Hi All - I currently have 2 12 volt 165 watt panels wired in series on the front part of the roof on our small 5th wheel camper. I have a 3rd panel with the same specs I'd like to install when the weather get's better here in Michigan, but I'm unsure of the best way to install it. The only available real estate for the 3rd panel is at the rear of the camper. I can envision scenario's where the rear will be in shade, but the front is not, and vice versa. I have a 40 amp MPPT controller, and I believe with only 3 panels I HAVE to wire in series, or change them all to parallel, but that would entail replacing existing wiring, and thicker wiring, 8 or 6 gauge rather than the 10 gauge I have now. My thought was maybe I could put in some sort of 3 way switch so that all panels would be connected, or just the front, or just the rear. Does that make sense, and if so, can anyone recommend a switch to accomplish it?

Before the switch thing, I'd check the panel specs for bypass diodes. It isn't always a death sentence for series panels.I'm a big fan of series and would like to have you stick with that. I'd go the switch route rather than change to parallel.

We need to know Voc info.Voc per panel?Voc of MPPT?HTH;John

2oldman wrote:Before the switch thing, I'd check the panel specs for bypass diodes. It isn't always a death sentence for series panels.I'm a big fan of series and would like to have you stick with that. I'd go the switch route rather than change to parallel.All 3 panels are the same specs, with bypass diodes, and the 2 front so far have seemed to be fairly immune to intermittent shading. Not sure how they will be if one whole panel is completely shaded.

GaryS1953 wrote: Not sure how they will be if one whole panel is completely shaded.You could blanket one of your 2 panels and see how it reacts.

The videos I've seen and reading led me to install my three panels (front mounted) in parallel. Tito's was one of them. Not that much difference series vs. parallel. But I do plan to install one more in the back via 10 gauge to the combiner box. I too felt the back end of my TT would be shaded more than the front. 165 watt panels in parallel should give you plenty of volts for the controller to "shave off" and stuff the batteries.

Adding 3rd Solar Panel | Good Sam Community

Almot
Explorer III
Feb 12, 2018
Wire them in series with existing #10 cable and see if shaded panel bothers you too much.
You have nothing to lose, just a short piece of MC4 extension cable, $10 worth.
You only need big amps until it goes into Absorb stage.
Lwiddis
Explorer II
Feb 13, 2018
“You only need big amps until it goes into Absorb stage.”

Yes, Almot. A fact not understood by many RVers.
Lwiddis
Explorer II
Feb 13, 2018
Almot, recommending #10 wire other than from one panel directly to a controller or to a combiner box just isn’t right.
mike-s
Explorer
Feb 13, 2018
The bypass rectifiers (a diode is a vacuum tube, why are they still called diodes - we don't call transistors triodes?) will take care of any shading issues, with only very minor power loss. Just wire them in series and don't worry, be happy.
full_mosey
Explorer
Feb 13, 2018
GaryS1953 wrote:
2oldman wrote:
GaryS1953 wrote:
Controller is a 40 AMP Renogy Tracer MPPT.
According to what I find, that controller should be good to near 100v.

Yeah,I knew the controller was adequate, just trying to prevent possible shading problems by maybe finding a way to isolate shaded panels.

You only guessed! 12V panels are usually below 24Voc. Three panels in series is less than 72Voc.

The MPPT will be good to go in series.

I have 12V panels in parallel on my TT and in series on the van.

HTH;
John
CA_Traveler
Explorer III
Feb 13, 2018
Series will be the most shade tolerant, due to the bypass diodes. Installation is a slam dunk since you just add the third panel to the other two.

Recommend you run the Morningstar String Calculator to make sure of your VOC at your low Michigan temps. But I suspect you'll be OK.

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