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23mikey's avatar
23mikey
Explorer
Aug 11, 2015

Inverter Wiring Length

Hi All,

Installing an inverter / solar / battery upgrade to my 2015 Glacier Peak 5er. This will be the 3rd system I've installed in 3 different 5ers and each one I've incorporated lessons learned and knowledge gained from this form to improve each one.

My question focuses on the wiring from the battery bank (4-6v AGM) to the inverter. Cable will be 4/0 and the batteries will be within 3 feet of inverter.

QUESTION: How critical is it to have the total length of the negative cable the same as the total length of the positive cables? I know to have balance of the battery bank will require me to take power off opposite ends of the bank. In my situation my batteries are mounted on two shelves, one on top of the other. So running the NEG cable from lower fwd batt and POS from upper rear Batt will have cable lengths 12-18 inches different. Will this cause an unbalanced condition? Should I just add an extra loop to equalize the lengths? Or am I over thinking this and it's not to worry about?

Thanks,
Mike

14 Replies

  • 2oldman's avatar
    2oldman
    Explorer II
    Aug 12, 2015
    You could go 24v or higher and make any wiring length issues moot. And you wouldn't have to deal with that monster 4/0 stuff.
  • DrewE's avatar
    DrewE
    Explorer III
    Aug 12, 2015
    MrWizard wrote:
    'Balance' is in the inter-connecting of the batteries
    so all batteries have the same applied voltage and same applied load

    the inverter/charger is a series circuit
    and if one cable is a little longer than the other, it makes no actual difference in the working of the circuit, one cable could be two or three feet longer, and it wold not affect the batteries
    the difference would be in the voltage drop across the two cable lengths under heavy inverter load, it would not affect the batteries
    or the inverter


    x2 on this.

    Keep the wires and wiring for the batteries balanced (if you have batteries in parallel). For the wires from the battery bank to the inverter, keep them as short as practical to minimize voltage drop—even if it means one is longer than the other one. There is no imbalance to worry about; you don't care if the voltage drop on the negative side is equal to that on the positive side or not, just that it's as low as practical.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Aug 12, 2015
    Hi Mike,

    The best source about balance I know is below.

    This is what is balanced and best for twin twelve volt batteries.



    As it often doesn't cost a dime more to do this, I think it is worth the trouble.

    If you wish to understand the "why" surf here:

    correctly interconnecting multiple twelve volt batteries

    Others may say it doesn't matter--but unless there is a compelling reason to not optimize charging and discharging why not do it the best possible way?

    Here is a video of 3 twelve volt batteries that have been wired in an unbalanced manner for 2 years. They have been equalized. The test shows how CCA has been adversely affected.

    unbalanced for 2 years

    23mikey wrote:
    GordonThree - I am installing a Magnum Inverter, the Hybrid. I haven't seen in the install manual Magnum talks about balance. Could you point me to where it might be? On their website maybe?

    Mike
  • wnjj's avatar
    wnjj
    Explorer II
    Aug 12, 2015
    Canadian Rainbirds wrote:
    No, there will be no imbalance IF they connect to the batteries in a balanced manner. The current through each cable will be the same. Ohms law indicates that in a series circuit the current remains the same while voltage drops across any resistance.


    Correct. The only lengths that need to match to be balanced are the short parallel jumpers between the top and bottom battery sets. The idea is the extra length to get to the negative side is canceled by the shorter length on the positive side for a given 12v battery pair and vice-versa.
  • 12thgenusa's avatar
    12thgenusa
    Explorer
    Aug 11, 2015
    MEXICOWANDERER wrote:
    Put the inverter under max load and at the same time measure voltage across terminals of all three-cell batteries. If there is a problem ot will show up as unequal voltage between batteries.

    But could that also be a function of battery health?
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Aug 11, 2015
    Put the inverter under max load and at the same time measure voltage across terminals of all three-cell batteries. If there is a problem ot will show up as unequal voltage between batteries.
  • MrWizard's avatar
    MrWizard
    Moderator
    Aug 11, 2015
    'Balance' is in the inter-connecting of the batteries
    so all batteries have the same applied voltage and same applied load

    the inverter/charger is a series circuit
    and if one cable is a little longer than the other, it makes no actual difference in the working of the circuit, one cable could be two or three feet longer, and it wold not affect the batteries
    the difference would be in the voltage drop across the two cable lengths under heavy inverter load, it would not affect the batteries
    or the inverter
  • 23mikey's avatar
    23mikey
    Explorer
    Aug 11, 2015
    GordonThree - I am installing a Magnum Inverter, the Hybrid. I haven't seen in the install manual Magnum talks about balance. Could you point me to where it might be? On their website maybe?

    Mike
  • 23mikey's avatar
    23mikey
    Explorer
    Aug 11, 2015
    Thank you guys for your input. I didn't think of it in terms of resistance/foot. You've confirmed that I was over-thinking this and you've made my install that much easier!

    Cheers!

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