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battery cable size for 24 volt battery bank 4x6v batteries

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  • battery cable size for 24 volt battery bank 4x6v batteries

    Goodafternoon, what size battery cable is best used in my situation to wire 4x 6v trojan golfcart batteries in series? (will make it 8 batteries this year)
    I have 4x240V panels, 24 V 1500 w inverter, 60 amp MPPT xantrex/schneider
    On youtube I see 2 gauge and sometimes 4 gauge. In our local Carquest I see complete battery cables 12" 4 ga. for $11, another store is able to cut and crimp 2 ga. cables for $28 each.
    If you need more info let me know.

  • #2
    Originally posted by bahamasolarnoob View Post
    Goodafternoon, what size battery cable is best used in my situation to wire 4x 6v trojan golfcart batteries in series? (will make it 8 batteries this year)
    I have 4x240V panels, 24 V 1500 w inverter, 60 amp MPPT xantrex/schneider
    On youtube I see 2 gauge and sometimes 4 gauge. In our local Carquest I see complete battery cables 12" 4 ga. for $11, another store is able to cut and crimp 2 ga. cables for $28 each.
    If you need more info let me know.
    It is all based on peak load current and cable length to maintain 2% of less voltage drops. So until you can give us those details no one can help you. Forget what you have seen on You R Screwed Tube.

    But I can get you close making some assumptions.

    Fist assumption is your panels are wired in a 2 x 2 configuration yielding 72 volts @ 14 amps on a length of cable of no more than 10 meters one-way cable distance. That would require a minimum of #12 AWG stranded copper between the panels and CC.

    The cable between the CC and battery post of no one-way length longer than 3 meters running 24 volts @ 40 amps will require to be no smaller than # 8 AWG stranded copper.

    The cable between your battery and inverter at no one-way length longer than 3 meter running 24 volts @ 65 amps will need to be no smaller than 6 AWG stranded copper wire.

    Those are the minimum sizes required to be safe and meet 2% or less voltage drop between devices. All totaled up about 5% loss on all cables. If you want to go larger you can but at extra expense.
    MSEE, PE

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    • #3
      Originally posted by Sunking View Post
      It is all based on peak load current and cable length to maintain 2% of less voltage drops. So until you can give us those details no one can help you. Forget what you have seen on You R Screwed Tube.

      But I can get you close making some assumptions.

      Fist assumption is your panels are wired in a 2 x 2 configuration yielding 72 volts @ 14 amps on a length of cable of no more than 10 meters one-way cable distance. That would require a minimum of #12 AWG stranded copper between the panels and CC.

      The cable between the CC and battery post of no one-way length longer than 3 meters running 24 volts @ 40 amps will require to be no smaller than # 8 AWG stranded copper.

      The cable between your battery and inverter at no one-way length longer than 3 meter running 24 volts @ 65 amps will need to be no smaller than 6 AWG stranded copper wire.

      Those are the minimum sizes required to be safe and meet 2% or less voltage drop between devices. All totaled up about 5% loss on all cables. If you want to go larger you can but at extra expense.
      Hi Sunking how have you been. Ok, that is good to know, your assumptions are spot on. I will change some wiring on my plan.

      But what I meant to ask was the proper gauge size of the 12 inch " jumper cables" between the
      6 volt batteries in series. They sell 4 gauge and 2 gauge.

      Comment


      • #4
        Originally posted by bahamasolarnoob View Post
        Hi Sunking how have you been. Ok, that is good to know, your assumptions are spot on. I will change some wiring on my plan.

        But what I meant to ask was the proper gauge size of the 12 inch " jumper cables" between the
        6 volt batteries in series. They sell 4 gauge and 2 gauge.
        Either will work for you. If the added cost for 2 AWG over 4 AWG is not important to you, go with 2 AWG as it handles more current with less loss.
        MSEE, PE

        Comment


        • #5
          Originally posted by Sunking View Post
          It is all based on peak load current and cable length to maintain 2% of less voltage drops. So until you can give us those details no one can help you.
          <snip>
          The cable between your battery and inverter at no one-way length longer than 3 meter running 24 volts @ 65 amps will need to be no smaller than 6 AWG stranded copper wire.

          Those are the minimum sizes required to be safe and meet 2% or less voltage drop between devices.
          My advice is to make the battery cables (between batteries and from battery to inverter) thicker than #6. If you have anything with a startup surge (such as a water pump, refrigerator, power tool, etc) you will exceed the 1500 watt rating of your inverter for a moment, and the resistance of the battery cables may prevent the appliance or tool from starting.

          You didn't mention what brand or model of inverter you are using... I have never seen an inverter that did not include a recommended cable and fuse size for the DC input.

          --mapmaker
          ob 3524, FM60, ePanel, 4 L16, 4 x 235 watt panels

          Comment


          • #6
            Originally posted by mapmaker View Post
            You didn't mention what brand or model of inverter you are using... I have never seen an inverter that did not include a recommended cable and fuse size for the DC input.
            And if you take note, most recommend too small of a cable based solely on minimum cable size to safely handle the current in Free Air from NEC tables. For low voltage we use maximum voltage drop of 2% or less. The start up surges if 2% or less is not a real issue. 2% of 24 volts = .48 volts. If we double the current momentarily the voltage loss is .96 volts or 4%.

            However with that said I have no issue using a larger cable than required if your economics can afford it. As stated I said 2% or less, and 2% can get expensive on long runs.
            MSEE, PE

            Comment


            • #7
              Originally posted by Sunking View Post
              Either will work for you. If the added cost for 2 AWG over 4 AWG is not important to you, go with 2 AWG as it handles more current with less loss.
              Ok thanks.

              Comment


              • #8
                Bob if it makes things easier for you tooling and installation wise, just use 2 AWG from the battery inter-cell connections to the inverter. Personally I do not suggest using 2 AWG from the panels to the controllers because of the expense. But if you can afford it and the equipment can actually terminate that large of a cable goferit.

                What I gave you is minimum requirements to meet 2% of less voltage loss.

                Good Luck
                MSEE, PE

                Comment

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