Question on correct battery cable arrangement

learaviator
learaviator Registered Users Posts: 11 ✭✭
in Off Grid Solar & Battery Systems #1
Hello everyone, new guy here. Long time mechanic and lover of all things electrical especially problems LOL but this whole battery series parallel thing for some reason is kicking my butt .... is this the correct way to wire up the batteries so that the battery usage and charging is equal?
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #2
    I can't follow it... but no...lol

    Just make strings of 4 - 6 volt batteries. This is your 24 volt system, now connect each string to a common point all positives to one all negatives to another. Use the same gauge and length wire between each battery and from the batteries to the common point.

    The idea is for the current to pass through the same amount of wire from the beginning point, through each string and to the end point. The should ensure that each battery has roughly the same resistance through each string so that the load and charging is shared equally.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,615 admin
    #3
    Note that the two + and - leads do not have to be the same length from the battery bank to the loads/charger/AC inverter DC input. You want to keep battery leads, in general, short and heavy to reduce voltage drop. (As PhotoWhit typed, you want the battery interconnects to be the same length between String A, B, and C and to the common bus connection points + and -). If one string has very long series connection(s), the higher resistance will lessen the charging and discharging current to that string).

    Given that you are designing a 24 volt system, the voltage drop is a bit less of a problem vs 12 volt systems.

    You can look at this website for some ideas about paralleling battery strings:

    http://www.smartgauge.co.uk/batt_con.html

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    edited May 2018 #4
    And most importantly - use a clamp on ammeter to verify that you have equal current flow under load and charging (from paralleled sections).   

    I am available for custom hardware/firmware development

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  • learaviator
    learaviator Registered Users Posts: 11 ✭✭
    #5
    Thanks for the replies everyone, and that article is definitely what I was looking for. I had seen it once before but could not find it. Thank you again.
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