Whats the best way to wire my battery bank to draw from and charge.

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rgearhead
rgearhead Solar Expert Posts: 38 ✭
in Solar Beginners Corner #1
I have 6 -6volt batteries wired series - parallel to feed a 12 volt Inverter... and the way it is wired series -parallel now im pulling +pos and -neg from opposite corners of the bank and charging them the same way= opposite corners of the Bank ...

but I am noticing draw swing, if i have my garage floor fan running (pulls 2.5amp's) for a few hours and look at the volt gauge near the inverter, I Might see the voltage is getting down to 12.3 volts at the inverter , so I shut the fan and Inverter off, but if i check the volt gauge 10 minutes later voltage is back showing 12.6 just from resting..

so im wondering if I was to lift(un link ) the parallel between each 2 batteries in series and just bring them to one common +pos lug and -neg lug and link it up there for draw and charge, would it be smoother? work better ?


Thanks Bob....
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #2
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    Re: Whats the best way to wire my battery bank to draw from and charge.
    rgearhead wrote: »
    I have 6 -6volt batteries wired series - parallel to feed a 12 volt Inverter... and the way it is wired series -parallel now im pulling +pos and -neg from opposite corners of the bank and charging them the same way= opposite corners of the Bank ...

    but I am noticing draw swing, if i have my garage floor fan running (pulls 2.5amp's) for a few hours and look at the volt gauge near the inverter, I Might see the voltage is getting down to 12.3 volts at the inverter , so I shut the fan and Inverter off, but if i check the volt gauge 10 minutes later voltage is back showing 12.6 just from resting..

    so im wondering if I was to lift(un link ) the parallel between each 2 batteries in series and just bring them to one common +pos lug and -neg lug and link it up there for draw and charge, would it be smoother? work better ?


    Thanks Bob....
    I am guessing the 2.5 amps is AC, it will be pulling 25 amps or so DC amps. The voltage sag is perfectly normal. What your seeing is Dip and Recovery.( Coupe de Foret ). Don't know the size wiring to the Inverter, that will cause sag also and some is just the nature of deep cycle batteries.

    When I set up any GC-2 banks above 4 batteries I always use 4/0 cable for all interconnects. It costs a little more, but worth it.
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  • rgearhead
    rgearhead Solar Expert Posts: 38 ✭
    #3
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    Re: Whats the best way to wire my battery bank to draw from and charge.

    yes'' the fan draws 2,5 amps AC, from the inverter, Im just wondering if it would ba a smoother draw n charge to the batteries if i re wire like i said above or is it not worth changing the way it is right now..

    the Batteries are wired with 1 ot' series-parallel and im running 2 gage to the inverter 4 feet away ...
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: Whats the best way to wire my battery bank to draw from and charge.

    There would be a small current sharing improvement if all batteries were wired to common points for negative and positive with equal size & length wire. See drawing (ignore the number of batteries per string: it was done for a 48 Volt system).

    You should not be suffering severe Voltage sag at 12 Volts, 25 Amps on 2 AWG with a 4 foot run. Check the Voltage difference under load at each battery string and at the inverter.
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  • rgearhead
    rgearhead Solar Expert Posts: 38 ✭
    #5
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    Re: Whats the best way to wire my battery bank to draw from and charge.

    yep''' that's what im talkin about Cariboo, the sag takes time.... the fan can be on for Hours and as i walk by the volt meter mounted near the inverter i Slowly see it dropping ( over time ) to say 12.3 volts and if i check it at the battery terminals where the inverter draws from it reads a tenth or 2 higher than the gage shows.... but then if i shut it down and leave it rest, volts come back to 12.6ish...

    thanks....
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #6
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    Re: Whats the best way to wire my battery bank to draw from and charge.
    Blackcherry04 wrote: »
    I am guessing the 2.5 amps is AC, it will be pulling 25 amps or so DC amps. The voltage sag is perfectly normal. What your seeing is Dip and Recovery.( Coupe de Foret ).
    Actually Coup de Foret refers to a rapid dip and then recovery when first turning on a constant load after the batteries have been on charge. It has nothing (much) to do with voltage recovery after the load is disconnected. And it is a phenomenon peculiar to lead acid batteries AFAIK.

    A recovery of voltage at the battery terminals after the load is disconnected is the result of internal resistance and some other chemical processes going on in the plates and the electrolyte.
    SMA SB 3000, old BP panels.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
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    Re: Whats the best way to wire my battery bank to draw from and charge.
    inetdog wrote: »
    Actually Coup de Foret refers to a rapid dip and then recovery when first turning on a constant load after the batteries have been on charge. It has nothing (much) to do with voltage recovery after the load is disconnected. And it is a phenomenon peculiar to lead acid batteries AFAIK.

    A recovery of voltage at the battery terminals after the load is disconnected is the result of internal resistance and some other chemical processes going on in the plates and the electrolyte.
    Nice to know, I always thought when a Battery dropped in voltage and recovered it was called Dip and Recovery. Do you have a correct term ?
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
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    Re: Whats the best way to wire my battery bank to draw from and charge.
    Blackcherry04 wrote: »
    Nice to know, I always thought when a Battery dropped in voltage and recovered it was called Dip and Recovery. Do you have a correct term ?

    I usually call it voltage sag and rebound :roll: but that isn't necessarily the correct term. "Coupe de fouet" (not "Coup de Foret") is a much more rapid phenomenon and the recovery occurs while the battery is still under load. Measurement of the Coupe de fouet effect can be used to predict the health of some types of battery. Plenty of links on google.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #9
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    Re: Whats the best way to wire my battery bank to draw from and charge.
    vtmaps wrote: »
    I usually call it voltage sag and rebound :roll: but that isn't necessarily the correct term. "Coupe de fouet" (not "Coup de Foret") is a much more rapid phenomenon and the recovery occurs while the battery is still under load. Measurement of the Coupe de fouet effect can be used to predict the health of some types of battery. Plenty of links on google.

    --vtMaps
    Let's just stick with Voltage dips and then recovers, happens happens even time I have a load on and shut it off.
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