

    A 13.5 ah GA shark pack will require about 5 hours at 3amps (standard basic 3a charger) about 4.5h to put pack most of the juice back (13.5ah / 3amps =4.5h) and about 30min to saturate (constant voltage mode)
    Click image for larger version  Name:	Screen Shot 2017-08-07 at 9.27.53 PM.png Views:	1 Size:	44.2 KB ID:	41846

    The battery when new can take a few cycles to balance and settle. This is called the break in period.
    Typically we recommend charging to 100% for 6 charge discharge cycles. Its also important during the break in period not to run the pack to Low Voltage Cut Off. Also take it easy on the pack by not drawing maximum amps.

    You don't need to
    discharge fully, you can only discharge the pack a few volts and then you charge it again to 100% and let it sit unplugged for a few hours. Balancing only occurs when one or more cell group reaches the 4.2V per cell mark.

    Let me explain quickly how a charger and BMS works when it gets close to 100%

    When charging as all the parallel cell groups starts to hit 4.2 volts, the charger will change setting to what is called the CV (constant voltage) then the current drop gradually down to 3-5% of the rated amperage of the charger (see graph up, CC and CV phases)

    Once at this 5-3% amp level the charger will shut down (If not do not worry the BMS as an internal protection for over charging and will cut the charge if necessary.) ONCE the first cells hit the 4.2V mark, the BMS will let the high cells bleed off to the lowest cell. Balancing can happen while charging but normally the imbalance is pretty slim and the BMS won't have the time to balance fully it before the charge done (can take a few hours to balance, it's better to let the pack unplugged in a safe place over night.)

    If you leave the charger plugged in after the charge is complete and you have a little unbalance some charger models can restart once the BMS as bleed of a little... This can cause the charger to cycle on and off depending on which model. But our recommendation is to unplug the charger once you see the green light. Leaving the charge plugged in can actually draw a little current back in the charger to power the LCD and some components.

    In the end of the break in period, you will have a balanced pack with all groups close to 4.2 volts.

    After the break in period the battery can now be charged to 80 or 90%.
    Periodically charging to 100% is required to keep the pack balanced. Charging the pack to 90% does not do this. So over time the pack can become unbalanced. So now you need to get the pack back in balance so it needs to be charged to 100% for 2 to 3 cycles in a row. The balancing process is long so when you are doing the balancing, leave the pack alone for a few hours to let the BMS do his job, you can then ride your bike and charge to 100% again...till you complete 2-3 100% charges.

    This will need to be done over a period of time. can be every 30 cycles, after a 3-6 months period and specially after a storing the battery for a few weeks (tip on storing the battery click here)

    Charging to 80-90% does increase battery life by double some say but that's only provided the packs also treated correctly.

    Other things that decrease pack life can include, running the pack under 10% of capacity. Sometimes this is unavoidable. Using a packs to the max discharge rate of the cells for long periods of time will result in poor range and permanent capacity loss over time (meaning you won't get the 400+ cycle life). The pack does shut down as it has a temperature sensor to prevent damage. These are just some examples.

    Additional Links

    How do you know that the charger is in the middle of balancing??
    This varies depending on the charger used. On some of the most common charger types that are made of plastic the only display on the charger might be a couple LEDs, often this will go from a solid color while regular charging to blinking during the balancing. On several models of the Luna charger you can tell it is balancing because the fan will kick on and off at the end of the charge cycle.
    Last edited by Sebz; 08-14-2017, 07:31 AM.

  • #2

    The LVC on the bafang is 41 volts, it will not cut off completely but you will see the power drop a lot .. LCD will stay on but show very low amperage (or watts).

    The 52V 13.5ah GA Shark pack will cut at 39.9 volts under a constant load of 6amps . At this cutoff 13.29ah were used.

    This was a test I did was on a fixed resistor started at 10amps load at 58.8V and amperage dropped gradually to 6.2amp near the 40V mark.

    45 volt under load (around 48 resting) would be approximately 15% usable capacity left.

    If you did program the BMS then it may shut down prematurely due to battery sag.
    Last edited by Sebz; 06-28-2017, 06:17 AM. Reason: clarification


    • #3
      Originally posted by Gr8fun
      In my Previous post, my main concern is that the charger does not come back on to maintain voltage as the passive cell balancing of the bms bleeds off the excess current of the higher value series batteries. Or am i being overly concerned?
      Probably being overly concerned, it will continue the balancing process as you charge it to 100% during these first few cycles. So it does not necessarily need to do all the balancing at once.


