Solar wiring question

[Muddydogs]

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.

[pianotuna]

I used twin #12 (i.e. four wires) from the panels to a combiner box (home brew). Then the #10 prewire to the controller. #8 from controller to battery bank. I went MPPT so input is 33 volts. Output is 17 amps at solar noon if the batteries are hungry.

[Muddydogs]

Found a good price on 8ga wire so I can go that route. I'll have to do some measuring because I just don't remember but looking at my order from a few years ago when I purchased the system it came with 40 feet of 12ga and I added another 50 feet. I cut the 90 feet in half and ran the lines off the roof and I remember I did have some waste when I got to the charge controller but not sure how much. But I'm all of 40 feet and probable a little move. Panels are at the rear of a 28 foot toy hauler thats all of 10 foot tall at the center fridge vent. I did extend the panel pigtails out a ways, probably had 3 foot of pigtail per panel.

My reasoning for getting rid of the MC4 connectors is there out in the weather all year, buried under snow all winter and when they did fail it was a pain getting on the roof. I got the smallest guy in camp, backed the pickup up to the trailer, set a camp table on the tailgate then two of us boosted the guy from the table to the trailer roof. This was the second day of a 10 day hunt so I ended up running the genny way more then usual to keep the batteries up because the solar just wasn't doing good even after the guy fiddled with the connections. So I figure a weatherproof box with the cables in a bus or ground bar will be better then the MC4's.

[red31]

I'd limit voltage drop to 1v (PWM) and I'd use 5.0A for each 100w.

This should keep ya on the constant current side of the IV curve most of the time, left of the knee.

30', 12g, 10A ~1v this is 1v/12v = 8%, 1v/16v = 6%
30', 10g, 16A ~1v

[BFL13]

Ed_Gee wrote:

BFL13 wrote:

Ed_Gee wrote:
Since I did not see any previous comment on this, I thought I would point out that voltage loss on 30 feet of 12AWG is approximately 9%.....pretty high. Most professionals I have dealt with don't want to exceed 3% loss.

Is that at 20 amps?

Since the Original Poster was contemplating 300W, I used 18A which is about all that 300W would provide in full sunlight. Regardless the current, though, 9% loss at any rate is unacceptable.

Not sure 9% would matter with PWM, which he has. Have to do some math. Thing being, PWM means array voltage is battery voltage , much lower than panel voltage, so you can afford some voltage drop panel to controller. Not with MPPT though.

See earlier post on which voltage drop calculator and whether round trip or one way to do the calculation.

You are correct to raise the voltage drop issue.

[Ed_Gee]

BFL13 wrote:

Ed_Gee wrote:
Since I did not see any previous comment on this, I thought I would point out that voltage loss on 30 feet of 12AWG is approximately 9%.....pretty high. Most professionals I have dealt with don't want to exceed 3% loss.

Is that at 20 amps?

Since the Original Poster was contemplating 300W, I used 18A which is about all that 300W would provide in full sunlight. Regardless the current, though, 9% loss at any rate is unacceptable.

[naturist]

I agree, 12 guage wire is too small for a 30 foot run. I’d go with 8. That is a long run for 12, so your losses will be high. The wire size chart I use says 20 amps or less, at 12 volts, you can use 12 guage only up to 13 feet. Up to 22 feet, use 10 guage, and although you are mostly higher voltage, the longer run needs 8 guage.

[BFL13]

Ed_Gee wrote:
Since I did not see any previous comment on this, I thought I would point out that voltage loss on 30 feet of 12AWG is approximately 9%.....pretty high. Most professionals I have dealt with don't want to exceed 3% loss.

It is worse using this calculator. I wonder if that one was for the round trip or just one way. This one gets 14.x% using #12 and 5.x% using #8 copper at 30 ft distance (a "set", so round trip) at 20 amps at 13v DC (unless I messed up of course!)

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=2.061&voltage=13&ph...

[Almot]

Have found the company that I bought #10 MC4 extension from - Unlimited Solar. Quality stuff. They sell through Amazon, Ebay and directly from their website.

