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Would two bank of battery share one comman negative cable cause any problem?

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  • Would two bank of battery share one comman negative cable cause any problem?

    Hi guys,

    I have two 48 volts bank battery wired in parallel to service my Magnum MS4448PAE inverter, each battery bank have it own positive cable connected to a midnite disconnect breaker box. How ever they shared a common negative cable to the inverter.

    I have connect the IOTA charger to one bank through the positive cable on the disconnect breaker on the battery side. I turned off the breaker so the inverter won't draw any current from this bank.

    I have the other bank battery supply power to the inverter, the inverter is supplying the house with minimum load at the night. how ever because the two bank are share the same negative cable in the inverter room, the measurement of the current on the negative cable measure only 3 amperes, the charger is charging one bank with 8+amps and the inverter draw about 12 amps from other battery bank, will this setup cause any problem for sharing the common negative cable?

    Thanks.

  • #2
    Originally posted by paulcheung View Post
    Hi guys,

    I have two 48 volts bank battery wired in parallel to service my Magnum MS4448PAE inverter, each battery bank have it own positive cable connected to a midnite disconnect breaker box. How ever they shared a common negative cable to the inverter.

    I have connect the IOTA charger to one bank through the positive cable on the disconnect breaker on the battery side. I turned off the breaker so the inverter won't draw any current from this bank.

    I have the other bank battery supply power to the inverter, the inverter is supplying the house with minimum load at the night. how ever because the two bank are share the same negative cable in the inverter room, the measurement of the current on the negative cable measure only 3 amperes, the charger is charging one bank with 8+amps and the inverter draw about 12 amps from other battery bank, will this setup cause any problem for sharing the common negative cable?

    Thanks.
    No.

    There will be some voltage drop in the common negative based on current through the other bank, and if your charger does not use remote voltage sensing leads it might cause some voltage offsets, but probably not enough to do any harm.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      which bank will have voltage off set (drop)? the charging bank or the discharging bank?
      Thanks

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      • #4
        Paul no problem with having the battery Negative polarity common as that is the way it is suppose to be done. As long as you disconnect the positive terminal of the battery in question, you can charge it sepeartely.

        However when you reconnect the battery sparks can and will fly if the voltages are not equal.
        MSEE, PE

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        • #5
          Thank you Dereck,
          I use the 250 amps breakers to connect and disconnect the strings so I won't see the sparks, but I still make sure the voltage between the two bank are not too far, I normally use the inverter to draw down the voltage on the higher voltage string to the lower one, when I connect the two bank together they won't cause too much excitement.

          Thanks again.

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          • #6
            Originally posted by paulcheung View Post
            Thank you Dereck,
            I use the 250 amps breakers to connect and disconnect the strings so I won't see the sparks,
            Don't kid yourself Paul, a battery can vaporize a 250 amp breaker if there is a significant voltage difference and the battery has some high capacity rating. In telecom we use motor/spring 2000 amp disconnects, and closing the circuit with as little as 1 volt difference will weld the contacts together. Those disconnects are as large as a suitcase. Keep the voltage difference to 1/4 volt or less and be careful.

            I would really hate to hear and break my heart if you got injured or burned anything up.
            MSEE, PE

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            • #7
              Ok Sir. I will.

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