Forum Discussion

Aluminum_Siding's avatar
Aluminum_Siding
Explorer
Dec 07, 2015

Solar Question

Hi Folks

First off thanks for the years of helpful replies!

I'm installing solar panels. I can mount my panels on the roof in front running the wiring down to the controller in the storage compartment. From the panels to the controller would be about 15 feet then from the controller to the batteries will be 2 feet.

The second option and would be way more convenient allowing for way better panel placement eg. less potential shading in the late day from one one panel a few feet in front of the other (tilt) or the shroud from the AC etc. It would be on the rear of the roof dropping the cables down only about 10 feet to the charge controller then a couple of feet to the trailers charger. I'd tie in the battery leads to the positive and negative on the back of the trailer's charger that go to the battery. These are pretty thick wires roughly 8 AWG. I understand the first scenario would most likely give me less drop.

My questions is, I've seen several vids and how to's where they tie into the battery wires connected to the trailer's charger and use those wires to transfer the power from the controller back to the batteries. Will the loss due to the distance be of any significance. Is this a recommended way of hooking up. Lets say 8 awg at 20 feet from the trailers charger to the battery bank. Also I have two 6v at 235 amp hrs. I'm only installing 2 100 wt mono panels with tilt brackets. (we dont full time or use any major appliances so this is plenty we actually did pretty well on a 100 wt portable suitcase) Anyway thanks.
  • Still_Searchin_'s avatar
    Still_Searchin_
    Explorer
    Dec 11, 2015
    FWIW: my bluesky controller has a digital readout of battery voltage, and that is really useful to monitor. I had solar dealer mount two panels close to front of trailer and 10 gauge wires came down to controller mounted in front closet where I can easily see voltage. 8 gauge from battery to junction box under front bed, and then 10 gauge to controller. Works well for our two trojan batteries, and they get totally charged (14v) by mid-morning if the sun is out. Rarely tilt panels.
  • Aluminum_Siding's avatar
    Aluminum_Siding
    Explorer
    Dec 09, 2015
    Ok so I'ts looking like I'll have to put the pannels on the rear of the roof. Dropping down the 10 awg that comes with the panels. From the controller to the charger (where I'll tie in the wires from the controller) will be about 3 feet. I'll be using 8 awg. The wires from the trailer's charger are 6 awg and the distance will be 25 feet so about a 2% loss. I can certainly live with that. On average 300 wt will be producing 12 amps. This is about 30-40% more than we use. We only run a small 19 inch LCD tv for 3 hours a day (kids) LED's, water pump and the furnace on low during the winter. That's about it. I picked up an extra panel when I really only needed 200 wt. The extra 100 wt is to offset not tilting the panels as well as potential amp/volt loss. I'm assuming hooking it up this way is fine. I'll have a 30 amp fuse between the panels and controller as well as the controller wire connection. Plus the trailer has all it's fuses and relays in tact. Here is a photo of the wire junctions I'll be tying into. The white and black wire are what goes up front to the battery bank. The picture doesn't do it justice. I'ts at least a 6 awg. The wires dont say but they list 600v AWM. Also it's a measurable difference in thickness than some 8 awg I compared it to. I'll post more photos off the install and finished product as I go.

  • Boon_Docker's avatar
    Boon_Docker
    Explorer III
    Dec 08, 2015
    Using a typical 100 watt 12v panel (max 18v, 6 amp) I get a different voltage drop.

    Assuming 300 watts at 18 volts and 18 amps with 14 feet of 8awg I get < 2% voltage drop.
  • westend's avatar
    westend
    Explorer
    Dec 08, 2015
    Using the voltage drop calculator linked to above, assuming typical voltages and max amperage of a parallel installation, with 8 ga. wire used (minimum connection points), I see anywhere from 3.3% to 4.75% voltage drop.

    If you wish to see half a volt or better loss, forever, from your solar installation, use the lighter wire. If you want to get the most from your panels, forever, use larger wire. This is one part of solar installation where me and Handy Bob agree, the cost of a few feet of larger wire is beneficial.

    I'd suggest, as long as you are pulling wire (and want the best for your batteries), change out that smaller wire from your converter to the batteries, also.
  • hohenwald48's avatar
    hohenwald48
    Explorer
    Dec 08, 2015
    Here's a handy voltage drop calculator.

    http://www.calculator.net/voltage-drop-calculator.html
  • Aluminum_Siding's avatar
    Aluminum_Siding
    Explorer
    Dec 08, 2015
    Thanks. I bought an extra panel for 300 total watts so I can get roughly the same amps as I would with 200 watts tilting. This way I can leave them flat and not fuss with parking east or west. This will also allow all three on the roof up front closest to my battery bank. I'll have 10 ft to the charge controller then 4 ft to the batteries. Thanks again everybody for the advice.
  • scrubjaysnest's avatar
    scrubjaysnest
    Explorer
    Dec 08, 2015
    As long as the CC has remote temp measuring and voltage sense it doesn't matter to much. Closest to the batteries is of coarse the best. The big thing is to have the cc measure the batteries temp.
  • Boon_Docker's avatar
    Boon_Docker
    Explorer III
    Dec 07, 2015
    With two 100 watt mono panels you will get approx 10 amps from the two panels on a good day. With a 20 foot run of 8awg you would have a loss of less than 2%
  • westend's avatar
    westend
    Explorer
    Dec 07, 2015
    pianotuna wrote:
    I'd run the wire directly to the batteries from the solar charge controller.

    X2
    Go with the best placement on the roof, wire up with #10 MC4 on the roof, drop directly to the controller (scheme #1) and use 4AWG from controller to batteries.

    If you are envisioning future upgrades, use a combiner box on the roof.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Dec 07, 2015
    I'd run the wire directly to the batteries from the solar charge controller.

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