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What size wire do I use?

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  • What size wire do I use?

    Hi everybody, this is my first real post so I hope I am posting in the right spot. I am putting together a off-the-grid solar system for my dad's RV. Currently I have 5 130 watt Sharp panels and a midnight solar classic 150. My problem is that in order to get good sun I have to put the panels 150 or 200 feet from the RV.
    My local solar dealer says that in order to have it 150 ft I need 10 gauge wire if I hooked the 5 panels up in series but I would rather have it in the 200 ft spot because they would get more sun. I have tried to use some online wire calculators but have gotten stuck in some areas such as panel voltage(I thought that they were 12 volt panels but the panels say 17.4 volts, and if I hook them up in series are they 8 amps all together because of the higher voltage or are they 8x5 amps). Any help will be greatly appreciated. Thanks guys and have a great day.

    So my question is what size wire would i need for 150 feet, and for 200 feet.

    Btw. my solar panel specs. are.
    (5) Sharp panels
    Maximum power- 130 watt
    Open circuit voltage- 21.9 volts
    Short-Circuit current-8.2 Amps
    Rated voltage-17.4 volts
    Rated current-7.5 amps

  • #2
    Your system is 12v at the end of the battery correct..

    In series and based on 9 amps.. you need a 2 AWG wire for that 150 feet.. that will get you a 3.62% loss.. which is OK..

    Better option for you.. put EVERYTHING OUT NEAR the panels in a small shed.. and then just run the 110-120 AC wire back to the house.. that will have ALOT less loss with some 12/3 (or heavier) wire coming back to the house..
    Last edited by epsgunner; 06-12-2012, 10:18 PM. Reason: didn't read the series part
    1160 watts, Midnite 150 , Xantrex SW2000

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    • #3
      Originally posted by epsgunner View Post
      Your system is 12v at the end of the battery correct..

      In series and based on 9 amps.. you need a 2 AWG wire for that 150 feet.. that will get you a 3.62% loss.. which is OK..

      Better option for you.. put EVERYTHING OUT NEAR the panels in a small shed.. and then just run the 110-120 AC wire back to the house.. that will have ALOT less loss with some 12/3 (or heavier) wire coming back to the house..
      Since the Midnight Solar is MPPT, it would be possible to run 9 amps at ~100 volts. Do you still think that #2AWG would be needed? The calculator I used suggested #8 for those conditions.
      SunnyBoy 3000 US, 18 BP Solar 175B panels.

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      • #4
        Here is the old fashion way using pencil, paper, and formula.

        CM = [22.2 x Imax x D] / Vd

        CM = circular mill area of copper wire.
        22.2 = K constant for copper wire at 60 C for DC
        Imax = 9 amps
        D = 1-way distance in feet = 150
        Vd = Voltage drop. 2% = 5 x 17.4 x .02 = 1.74 volts

        Crunch the numbers and you get 17,224 Circular Mills Cross Reference to AWG table and that works out to # 6 AWG = 26,240 cm . However #8 AWG is real close at 16510 cm and would be OK.

        Crunch the numbers for 200 feet and you get 22,985 CM and that crosses to # 6Awg @ 26,240

        Right answer is #6 AWG for both 150 and 200 feet to obtain 2% or less voltage drop.
        MSEE, PE

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        • #5
          I like the spreadsheet caculator in my .sig below. It covers the hi voltage run from the PV arrays to combiner, combiner to controller and controller to batteries, and gives total loss for all.

          And if you want to use aluminum wire for the ling runs, you just upsize 2 gauges from the copper. If it needs #6 copper, you can subsitute #4 aluminun. That was useful for my 980' run from shop to pump, to ozonater at tank farm. Just be sure the connections are rated for aluminun, and that you use the anti-ox goop on them.
          spreadsheet based voltage drop calculator:
          http://www.solar-guppy.com/download/...calculator.zip
          http://www.solarpaneltalk.com/showth...oss-calculator

          http://www.mike-burgess.org/PVinfo_2.html

          solar: http://tinyurl.com/LMR-Solar
          gen: http://tinyurl.com/LMR-Lister ,
          battery lugs http://tinyurl.com/LMR-BigLug
          Setting up batteries http://tinyurl.com/LMR-NiFe

          gear :
          Powerfab top of pole PV mount | 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

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