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    China Battery testing

    Hello Everyone,
    I am new to the group to ask this question as this behavior seems odd to me.

    I just picked up a 48v Battery Pack from China. There is something that seems weird to me, please let me know what you think.

    The Battery has a Keyed switch.

    Switch On - The battery output reads around 48V as expected. The charging port will also show around 48V.

    Switch Off - The battery output reads around 24V, the Charging port reads around 24v.

    The manufacturer says it is Virtual Voltage or Thermal Voltage. I can not find anything on these two terms that could be related to a battery pack.


    Any ideas on what is happening or is this normal?

    Best thing I have found that could explain it would be residual voltage in the BMS, i will test later today to see if I can bleed it off with a light bulb.

    #2
    That's a common behavior from a switched bms. Not exactly ideal, but not a defect if that's what you're asking.

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      #3
      There is leakage current - very normal.. I'd bet if you put any kind of load on it (even a little flashlight bulb) it will drop way down

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        #4
        Cool, thanks for the confirmation! It had me worried and the china tech told me I worry too much :) Is it due to a cheaper BMS? and is there anything I should watch out for.
        The reason i am so jumpy is I have seen and tried to put out my neighbors garage when his Battery Pack shorted. It's amazing how bright the 18650 cells are when they explode.

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          #5
          If I were to wage a guess my money would be that the keyed switch controls a MOSFET to turn "off" the battery and that it is leaking the current. They typically leak a few microamps but that's all it takes if there's nearly no load - just like MOSFET's all leak something when "off", any part on the output side will also leak some "load" current...

          If I were the engineer I might deliberately drain some current in the milliamp range [or less] but it's not a big deal if it's what I'm suggesting

          But that's just my best guess so take it for what it's worth =]

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