Help with wire length to load

n_yohan
n_yohan Registered Users Posts: 4 ✭
edited June 2017 in Off Grid Solar & Battery Systems #1
I'm confused. Please see picture below...

 I have three 12v batteries in parallel like below.  The wires going from each battery are the same length but my question is about the wire length going to the Load, also the charger.

Questions
1. Should the wires be the same length going to the load like B or shortest path like A?
2. Same question but this time the length of wires going to the charger..
3. I have a solar charger, AC charger/inverter, and of course the load.  Is it ok to have all three use a common path back to the battery bank (in the picture imagine the Load box as a common point that all three are wired to solar charger, inverter, load) or should they all have their own set of wires all the way back to the battery terminals?

Thanks so much for your help!!!



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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    1 Positive and negative same length as in B
    2 Same applies equal  length to the same terminals as load.
    3 Common point is fine

    Don't forget protection, fuses/circuit breakers
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
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  • Solray
    Solray Registered Users Posts: 246 ✭✭✭
    #3
    Sort of like both. As short as possible and equal lengths. Avoid loops and coils.
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  • rgk1
    rgk1 Solar Expert Posts: 135 ✭✭✭
    #4
    While on the subject, does the same rule apply if the batteries are in series?
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #5
    rgk1 said:
    While on the subject, does the same rule apply if the batteries are in series?

    Same rules, position your batteries in a U rather than a straight line to keep your conductors as short as possible.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • Horsefly
    Horsefly Registered Users Posts: 476 ✭✭✭✭
    #6
    rgk1 said:
    While on the subject, does the same rule apply if the batteries are in series?
    Think of it this way: If batteries are parallel, you want the path from any battery out to your loads and back into that same battery to be the same length across all batteries. So the larger + and - wires don't have to be the same length, but the way you position the batteries so that the interconnects make it so each battery has the same path length is what is important.

    If you batteries are in series none of that matters, since every electron will have to travel the same distance out of the bank, around the loop, and back to the same battery.  You don't need to worry about any wires being the same length.

    In both cases you want the total length of the wires to be as short as possible just to minimize resistive losses.

    @BB. has posted a link several times that provides a good explanation of how to wire batteries in parallel.

    Steve
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 8S (25.6V), 230Ah Eve LiFePO4 battery in a custom insulated and heated case.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #7
    A is fine. B is not needed and not useful.

    Here is a good link that explains the various parallel battery connection options:

    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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  • Horsefly
    Horsefly Registered Users Posts: 476 ✭✭✭✭
    #8
    I should add: With three batteries connected kind of like you show in either diagram (like I said, either is fine), the middle battery has to deal with a slightly greater loss in the cabling than the ones on either end. It won't be much, assuming the cables between the batteries are plenty big and as short as possible. But the center battery will deliver slightly less current to the load than the other two. The only way to avoid that is to have all three batteries have the same short cables going to positive and negative buss bars, and have the longer cables to the load connect to the buss bars.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 8S (25.6V), 230Ah Eve LiFePO4 battery in a custom insulated and heated case.
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  • Solray
    Solray Registered Users Posts: 246 ✭✭✭
    #9
    BB. said:
    A is fine. B is not needed and not useful.

    Here is a good link that explains the various parallel battery connection options:

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

    -Bill

    'A' would be a lot better if the bank was set up parallel to the load instead of perpendicular. There is no good reason to have one of the batteries so far away.
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  • n_yohan
    n_yohan Registered Users Posts: 4 ✭
    #10
    Solray said:
    BB. said:
    A is fine. B is not needed and not useful.

    Here is a good link that explains the various parallel battery connection options:

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

    -Bill

    'A' would be a lot better if the bank was set up parallel to the load instead of perpendicular. There is no good reason to have one of the batteries so far away.
    The reason the batteries are lined up like that is that they are in a camper van and there is some unused space that can fit three batteries end to end.

    If I had more space I would do it like you suggest.
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #11
    You want to keep the circuit as short as possible. 'A' is as short as possible. 'B' adds wire for no good reason.

    Even if you turn the load, you might double the positive and half the negative, and still end up with the same amount of wire. I don't see how it makes any difference.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
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  • Solray
    Solray Registered Users Posts: 246 ✭✭✭
    #12
    If you can end up with a shorter total length it does make a difference.
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #13
    Shorter total (circuit) length, yes. Whether the + or - is longer than the other, no?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • Solray
    Solray Registered Users Posts: 246 ✭✭✭
    #14
    Estragon said:
    Shorter total (circuit) length, yes. Whether the + or - is longer than the other, no?
    No. :)
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