Here is copper MC4 #8:Copper MC4 #8. You need 50ft to make 2 leads 25ft each. Check your exact length and run the numbers - maybe #10 will work, - they have it too. Clickable text feature doesn't seem to work.

I would not worry (too much) about material of short pigtails #12 on panels, in this particular setup.

[BFL13]

Ed_Gee wrote:
Since I did not see any previous comment on this, I thought I would point out that voltage loss on 30 feet of 12AWG is approximately 9%.....pretty high. Most professionals I have dealt with don't want to exceed 3% loss.

Is that at 20 amps?

[Ed_Gee]

Since I did not see any previous comment on this, I thought I would point out that voltage loss on 30 feet of 12AWG is approximately 9%.....pretty high. Most professionals I have dealt with don't want to exceed 3% loss.

[BFL13]

pauldub wrote:

BFL13 wrote:
The pigtails on these are aluminum. I found that out when cutting mine short. Of course, I cannot verify that other brands do the same thing for their pigtails.

Good to know you can get the long wire that is copper.

http://www.wegosolar.com/products.php?product=Canadian-Solar-255-watt-Solar-Panel-BLACK-Frame-

Note in that link they have the electrical data for the mono version, so ignore that. They have the poly version (I now have two of them)

Is it possible that the wire is tinned copper? Some of the pre-made solar cables that I've purchased have tinned copper and it can look like aluminum if you don't look at the cut end.

EDIT--I worked away at it some more and in better light it does appear to be copper under the tin. Good to learn that, thanks.

I have a piece of it so I was able to check just now. Scraped the strands with a knife and they just got shinier.

The cable info says:

(UL)E310273 RHH OR RHW-2 / E305787 PV WIRE 12AWG 90C WET OR DRY 600V
SUN RES -40C >> H + S 12583780-769871 RADOX SMART << TUV.COM ID:
0811307400 PV1-F 4MM2 120C 0.6/1 KV

Whatever that all means! 🙂

[pauldub]

BFL13 wrote:
The pigtails on these are aluminum. I found that out when cutting mine short. Of course, I cannot verify that other brands do the same thing for their pigtails.

Good to know you can get the long wire that is copper.

http://www.wegosolar.com/products.php?product=Canadian-Solar-255-watt-Solar-Panel-BLACK-Frame-

Note in that link they have the electrical data for the mono version, so ignore that. They have the poly version (I now have two of them)

Is it possible that the wire is tinned copper? Some of the pre-made solar cables that I've purchased have tinned copper and it can look like aluminum if you don't look at the cut end.

[BFL13]

EDIT- scraped the strands and it turns out to be tinned copper, so not aluminum.
----------
The pigtails on these are aluminum. I found that out when cutting mine short. Of course, I cannot verify that other brands do the same thing for their pigtails.

Good to know you can get the long wire that is copper.

http://www.wegosolar.com/products.php?product=Canadian-Solar-255-watt-Solar-Panel-BLACK-Frame-

Note in that link they have the electrical data for the mono version, so ignore that. They have the poly version (I now have two of them)

[Almot]

Muddydogs wrote:

I see I can get a 3 way MC4 connector, are all MC4 connectors the same?

No, they are not - not in terms of quality.
MC4 is actually a brand, though many suppliers use this term for knock-offs of the same configuration. Buy from reliable sources. I forgot the name of mine - plenty of #10 and #8 MC4 cables, all copper, all US made. Genuinedealz is a good place too, I bought custom length battery cables from them.

Wire #12 is rather odd, for this install. Panel pigtails are #12, but for MC4 extension cable most people use #10 (at least). There are also MC4 #8 cables available. I tried to run the Southwire V-drop calculator, but their newly (yesterday?) redesigned interface is missing the "Calculate" button :). No kidding. Hopefully they will fix this.

Plastic and o-rings don't last forever. Hide the panel pigtails with MC4 under the panel, leave only the cable exposed.