      • #4
        Hey There,

        I recently put together my build with a Magic Pie V5, and 52v 11.5ah carbon shark pack. Unfortunately, I was too giddy and excited to test my toy and I did not read up on proper first time charging.

        I actually did both thing incorrectly, by riding on the charge from the warehouse (I think it was ~53v) and ran it until voltage cut off :(

        Thankfully, I then read the forum, and have been charging to 100% and running down to about 50% and then recharging to 100%. I am on my second charge now.

        My two questions are:

        Will this be very bad for the long term reliability of the battery?
        and more importantly, is there any safety issues with what I did and the cells being unbalanced?

        I charge in an office setting at work, and am sort of paranoid of something going wrong with the battery, any advice or reassurance would be great!



        • paxtana
          paxtana commented
          Editing a comment
          it's a performance issue not reliability or safety. Did same thing with one of my first packs, identical to another pack I have except in its initial treatment. Only difference I see is mistreated pack is like 0.1v-0.2v difference after its been fully charged. So a little less capacity. The difference has mostly equalized as I continued to use the pack, it started out at like 1v difference

      • #5
        The pack seems to be working much better now. The 1 volt drop after charging dropped to about.2. I really like the batt man. Helps on efficiency and range anxiety. Consistently get 20 wh per mile at 24 mph. 15wh at 18 mph. Really sucks at 28. Well over 30 wh. Best has been 10 wh at around 11mph. All numbers approx due to hills and stop and go traffic. It is showing that this 20Ah battery is maybe between 18.5 and 19. Probably due to the cold weather. Around 40 to 45 degrees. The nice thing is that during my 15 mile commute i have power enough to get to 30 mph even after the 30 mile point if i need to. (Yellow lights). The 11.5 would start dropping out on lvc with any acceleration by then. Always had to recharge at 15 miles to enjoy ride.


        • #6
          The idea is to charge to 100% and then use the battery immediately or soon. Leaving it 100% charged for a long time on or off the charger is not good for the longevity of the battery.

          A new battery should only be charged for a first time (to 100%) soon before the first use. So build the bike then charge the battery fully before riding hard. It is likely fine to test the build gently with a half-charged new battery, but since we don't have access to the BMS leads to confirm all cells are balanced, a safer approach is to charge it to 100%, let it balance, then use it and leave it half-charged until next time you need it and charge it again.

          I don't trust cheap BMSs all that much, and will probably install taps on my new battery to be able too measure the voltages of each group of cells directly. This way I will know if the BMS is doing its job and if the cells are healthy.

          Originally posted by adecoy95
          Well from the voltage on the display it looks like 3 days lowers charge by a volt


          • #7
            If I fully charge a pack and realize I won't be using it for several days I ride it around the block or rig a load to drain a little off the pack. Half-charged isn't as important as just NOT sitting at full SOC for long period of time. 4-4.1V /cell is enough off the top charge to be greatly beneficial, IMO.

            Parallel sense wires are great if you can do quality rework installing them. But if not or if you need to hack the case up, maybe just "trust" the BMS and allow the vendor to warranty the situation for the 1st few months of use?


            • #8
              Yup, I'll probably end-up trusting the BMS and cells after a few initial checks determine no issues. Quality cells stay in balance for years/thousands of miles without BMS. With BMS, it's anyone's guess as the BMS itself might be draining the cells unevenly when not in use. I built a Nissan Leaf-based pack with 18 cells for a Vectrix VX1 maxi-scooter, without BMS. Only bulk-charged in series, and I had access to the 36 individual half-cells in the pack that were in series. I was checking it often at first, then only once in a while. Over sveral thousand miles and a winter in storage at 40% SoS and a few more thousand miles the next year, they were still perfectly top-balanced as the day I got them. My '15 Zero SR motorcycle had BMS and it too stayed perfectly balanced for months unused in storage during winter.

              I don't know if the Panasonic GA cells in the Luna packs are as high quality as the Leaf and Zero/Farris puches, but if they are, they should not unbalance much with use. I'm curious to find out, hopefully soon - still have not received my BBSHD kit. The 14 tap points in the shark battery should be easy to add and expose via a standard R/C type 8-port connectors. I could then use a pair of cheap 8-port volt meters to check voltages periodically, or just use my multimeter for a more precise reading (in my experience the $2 voltmeters can have as much as 0.3V variance per cell, even though they are rated much better). These ports would need to be protected from the elements and potentially shorting if damaged though. They can also be used to individually balance 4-cell groups if a cell or group needs to be replaced at some point.


