Cable assumptions

stmoloud
stmoloud Registered Users Posts: 111 ✭✭
edited December 2018 in Solar Beginners Corner #1
Skimming over previous posts here on this fantastic forum I feel confident enough to make some cable size assumptions:
Max panel current is 42.3 amps so 45 amp controller will be up to task
I can use 56 amp-rated cable for all series-parallel battery interconnections (equal lengths), also 56 amp from batteries to controller , and 56 amp from solar distribution bars to controller(equal lengths). 
I can't use different cable sizes for battery interconnections. For instance I have 200 amp cable but this will not play well with the 56 amp cable, even if the same length. 
Thanks, I'm sure someone will respond if I'm wrong here.
760W panel array, 4 x 6v 220 ah Crown batteries, Tristar TS-45 PWM controller,  no name 600 PSW inverter. 
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #2
    The main thing is to size overcurrent protection devices (fuses and/or breakers) for the most vulnerable part of the circuit.  You could include 200a wire, as long as the OCDs are sized to protect the 56a (although you wouldn't want to use a mix of wire sizes for parallel battery connections).

    56a wire seems on the light side for battery wiring.  Although it may be adequate for pv charging current, what about discharging? Will you have an inverter, and if so, how big.  Will you have other charging capability (eg generator and AC charger), and if so, how big?
    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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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #3
    The charging source  is different from the dischargeing source, from the battery  to inverter use the largest conductors possible,  this includes all interconnects, the charging  source must have conductors sufficiently sized to allow minimal voltage drop, ultimately the larger the better applies in all circumstances,  over current protection  can be less than the conductors maximum capacity rating, but not more.
    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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  • stmoloud
    stmoloud Registered Users Posts: 111 ✭✭
    #4
    Longest length of setup is about 8 foot so minimal voltage drop. I am using the cable supplied with the inverter so am assuming that the size is correct. No, I won't have any other charging capability, only solar.
    Estragon, just to clarify - it would be OK to mix cable sizes on the series part of the battery interconnects?


    760W panel array, 4 x 6v 220 ah Crown batteries, Tristar TS-45 PWM controller,  no name 600 PSW inverter. 
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  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    #5
    Yes  different size cables ok on the series interconnects ... fuse or circuit breaker needs to be sized for the smallest size cable.
     However.....Biggest  cable you can fit is best on battery leads.
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
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  • stmoloud
    stmoloud Registered Users Posts: 111 ✭✭
    #6
    OK thanks. I will wire my 200 amp battery interconnects in series, the 56 amp in parallel. Yes agree bigger will be better but due to budget constraints 'enough and only just' will have to do it for now.  
    760W panel array, 4 x 6v 220 ah Crown batteries, Tristar TS-45 PWM controller,  no name 600 PSW inverter. 
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