RV solar DIY install Question

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  • swervn69
    Junior Member
    • Aug 2020
    • 2
    #1

    RV solar DIY install Question

    I am installing my first solar panel on my travel trailer and I have a question. It is a 250 watt mono-crystaline solar panel with an MPPT controller. Where I want to place the controller is right next to my converter. Is it okay to connect the B+ and B- out of the controller to the B+ and B- at the converter. The converter has 8 gauge wires to the battery but my solar kit came with 10 gauge wires to connect to the battery. I have a completely enclosed underbelly on my trailer and it would be about a 25 foot run to the battery from the charge controller but only about 5 ft to the converter. Would it not be more efficient to use the existing wiring from the converter to the battery and would this cause any issues with the charge controller? I know that the controller would not see the proper battery voltage if connected to the converter when the converter is charging the battery but it is only required when I am off grid so there will be no output from the converter under this situation.
    Has anyone done this and if so have you had any issues?

    Thanks,
    Tags: None
    • SunEagle
      Super Moderator
      • Oct 2012
      • 15126
      #2
      Hello swervn69 and welcome to Solar Panel Talk

      First of what is the amp output rating of that MPPT CC? That will determine the size wire between it and the battery.

      Next I will say that a CC really needs to be connected to the battery first and then the pv panels. This will help the CC determine what it is charging. If the panels are connected before the battery the CC may get confused or worse stop working.

      So to answer you, if it was my RV I would run the correct wire size (based on output amp rating) from the CC directly to the battery. Running the wire to the converter first may cause a circuit issue for your pv system and keep it from working properly.

        Comment

        • swervn69
          Junior Member
          • Aug 2020
          • 2
          #3
          Hi SunEagle,
          My MPPT CC is rated at 40 amps so this should be more than adequate for the 250 watt PV.
          I have tested the battery OCV at both the battery terminals and the converter B+ and B- terminals with the shore power disconnected and it is the same.
          They will be connected in parallel either way the only thing that will change is the length and size of the wire going to the battery will be larger and way easier to install. This way makes way more sense to me.

          solar panel connections.png

          Attached Files

            Comment

            • SunEagle
              Super Moderator
              • Oct 2012
              • 15126
              #4
              Originally posted by swervn69
              Hi SunEagle,
              My MPPT CC is rated at 40 amps so this should be more than adequate for the 250 watt PV.
              I have tested the battery OCV at both the battery terminals and the converter B+ and B- terminals with the shore power disconnected and it is the same.
              They will be connected in parallel either way the only thing that will change is the length and size of the wire going to the battery will be larger and way easier to install. This way makes way more sense to me.

              solar panel connections.png
              As much as it being a PIA the first wiring diagram is the way to go. With a 40amp output you probably need to use #8 wire between the CC and battery.

              You should also install fusing to protect the wiring between the CC and battery and battery & converter.

                Comment

                • Bala
                  Solar Fanatic
                  • Dec 2010
                  • 715
                  #5
                  You can do what you wish to as long as the numbers stack up.

                  You need to calculate the total current that can possibly travel along that cable and then calculate Voltage drop for the length. If the cable can support your total current at an acceptable Voltage drop and is correctly protected then your only consideration will be how V drop, if any, will affect your charge controller operation.

                    Comment

                    • Mike90250
                      Moderator
                      • May 2009
                      • 16020
                      #6
                      I would place the Charge Controller on it's own dedicated wire. You don't want something else to fault and disconnect the CC and leave it still connected to the panels, which is considered to generally be bad (fry) for the CC. And for convenience, having a breaker to work as a disconnect from the PV to CC is handy.
                      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

                        Comment

                        • chrisski
                          Solar Fanatic
                          • May 2020
                          • 553
                          #7
                          I don’t know the particulars of your set up, but for mine when I did the Dc voltage calculator, I was shocked at voltage loss. So, to keep cable runs short, I am going to drill a hole through the bedroom roof to keep the runs short. Drilling the hole through the roof saved about 25’ off the run I was thinking of doing through the refrigerator vent,

                          My situation is a little different with 600 watts of panels wired 3S2P, and I found that putting the combiner close to the battery significantly cut down on the size of the cable I needed to go from combiner to charge controller, and leaving room for expansion.
                          Last edited by chrisski; 08-14-2020, 04:39 PM.

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