45 watt solar panel wiring, battery to far away? Wire gage?

YostFMXYostFMX Solar Expert Posts: 94 ✭✭✭
in Advanced Solar Electric Technical Forum #1
I have a new Harbor Freight 45 watt solar panel on my motorhome and am doing the wiring (16 gage). The controller that comes with it is mounted right above the door (door is a right behind the cab) very close to the panel itself so thats no problem, but now to get to the battery from the controller is about 20' of wire! Is that going to cut the power I'm getting from the panel? I could if I really have to remount the battery closer, but its still 16' of wire to get it there. The other thing is, in the solar kit it has battery wires in it but they'er only 3' long and 18 gage, I'm using 16 gage.

I really don't know very much about wiring/power loss over wiring
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  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    #2
    Re: 45 watt solar panel wiring, battery to far away? Wire gage?

    Generally, it is better to mount the controller close to the battery bank... 1. because the voltage loss is less (controller can more accurately measure the voltage) and 2. because the controller should be temperature compensated (output voltage goes up as the battery bank gets colder)--so it can be at the same temperature as the batteries themselves.

    Regarding voltage drop--take a look at this thread. There is an Excel spreadsheet you can use to calculate the voltage drop of wire runs... Remember, the length of wire is 2x the run length (both positive and negative wires).

    And, lastly, make sure you use appropriate sized fuses nearest the source of greatest power (i.e., close to the battery + bus).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mike95490mike95490 Solar Expert Posts: 9,363 ✭✭✭✭✭
    #3
    Re: 45 watt solar panel wiring, battery to far away? Wire gage?

    with only a 45W PV panel, I doubt you will have enough amps to get much of a voltage drop. On a sad note, from Harbor Freight, it may not even work.
    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 ,

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  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    #4
    Re: 45 watt solar panel wiring, battery to far away? Wire gage?

    I had 2 sets of those HF 45Watt kits, if the charge controller is the one with just a couple of LEDs. Watch it for the first couple of days. That one is TOTAL junk. The better on has a digital display. I had it charging a 55AH battery that ran some LED lights at night. If you manage you loads, they will keep the battery charged.
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  • YostFMXYostFMX Solar Expert Posts: 94 ✭✭✭
    #5
    Re: 45 watt solar panel wiring, battery to far away? Wire gage?

    Thanks all, I know HF is crappy stuff, yes the controller does have a digital display. Hope it all works... Someone told me to use 10 or 12 gauge, it 17 feet as the wire travels to the battery.
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  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
    Re: 45 watt solar panel wiring, battery to far away? Wire gage?

    yostfmx,
    with #12,
    .16244v dropped for 1.354%
    with #10,
    .10218v dropped for .852%

    i see no problem with either wire gauge.
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