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O.T. DIY battery pack BMS problem

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  • O.T. DIY battery pack BMS problem

    Ok, got the welder modified, works fine.

    Built my 48v battery pack.

    This is my first battery pack with a battery maint system so I am not
    sure of what the characteristics should be.

    When I measure voltage from the opposite ends of the battery pack excluding
    the BMS, I get the predictable 52v.

    But when I measure the output of the BMS, I only get 34v

    Ive heard talk about programming the BMS and not sure what they mean
    by that. Maybe I have to throw the charger on it, and that tells the BMS whats
    going on. There were no instructions for this thing, and I am assuming that I
    hook the charger up to the output contacts.(Those 2 holes on right side of pcb)

    Anyways .. looking for some advice.



    John Titor, when are you.

  • #2
    I know that some BMS's handle charge and discharge. In that they cutout the battery from the load/charger. Others just manage the charge and the load is connected directly to the battery terminals. This way, the motor controller is responsible for the low battery cutout. Looks like your case it just handles the charge and the reading you get at those terminals does not have to do with the battery's voltage.
    Helder Ferreira
    Setubal, Portugal

    Comment


    • #3
      You appear to have 7 strings of 12 cells in parallel. Assuming that each string is 4.8 volts, then 7 of them in series gives you 33.6 volts.

      I'm not sure how you are getting "from opposite ends of the battery pack" when the strings are in parallel. It would seem that you need 11 strings in series to get 52 volts.

      Dan
      At the end of the project, there is a profound difference between spare parts and extra parts.

      Comment


      • #4
        Originally posted by Noitoen View Post
        I know that some BMS's handle charge and discharge. In that they cutout the battery from the load/charger. Others just manage the charge and the load is connected directly to the battery terminals. This way, the motor controller is responsible for the low battery cutout. Looks like your case it just handles the charge and the reading you get at those terminals does not have to do with the battery's voltage.
        That really makes sense, but I think/hope you are wrong. I would think what you are describing is a
        charge controller, while this is a true bms. This also limits the discharge to keep the batteries healthy.
        But I am definitely going to recheck that.


        Originally posted by danlb View Post
        You appear to have 7 strings of 12 cells in parallel. Assuming that each string is 4.8 volts, then 7 of them in series gives you 33.6 volts.

        I'm not sure how you are getting "from opposite ends of the battery pack" when the strings are in parallel. It would seem that you need 11 strings in series to get 52 volts.

        Dan

        Actually, this configuration is called a 13s 6p. There are 13 strings of 6 parallel.

        I can put my meter on the ground and in turn, touch each string, nicely progressing up to the 52v in
        4v increments.

        Someone on an E-bike forum answered me and said that it might just need to be cycled. I get my
        charge in a couple days and will try that.

        The only thing I am worried about is that for a couple of the pcb contacts, I used the spot welder and
        and I hope I didn't fry anything doing that.

        Again, here is the link to the bms, and now Noitoen has me worried, lol, it does say bmscharger.

        https://www.aliexpress.com/item/13S-...1f016857xVnICA
        John Titor, when are you.

        Comment


        • #5
          13s 6p is what I see too.
          Helder Ferreira
          Setubal, Portugal

          Comment


          • #6
            Can be a bms charger and if so, you have to supply a suitable voltage/current to those bms terminals.
            Helder Ferreira
            Setubal, Portugal

            Comment


            • #7
              I don't recon the battery will last long without the cells being matched.

              Comment


              • #8
                Lithium chargers typically start with a constant current mode where the charger adjusts it's voltage to whatever is required to get to the target current.
                For just a little more, you can do it yourself!

                Comment


                • #9
                  Originally posted by old mart View Post
                  I don't recon the battery will last long without the cells being matched.
                  The bms should distribute the charging voltage equally between the cells in series. Any difference in cell internal resistance will be corrected this way
                  Helder Ferreira
                  Setubal, Portugal

                  Comment


                  • #10
                    With series lithium cells, all will of course see the same current. However, they won't necessarily charge at the same rate. When one of them reaches it's full charge, measured by it's voltage, the charger has to stop to avoid overcharge of that cell. Good chargers may go then go into a balance phase where the fully charged cell is dscharged a little, and the cycle repeats.

                    Er
                    Last edited by ed_h; 03-13-2019, 08:22 PM.
                    For just a little more, you can do it yourself!

                    Comment


                    • #11
                      Well I think the bms is shot.

                      I figured I would hook a light load up to the bms outputs and get it to do some work.

                      well ... it may show 34v but it has nothing behind it, wouldn't even turn a little bitty motor.

                      when I hooked it up to the batteries excluding the bms, the motor spun fiercely.

                      Ordering a new bms.
                      John Titor, when are you.

                      Comment


                      • #12
                        From the customer feedback:

                        BMS mean battery management system and will manage the battery: charging and discharging per series. this BMS Don't do that, this is not a BMS, is a PCM: protection control module. I will not advise anyone to buy this, your pack will end unbalanced. I will also open a dispute.
                        The manufacturer website does not show the protection PCB:
                        http://annpower.diytrade.com/

                        I found a balancing BMS that might be better:
                        https://www.aliexpress.com/store/pro...1e9d567efdJTEi



                        Lots of alternatives on eBay, but nothing quite like yours:

                        https://www.ebay.com/sch/i.html?_fro...um+battery+bms

                        Can you take some detailed close-ups of your PCB? It might be possible to discern the general circuitry.
                        http://pauleschoen.com/pix/PM08_P76_P54.png
                        Paul , P S Technology, Inc. and MrTibbs
                        USA Maryland 21030

                        Comment


                        • #13
                          Yes, you can tell quite a bit by looking at the PCB. For example in the pic in Paul's post, the 13 black rectagle things near the connector are probably the load resistors used to discharge selected cells during the balancing phase.
                          For just a little more, you can do it yourself!

                          Comment


                          • #14
                            Originally posted by PStechPaul View Post
                            From the customer feedback:

                            The manufacturer website does not show the protection PCB:
                            http://annpower.diytrade.com/

                            I found a balancing BMS that might be better:
                            https://www.aliexpress.com/store/pro...1e9d567efdJTEi

                            Can you take some detailed close-ups of your PCB? It might be possible to discern the general circuitry.
                            Damn Paul, Don't know where you found all that. Looks like I may end up in better shape not being able to use it.
                            I see the spec sheet says nothing about balancing, so thanks so much for bringing that to my attention.

                            That bms you linked to looks perfect. I may try to find a similar one on the bay, just so I don't have to wait
                            a month for it.

                            Here's a couple pics of the bad one if you want to have a look. I accidentally took the B2 pad right off the pcb
                            while unsoldering.



                            John Titor, when are you.

                            Comment


                            • #15
                              Hard to tell exactly how this circuit is supposed to work, but basically there are four current sensing shunts on the negative side of the battery pack (B-), then a bank of four parallel MOSFETs in series with another MOSFET to the (P-) terminal. The (P+) terminal connects to the top of the battery pack (B13). I found a similar circuit schematic, although it does not have a current sensing shunt:

                              http://www.large-battery.com/lithium...n-circuit.html



                              Some more information:

                              https://batteryuniversity.com/index....thium_ion_safe

                              https://electronics.stackexchange.co...-series-revers

                              https://www.instructables.com/id/My-protection-circuit/

                              http://www.ti.com/lit/ml/slyp087/slyp087.pdf

                              http://www.lygte-info.dk/info/batter...tion%20UK.html
                              http://pauleschoen.com/pix/PM08_P76_P54.png
                              Paul , P S Technology, Inc. and MrTibbs
                              USA Maryland 21030

                              Comment

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