Looking for Technical Feedback on RV Solar Installation

I’d like to get some technical feedback on a solar system that was recently installed on my RV, which is a 26’ Travel Trailer. I’d like to make sure that I’m taking full advantage of solar this coming fall, when the sun angle dips low up here in the north country. But I’m not sure that my system is wired correctly to take full advantage.

My system now has two Interstate 6-volt deep cycle batteries wired in a series which yields about 225 amps at 12-volts. The batteries are mounted on the front tongue behind the propane tanks.

There are four solar panels mounted on the roof at the front of the trailer above the batteries. The solar panels are each 100 watts, 18.9-volt, 5.29 amps per panel for a total of 400 watts. The two solar panels on the left are wired in a series – as are the two solar panels on the right. Then the left and right series panels are wired [10 gauge wire] in parallel to the combiner box on the roof. The two positive and negative solar wires [10 gauge] from the combiner box go through the roof to inside the camper closet to a fuse and then down to the solar controller, which is a Morningstar’s ProStar 30 amp PWM with meter model mounted along the wall. The wires [4 gauge] go down into the storage compartment, where there is another in-line fuse and a shut-off switch. Then over to the batteries for about the shortest run possible for a travel trailer with a seven foot ceiling.

So far, I’ve been using the system for a couple of weeks [August in the U.P.] and it seems to be working well. The batteries are charging up fully each day. The highest reading I’m getting on the solar controller meter when the sun is high has been 7 solar amps. Mid to late morning, it’s around 4 amps.

I have three basic questions:

1. From what I’ve been reading in a certain forum, my 30 amp PWM controller is not the right fit for what I’ve got installed and I should have the solar panels all rewired in parallel to the combiner box. If that’s the case, why is my PWM controller not adequate?

2. And, what size wiring would you recommend from the combiner box to the controller?

3. My installer did not use all of the in-line fuses that I purchased for the job. Should I have a fuse on each panel?


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking for Technical Feedback on RV Solar Installation

    Welcome to the forum.

    Yep; it's wired wrong.

    Putting two panels in series = double the Voltage. The PWM type controller can not make use of this 'extra' Voltage for charging your 12 Volt system, so in essence half your panels are doing nothing.

    You should have all four panels in parallel to the combiner box with a fuse on each one. That will give you the full 20+ Amps potential of all panels, which is right for your battery size.

    10 AWG from the combiner to the controller should be able to handle the full current with minimal Voltage drop at up to about 10' of distance.

    If you can fix it so all the panels are in parallel at the combiner and each has its own fuse you should be good.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Looking for Technical Feedback on RV Solar Installation

    or replace the PWM CC with an MPPT one. Cost of hiring someone to rewire vs cost of a new CC. Can/will the vendor take a return?
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  • vsheetzvsheetz Registered Users Posts: 18 ✭✭
    Re: Looking for Technical Feedback on RV Solar Installation

    Wiring them all in parallel with provide additional shading mitigation.
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