              • #9
                The Junsi CellLog 8 (S or M) is a very cool and accurate enough 8 ch Lipo cell checker. Always a good thing to have around with balance taps.

                I agree about BMS (murdering functions) if you suffer one with a shorted bleed transistor on a channel or two it will likely kill cells. In my experience, this happens more often than I care for.

                It would be better IMO to simply not have that lame-ass bleed balance function in the 1st place. As you realize, good cells - properly assembled, should maintain balance well enough and if there were JST’s available, simply touch up series strings SOC if/when required?


                • #10
                  Is it better to keep a battery topped off or to only charge when the charge is substantially down (what %?)


                  • #11
                    Ideally you keep it around 30-70% of capacity most of the time. You do not want to top it off unless right before a long trip. The longer it sits at 100% the more damage to the cycle life. The more full cycles the more damage as well. But if you keep it at like 80, dropping it down to 50 for one ride, then 40 for the next, before going back up to have gotten multiple rides out of a single cycle and didn't even take it into the charge percentage where cycle life gets really affected.

                    This is one of the main reasons why it is such a good idea to get a high capacity pack if possible, you have that kinda option. That sort of usage way improves cycle life.


                    • #12
                      I've been reading various FAQs, manuals, etc. There is some confusing seemingly conflicting information about the Luna Advanced Charger — the manual it comes with says to charge for 9 hours for initial charge, while other sources (like this thread) say to just charge to 100%. Which is correct? Is 9 hours necessary (I've seen discussion about balancing, etc)?


                      • #13
                        It was just a general guideline for the initial charge so we make sure no matter what capacity the pack is, it's going to hit 100%. 9 hours is not necessary if you know what you're doing.


                        • #14
                          Originally posted by paxtana View Post
                          It was just a general guideline for the initial charge so we make sure no matter what capacity the pack is, it's going to hit 100%. 9 hours is not necessary if you know what you're doing.
                          OK, two things I'm still unclear about (in my case, with the Luna Advanced Charger):

                          1. Is simply charging to 100% (58.8v, green LED on the charger) enough for an initial charge, or do you also have to wait for balance?
                          2. To balance the pack do you have to leave the Advanced Charger connected after hitting 100%?

                          In my case, in my very first charge, it hit 100% after only a few hours — but I left it connected to the advanced charger for some time after that, and it appeared that voltage was slowly dropping. I've seen other threads talk about cycles where the charger will come back on (presumably to continue balancing).

                          If it's impractical to worry about cell balancing, let me know — I come from hobby RC lipos where we use balance leads/chargers...


                          • #15
                            When it is fully charged, it will do balancing. The bms only balances when it is fully charged. Often when you are at the end of the charge cycle you may see the charger fan kick on, then off a couple seconds later, then on a couple seconds etc. This is a good indication it is balancing.
                            If you leave it plugged in after the charge cycle has completed you may indeed see voltage slowly drop since power can bleed out of the capacitors, but that's not relevant to balancing.
                            If you unplug the pack and you see voltage drop a bit after awhile that's also normal and just a bit of voltage sag, also not relevant to balancing just that your highest voltage is when it's fresh off the pack. My packs drop by about 0.4v after they been off the charger for a few hours. Others might be more, or less, depending on how the pack has been used and other factors.


                            • mrm
                              mrm commented
                              Editing a comment
                              I'd like to see some PROOF that the battery only balances after a FULL charge. I took my 52V 11.5A PF Cell Panasonic battery down to pieces as I thought It had a balancing problem. On 2 different Luna chargers (each charged different amounts to 80 and 100%) ALL banks were charged equally no matter how much (total charge) I set the charger to. On 1 charger 100% was 58.4V. On the other charger 100% was 58.6V After months of 80,90% charges, ALL banks charged evenly EVERY time at 80, 90, 100% charge. Perfect battery? NO WAY. My 8A Hobbyking brick packs out performed my PF pack in power AND range,but not in overall life. It's MY belief that the BMS in the battery packs is always balancing during charging and discharging. If the BMS wasn't doing its job (always) the packs life would be quite short. Just my observations.

                            • Kocho
                              Kocho commented
                              Editing a comment
                              I doubt these cheap BMS boards do any other balancing but top balance near full charge. A good quality battery that has been top-balanced will stay balanced over many months and many partial charge discharge cycles, unless the BMS is messed-up and unevenly discharges some banks. I think you are just seeing that the cells are performing as expected. Or maybe your charger is always charging to full regardless of the 80 or 90% setting, so some balancing is always occuring at the end of the charge?