Solar wiring question

Muddydogs wrote:
Currently I have 2 100 watt panels on top of the trailer (VOC 21.6 volts, ISC 6.34 amps, VPM 17.4 volts, IMP 5.75 amps) with a 30 foot run of 12ga wire to the charge controller.

Last fall my system stopped charging and upon inspection one or more of the MC4 connectors are not making a good connection. My plan is to remove the MC4 connectors and make a water proof bus bar box on the roof to connect the panels to the main line.

I was thinking when I was up there that I should install a third panel. From what I can tell if I'm running the numbers right the 12ga wire will safety handle the max output from 3 panels but my line lose is high. If I switch the 30 foot of main line to the controller to 10 ga am I really gaining a lot with line loss? Will I be getting anything extra by adding a 3rd panel?

Looking at a wire table it appears that even going to 4ga wire won't get me down to a 2% loss for my run length.

What I would do:

It is definitely worth adding a 3rd panel if you want one. I would not change the 12g wire. Your voltage loss won't be enough to worry about, and that 3rd panel will still be well worth it.

I would not replace the MC4 connectors until I had tried to save them. Probably just the act of disconnecting and reconnecting has cleaned up whatever corrosion you had. Work on cleaning the pins a little more, use some DE grease, and reassemble. If you can't get them cleaned up well enough to suit yourself, just replace them with new connectors (don't eliminate them).

If you feel corrosion would be an ongoing problem (an indication would be that you had more than one connector failed), you could use heat shrink tubing with an adhesive lining and shrink it over the entire connector. This stuff is available in large diameters and is used for battery cables and the like. Amazon has it. Just be aware that it is good stuff, and if you ever need to remove it, it is a job to get off.