Upgrade Panel output cable size

boywonder
boywonder Registered Users Posts: 16
My output cable (from panels to controller) I have now is #10 with two solid wires (+ & -) in a single jacket and is sun resistant. I want to wire my two 180 w panels in series and increase the output wire size to #6 so I can replace the current length from 30' to 45'. My setup is for an RV and is portable so it needs some flexibility as I move the panels around.

Will the #6 wire have to be stranded wire??? What is a good source for purchasing the wire???? Does Home Depot or Lowe's carry such a wire??? Thanks,
boywonder

Comments

  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Upgrade Panel output cable size
    boywonder wrote: »
    My output cable (from panels to controller) I have now is #10 with two solid wires (+ & -) in a single jacket and is sun resistant. I want to wire my two 180 w panels in series and increase the output wire size to #6 so I can replace the current length from 30' to 45'. My setup is for an RV and is portable so it needs some flexibility as I move the panels around.

    Will the #6 wire have to be stranded wire??? What is a good source for purchasing the wire???? Does Home Depot or Lowe's carry such a wire??? Thanks,
    boywonder
    Why wouldn't you want to use stranded wire? I know you can get #6 bare solid (unstranded), but Table 8 in the NEC shows #8 as the largest unstranded wire.
  • boywonder
    boywonder Registered Users Posts: 16
    Re: Upgrade Panel output cable size

    Thanks for the reply. It doesn't matter to me if its stranded wire. I just didn't know if it made a difference or not. I actually figured stranded would be better for my application since it needs to be flexible wiring for rolling up and storing.
    Thanks,
    boywonder
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Upgrade Panel output cable size

    Why would you want/need to increase the cord gauge if you put the panels in series? The higher Vmp of the array (and MPPT charge controller?) would normally reduce the percentage of voltage drop a lot.

    What is the Vmp/Imp of your panels?

    You should be able to get 6awg cordage (like SO shop cord)--but it will be terribly expensive and heavy.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jagec
    jagec Solar Expert Posts: 157 ✭✭
    Re: Upgrade Panel output cable size

    In an RV installation, with its attendant bumps and vibrations, you'll want to go with stranded. ESPECIALLY if you're moving the panels.

    I'm not sure if you're going to find outdoor-rated large-gauge wire at the big box stores. You might want to check ebay, it seems to me that lots of contractors unload excess wire on there. Buyer beware, of course, but that's where I picked up the wire for my system.
  • boywonder
    boywonder Registered Users Posts: 16
    Re: Upgrade Panel output cable size

    B.B.
    Thanks for your reply.
    I have two 180 watt panels that are 24 volt and a TriStar Controller that will handle 150 volt. I'm extremely new & not knowledgeable on Solar. I was under the impression if I made a longer run of cable, I'd need to increase the size. Would changing from parallel to series on the panels and having 45' of cable, that with #10 like I have now would be large enough???
    Thanks,
    boywonder
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Upgrade Panel output cable size
    boywonder wrote: »
    B.B.
    Thanks for your reply.
    I have two 180 watt panels that are 24 volt and a TriStar Controller that will handle 150 volt. ...

    Does your tristar controller have the words MPPT on it ??

    I'd guess your panels are about 7A, so 2 in series would still be 7A @ 48V. no need to go to a larger gauge of wire. And stay with stranded.

    And don't clip off the MC connectors on the panels, use MC extender cables, and cut those. The factory MC connectors are integral to the warranty! Clip them = no warranty.
    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

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

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Upgrade Panel output cable size

    Vmp is Operating Voltage at maximum power, and Imp is operating current at maximum power.

    If you have Vmp=24 volt panels (need to really check the label--there is Voc or voltage open circuit which is different and higher than Vmp):
    • 180 watts / 24 Vmp = 7.5 amps Imp
    So, two panels in series would be Vmp-array = 48 volts and Imp-array = 7.5 amps.

    Ideally, we want a maximum of 3% voltage drop, and usually 1% minimum (you can go lower, but the copper costs are very high). Using a generic voltage drop calculator, we see:
    • 3% * 48 volts = 1.44 volt maximum drop
    • 1% * 48 volts = 0.48 volt minimum cost effective voltage drop
    And from the calculator:
    • 50 feet one way run; 12 awg wire => 1.4 volts drop
    • 50 feet one way run; 10 awg wire => 0.9 volts
    • 50 feet one way run; 8 awg wire => 0.6 volts
    • 50 feet one way run; 6 awg wire => 0.4 volts
    So, realistically, any cordage with 12 awg to 6 awg will work fine. Running the panels in series really helps reduce the awg requirements (something like 6 awg smaller gauge if you put the two panels in series vs two panels in parallel).

    Copper wire does work harden--so stranded wire will last longer if you move the cables/wrap them up for moving between sites often. The finer the strands, the less work hardening will occur.

    - Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Upgrade Panel output cable size

    much of this was already discussed here,
    http://forum.solar-electric.com/showthread.php?t=13013

    if he stays with paralleled pvs he'll want the thicker wire, but if he succeeded in placing them in series he could extend it with #10.
  • boywonder
    boywonder Registered Users Posts: 16
    Re: Upgrade Panel output cable size

    Mike90045,
    Thank you for the reply. My TriStar Controller is MPPT 45amp. The guy that set this up for me put in a junction box below the panels and with quick connects between the panels and the junction box. Inside the junction box he spliced the wires together so there will be no need for me to alter the connectors. Inside the junction box is where I'll do the changeover from parallel to series.

    I will go with stranded cable for flexibility and will either stay with 10awg or go with 8awg max.
    Thanks,
    boywonder
  • boywonder
    boywonder Registered Users Posts: 16
    Re: Upgrade Panel output cable size

    Neil & B.B.,
    Thanks for your replies and your help. It's a "go" with stranded wire (I'll be rolling and un-rolling it quite often) and I'll keep it at 10awg or go to 8awg max. Now I just need to find me a source for the wire. Looks like I may have to go with two separate wires ( one +, one -) and tape them together.
    Thanks,
    boywonder
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Upgrade Panel output cable size

    I saw Home Depot had some 10 gauge extension cords for like an RV hookup pretty reasonable.