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Cable size formula for solar panel wiring

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  • Cable size formula for solar panel wiring

    Hello, so i plan to install 3 of this 310w panels in parallel (watch picture) on my boat and im not sure about the wiring size. Cable lenght from the panels to controller will be around 30ft.
    reason for parallel wiring is shading. Controller is a midnight solar 150.
    What formula is existing to get as less voltage drop as possible?
    Attached Files

  • #2
    Looks like you could have just 30 A from the 3 panels in parallel. That would require at least 10ga wire, adding that distance, I'd opt for 8ga. Harder to wrangle and pull, but it would give the least loss. With more than 2 panels, you need a Combiner Box or some other way for panel protection if a panel becomes damages so it does not start a fire.
    Last edited by Mike90250; 07-13-2021, 07:23 PM. Reason: grammar correction
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

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    • #3
      When laying the wire, I’d recommend you making it thicker than you need to account for growing, On top of thicker wire, if you put it in conduit, make it big enough to fit more wire.

      I go to here and figure about wire with less than 3% losss:

      https://www.calculator.net/voltage-drop-calculator.html

      I also check the amps running through the wire and make sure its good for less than 60 Degrees C insulation:

      https://www.wireandcabletips.com/what-is-ampacity/

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