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Old 05-11-2022, 07:59 PM   #1
Lhinkle114
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Exclamation Help with Installing MPPT

We have a 3791RD and I am installing solar in the rig. Now I don't have a lot of experience with my voltage meters, but can use the basic functions. Any advice you can give a inexperienced electrician I would appreciate it. Please be nice

Currently I am trying to install the MPPT and having problems with where my bundle of wires go after I cut the bundle under the steps. My sticking point is with identifying which black/red wires go to what. The Montana solar video says one goes to the batteries and one set go to the panels. The problem is neither set of wires show going to the the batteries, both sets go off into the underbelly. Is there any way of testing the wires to make sure I have the correct set going to the MPPT? I want to make sure I have the right set going to the right place on the MPPT before I screw something up.

Thanks for your help.
Larry
 
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Old 05-12-2022, 05:58 AM   #2
BobStack
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What year is your 3791? I believe its solar ready from the factory with a Joboni 30amp MPPT controller pre installed Including solar wiring on the roof. I would check that before you go too deep cutting wires.
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Old 05-12-2022, 07:22 AM   #3
rames14
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Larry, congratulations on going solar. First, you need to give the group a lot more info. Going on your join date, I am assuming you have solar prep. You should have a prep port in your convenience center. How many panels, which SCC are you using, lithium/AGM or LA batteries, are you adding an inverter, transfer switch? Or are you just adding a panel to charge batteries? Based on size of system, you may want to start with a clean run of wire. The original solar prep was not really set for a larger PVA. There are people here that have done everything from one panel to full systems. Best of luck.
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Old 05-12-2022, 07:56 AM   #4
Daryles
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I have installed my own system so I know where you are at.
The wiring runs from the roof gland down the wall between the bathroom and living room to the basement under the stairs. If you remove the basement wall on the right side you will see the bundle. It continues on under the basement floor and comes out in the battery compartment with a bunch of other wires. Look for a red wire with a red 30A inline fuse attached to one of your red 50A self resetting fuse.
You can verify your wiring by measuring 12vdc on the roof gland.
Regarding the pre installed solar wiring bundle under your stairs.
Cut the zip tie and separate the wiring. You will find two pairs of red and black wires along with one that looks like a phone wire. This one goes to behind your control panel inside your rig. If you pull out your control panel you will find a huge mess of wiring back there. If you plan on using this phone wire you will need to fish around in there to find it. I used this wire as a pull string to install a pull string (for future use) and a communication cable for my Victron display.
To figure out which red and black wire pairs goes to the roof and goes to the battery, you have to cut off the wire junction nut.
BE CAREFULL, the one coming from the battery is HOT 12vdc. You must disconnect the battery AND SHORE power BEFORE cutting the wires. Cut them one at a time to prevent shorts (sparks!!!) Label both pairs once you have identified them.
Install your solar panels. If I was doing mine again I would use unistrut rails. Use a stud finder to find the roof studs and painters tape to mark them. Under the mounts I put Eternabond tape down first, then drilled a pilot hole, then injected a little dicore in the hole and put a generous dab around the hole, then put the mount/rail down and install the screw, then put a dab of dicor over the screw.
Mount and connect your panels to the roof gland.
Now you can measure the voltage coming from the panels on the red and black wires in the basement.
Now mount your MPPT and connect your wires to the correct posts.
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Old 05-13-2022, 04:53 PM   #5
Lhinkle114
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Thanks for all the info, I found the red and black wires but still dont know which end goes to the batteries and which one goes to the panels. Is there anyway of testing the wires to check which one is which

Thanks
Larry
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Old 05-13-2022, 06:11 PM   #6
Daryles
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Quote:
Originally Posted by Lhinkle114 View Post
Thanks for all the info, I found the red and black wires but still dont know which end goes to the batteries and which one goes to the panels. Is there anyway of testing the wires to check which one is which

Thanks
Larry
Re-read my post above.

At this stage, you will have 2 pairs of wires, each red/black. cut the wire Crimp caps off.
Again, the wires are HOT coming from the battery.
Cut them one at a time to prevent sparks!!!
Keep the pairs separated.
Now take a multimeter and chech the voltage on the end of each pair.
The pair with 12vdc comes from the battery.
Label it " to battery"
Label the other pair "from solar panels".

To verify the pair from the battery pull the red inline 30A fuse behind the battery. Check for voltage on the wire pair. There should be no voltage.

To verify the wires going to the roof, first verify no voltage on them.
Next go up on the roof with your multimeter.
Check for voltage in your gland.
If no voltage change your meter to measure ohms.
Check for resistance. Should be infinity (open circuit).
Now go back to the basement.
Short the red/black "from solar panels" together.
Go back up on the roof
Check for resistance. Should be 0 (zero).

This verifies your wiring.
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