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  1. #1
    Left The Driveway
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    2021 2500RL (first generation) pre-prepped solar wiring question

    We purchased our 2021 2500RL last August, and it came pre-wired for solar (just the wire, no solar) with a junction box on the roof with 2 MP-4 connectors in it. I moved my 2 AGM batteries to the pass-through and now I'm installing 2 Renogy 175w solar panels. The controller is a Rich Solar 40 amp MPPT mounted on the rear wall of the pass-through.

    There is a black cover mounted on that wall that has the words "SOLAR / INV LINE" printed on it. When I removed that cover there was a loop of what I think is 10AGW wire under it. What appears to be the incoming line comes out of the black plastic flex covering (on the ceiling of the pass-through) that runs from the front of the unit to the area behind the "universal docking station" cover. After removing the cover I see that the incoming line goes behind the black solar cover and loops back down the the bottom of the docking station, then goes toward the rear of the unit along with several other wires.

    After kicking this around for a while I came to the conclusion that the wire coming in was coming from the roof, then going into the unit and probably being attached to the control panel somehow, for future inverter use. That's what I was thinking until I cut that line and found it has 12v DC going through it! Help! That doesn't make any sense to me, since my mental map (I called GD CS and they had no clue what I was talking about) had that line supposed to be inert until the solar panels were connected. I thought I could cut the line, attach the incoming end to the Pv posts on my controller, and basically not use the remaining line that goes further into the unit since we are not putting in an inverter at this time.

    Can someone help me understand how to use those wires? I don't have a lot of test equipment to determine if the MP-4's on the roof are actually connected to the line I cut, or where the power in that line is coming from, etc. and I'm confused... My mental map is like Google Maps in the old days - all sorts of wrong.
    Last edited by ValKyrie; 03-03-2021 at 02:20 PM.
    2019 RAM Bighorn 6.4 Hemi
    2021 Imagine 2500RL
    Bella the chocolate Lab!

  2. #2
    Left The Driveway
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    In simple terms there should be two sets of wires connected to your controller; 2 incoming from the solar panel(s) and 2 going to the batteries. If there are no solar panels then the other wire sets must be connected to the batteries. If the voltage was DC 12.xyV, then there is either an intentional connection (which sounds premature without solar panels connected) or they were hooked up (potentially incorrectly) in error. Either way, I would trace the wires and disconnect them until they are actually needed.

    Hope you figure it out!

  3. #3
    Left The Driveway
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    UPDATE: Well, I've confirmed that the wires behind the "Solar / INV Line" cover are actually the charging leads going to the batteries from the converter! The wires for the solar panel are nowhere to be found. Waiting for GD CS to get back to me with someone who knows about solar... That should take a while. I'm bummed - got all the toys and can't install them!
    2019 RAM Bighorn 6.4 Hemi
    2021 Imagine 2500RL
    Bella the chocolate Lab!

  4. #4
    Setting Up Camp Jrparne's Avatar
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    I just installed a charge controller in the position in a 2800BH. When I took off the black plastic cap that you described I had two pairs of black and red wire. One was hot to the battery the other one was the pair that ran to the roof to the access panel to install solar on the roof.


    Sent from my iPhone using Tapatalk

  5. #5
    Left The Driveway
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    Quote Originally Posted by Jrparne View Post
    I just installed a charge controller in the position in a 2800BH. When I took off the black plastic cap that you described I had two pairs of black and red wire. One was hot to the battery the other one was the pair that ran to the roof to the access panel to install solar on the roof.


    Sent from my iPhone using Tapatalk
    Thanks! That's what I was afraid of - the second line is not there in my unit. I'm going to see if I can get confirmation from GD that it was supposed to be; if not, that's taken the project up a notch.
    2019 RAM Bighorn 6.4 Hemi
    2021 Imagine 2500RL
    Bella the chocolate Lab!

  6. #6
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    Here's what you are looking for on the roof (pic from roof side of housing): https://www.mygrandrv.com/forum/asse...8&d=1615874587 There is a cap over the connectors that is sealed up. Wires from pass through to connector on roof. Wires from pass through to batteries.


    Yeah, I was skeptical when I asked my dealer to ohm out the solar wires for me, in case someone at the factory had had a rough weekend, and they said they jumpered the roof port, then removed the end at the battery and measured continuity and resistance. Numbers looked right, so I went with it. My plan is to use two Jackery 1000 units to power in the rare instance I need to boondock. One can charge (even in motion) with panels on the roof, while the second is being used. Took me a few beats to realize I could run the main shore power cable up through the port for the water line and use a TT-30 to 110V adapter to plug into the Jackery and run everything except maybe the AC (need to test that. I'm pretty sure I can run it once started, but with only 2000W surge power, doubt I can get it started).


    I had wanted a way to plug the Jackery in inside the pass through, but running the cable outside is fine. I think you can do the same thing by putting a charge controller with inverter between the solar panels and battery, with the output from the charge controller/inverter running the trailer with the help of the batteries when demand is high and charging the batteries when demand is low. Not sure how much that costs, though. As a bonus, the Jackery has a 12V output, so you can charge your batteries with it, too. There is a little inefficiency and you can't charge one Jackery from solar while maintaining a 12V output to the batteries, but there is an MPPT charge controller built in. I might add a tiny standalone charge controller as a battery tender, but I like the flexibility of fully portable power. Leave one in the trailer, charging off the roof panels, and maybe plug in a couple portable panels if you need a little more oomph, and take the other one with you for who knows what.
    Last edited by dbphillips; 03-16-2021 at 12:08 AM.

  7. #7
    Left The Driveway
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    UPDATE 2: I cut the wire, and sure enough, one side goes to the MC-4 connectors on the roof, the other end has 12 volts of power, charging the batteries when on shore power. This makes no sense to me, since that means before I cut the wire the MC-4's were receiving 12 volts from the batteries! I get that I am supposed to connect the line that comes down from the roof to the the MPPT controller, but how do I connect the battery charging circuit so that the batteries will charge on shore power? Running a new line back to the auto-reset breaker would just complete that power circuit again, pushing voltage to the solar panels. I know I'm missing something here...
    2019 RAM Bighorn 6.4 Hemi
    2021 Imagine 2500RL
    Bella the chocolate Lab!

  8. #8
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    Quote Originally Posted by ValKyrie View Post
    UPDATE 2: I cut the wire, and sure enough, one side goes to the MC-4 connectors on the roof, the other end has 12 volts of power, charging the batteries when on shore power. This makes no sense to me, since that means before I cut the wire the MC-4's were receiving 12 volts from the batteries! I get that I am supposed to connect the line that comes down from the roof to the the MPPT controller, but how do I connect the battery charging circuit so that the batteries will charge on shore power? Running a new line back to the auto-reset breaker would just complete that power circuit again, pushing voltage to the solar panels. I know I'm missing something here...
    Yeah, they really should put a lug strip in the pass through to tie those off to, rather than tying them together. But if you are plugging solar panels in on the roof before you know what's on the other end, you shouldn't be touching it.

    So, if you just disconnect the batteries from the solar port, I'm pretty sure you will find they are still connected to the trailer and will charge from shore power. Where you may want to ask GD what to do is when you reconnect the batteries to your charge controller. I'm not sure what happens when the charge controller and the shore power are both charging the batteries. Seems you would want the 12V charge from the trailer to go through the charge controller, too, so it can manage it all. As I mentioned, my use profile is different, so haven't researched that.

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