Wiring Multiple Solar Panels

[kmack67.km]

Hi,

I have rounded up three 100W 12V panels and a 30 Amp charge controller for my CTC. I plan to mount the panels semi-permanently on the roof and wire them in parallel to the charge controller. I have looked online for instructions and found some that suggest you need to include a diode in series with each panel, while others don't mention this. My charge controller only has one input (one +ve and one -ve terminal) for the panels so I will need to wire the parallel panel circuits to a single lead to the controller. If any of you have done this before, I would appreciate any tips or recommendations on how to connect the panels, wire gauge for each parallel loop and the main lead to the controller, good terminal connectors that would allow me to unplug individual panels if I have any need to, the need for diodes and anything else that I may not have realized yet

Best regards,
Kevin

[saltydawg]

Good quality panels should have diodes in them already, you can check this with a ohm meter. Test it with the meter on the power legs for an ohms reading, then switch the + and -. one of those should be radically higher than the other.

for 300 watts in a perfect world, you would get about 23 amps. Realistically you will get 14-18 amps out of them, if you run is under 5 to 10 feet 12 gauge would do ok, but your better off with 10 gauge. The panel leads are already probably 10 gauge.

[TimC]

+1 on Saltydawg's diode test. Some older panels may not have them. If they are lacking diodes they are dirt cheap. Your need to wire in a Schottky diode on each panel in the junction box If possible. They are less than 25 cents each. Schottky diodes will allow current through them in only one direction which helps eliminate battery bank discharging.

Search the google for "Schottky diode"

[featherliteCT1]

I noticed that Renogy and Newpowa solar panels now come with 12awg wires rather than 10awg … big change over the last year.

[saltydawg]

I noticed that Renogy and Newpowa solar panels now come with 12awg wires rather than 10awg … big change over the last year.

Well to be honest, a 100 watt panel will max at around 7 amps and 12 gauge is plenty for that. Even if you series 10 panels, its still only 7amps. The only issue is if you did a mixed parallel and series array setup and really pushed it for amps. Also the voltage drop on a 3 foot 12 vs 10 gauge wont really even be measurable difference

[featherliteCT1]

Yes, on a little teardrop short wire runs are the norm. On my trailer, each run is 30 feet round trip. So I used 10AWG for each run for each 100W panel, to achieve 2% voltage drop, per Blue Sea Circuit Wizard. I have three 100W panels.

[saltydawg]

Oh one thing none of us mentioned, if your using a mppt charger then voltage drop is a lot less of a concern. If your using a pwm charger, pay more attention to it.

[kmack67.km]

Hi everyone,

Thank you for your recommendations and info. The ohm-meter trick to check for diodes was a great hint and helped me establish that my panels already include them. Thanks also for the wire gauge recommendations. The panels come wired with a short lead that looks to be 12-guage. I will likely wire the parallel loops using 12-gauge then connect them to a 10-gauge series lead to the charge controller in the trailer. I am looking for some weatherproof, and preferably round cross-section bundled wire for the latter to make a good seal where it goes through the wire gland in the roof. I am also hoping to find some good plugs/disconnects so I can plug and unplug the panels separately if I ever need to. If any of you can recommend anything like that, please let me know.

Thanks again,
Kevin

[TimC]

Deleted previous reply suggesting Anderson Powerpoles. Sorry, I just realized you want waterproof plugs to tie your panels together.

MC4s are a good waterproof choice, however, they are a bit of a pain to take apart with or without a tool.

[featherliteCT1]

Yes, I also found those MC4 connectors hard to disconnect. However, after I put a dab of electrical grease on the rubber seals, they come a part real easy after the release tangs are squeezed.

[flboy]

Yes, on the MC4s, always pump them full of dielectric grease. Serves to protect and lubricate.

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[kmack67.km]

Thanks, for the info. Those connectors look good. Now if I could just find the three panel one in stock somewhere.

Best regards,
Kevin

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