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Thread: O.T. DIY battery pack BMS problem

  1. #11
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    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.

  2. #12
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    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.

  3. #13
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    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!

  4. #14
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    Quote 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.

  5. #15
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    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

  6. #16
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    I still think you should test the charging part of the bms. The schematic that Paul posted, protects the battery in both directions. If your motor controller protects from overdischarge, you can power direct from the battery terminals and just use the bms for the charge process
    Helder Ferreira
    Setúbal, Portugal

  7. #17
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    The motor controller cannot protect an individual cell from over discharge. These cell are not matched or aged together...

  8. #18
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    There are some bms designs that monitor individual cell voltages during discharge. When one cell gets down to a preset voltage, discharge is done.

    Ed
    For just a little more, you can do it yourself!

  9. #19
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    Quote Originally Posted by lakeside53 View Post
    The motor controller cannot protect an individual cell from over discharge. These cell are not matched or aged together...
    Actually the cells are somewhat matched. I drain tested every cell, and these are the cream of the crop. But I do
    understand Lakeside, that good doesn't mean matched. But doesn't the discharge control only let it drop down to
    about 40v from the fully charged 52v ?

    Besides it is what it is. I paid a dollar a pound for these and like I said every battery in this pack checked out
    to 2800 ma hr or higher which is pretty respectable.

    I appreciate Paul doing that analysis and just hope a balancing bms will give me some life.
    John Titor, when are you.

  10. #20
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    Something is bugging me. Why would this bms have circuitry going to all 13 strings if it is not
    balancing. If all it is doing is monitoring total charge and discharge it only needs to connect to
    the + and - .

    Was thinking about it in the shower .. lol.
    John Titor, when are you.

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