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.

I have three 100s in parallel with PWM, and can get about 18.6 amps to the battery with a high sun on the array. I use #8. Can't say if #10 would be as good.The main thing is that with PWM, your line loss is not very important. You will still get your 18 amps. BUT if you have MPPT then it is important, because the amps to the battery you get works differently from with PWM. MPPT amps is all about watts from the controller divided by battery voltage. Line loss reduces wattage.

I had to go look at what PWM and MPPT where again. 4 years ago when I first did this I studied up an knew a thing or two but have since forgot much of the info. The system worked and kept my battery's charged very well so I didn't have to think about it.I am using a PWN 30 amp controller. The Windy Nation P30L model.

Another question.I see I can get a 3 way MC4 connector, are all MC4 connectors the same? If I purchase a 3 way will my existing connectors of another brand hook up right? Or will I have fit issues between brands? My current MC4 connectors are from Windy Nation, they don't have a 3 way and to hook up 3 panels using there system looks like just to many connections to fail.Just wondering if I decide to take the easy way and just replace MC4 connectors instead of doing a combiner box. I have a bag of extra MC4's around someplace.

10 gauge wire is a little small for such a long run. I used 8 gauge for about a 10' run on mine from the combiner box down to the controller. If they are truly MC4 connectors, you should be able to interconnect between brands.

Two good sources of large wire are genuinedealz.com for boat wire or Temco on eBay for welding wire. The boat wire is tinned so it's more expensive.

Solar wiring question | Good Sam Community

24 Replies

pauldub
Explorer
Mar 08, 2019
10 gauge wire is a little small for such a long run. I used 8 gauge for about a 10' run on mine from the combiner box down to the controller. If they are truly MC4 connectors, you should be able to interconnect between brands.
Muddydogs
Explorer
Mar 08, 2019
Another question.
I see I can get a 3 way MC4 connector, are all MC4 connectors the same? If I purchase a 3 way will my existing connectors of another brand hook up right? Or will I have fit issues between brands?

My current MC4 connectors are from Windy Nation, they don't have a 3 way and to hook up 3 panels using there system looks like just to many connections to fail.

Just wondering if I decide to take the easy way and just replace MC4 connectors instead of doing a combiner box. I have a bag of extra MC4's around someplace.
Muddydogs
Explorer
Mar 08, 2019
I had to go look at what PWM and MPPT where again. 4 years ago when I first did this I studied up an knew a thing or two but have since forgot much of the info. The system worked and kept my battery's charged very well so I didn't have to think about it.

I am using a PWN 30 amp controller. The Windy Nation P30L model.
BFL13
Explorer II
Mar 08, 2019
I have three 100s in parallel with PWM, and can get about 18.6 amps to the battery with a high sun on the array. I use #8. Can't say if #10 would be as good.

The main thing is that with PWM, your line loss is not very important. You will still get your 18 amps.

BUT if you have MPPT then it is important, because the amps to the battery you get works differently from with PWM. MPPT amps is all about watts from the controller divided by battery voltage. Line loss reduces wattage.

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Solar wiring question

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