Solar and 12 AWG wiring

[radarcontact]

After giving FWC my serial # on my Hawk, I was assured by FWC that my wiring was 10 AWG from the factory, but my inspection of most of the wiring behind the solar controller looks to be 12 AWG. There is some 10 AWG going to the battery, but it has some 12 AWG spliced on to the last foot, where the loop connector to the battery is....confusing. What's more, they put 30A fuses in-line on the connections coming into the controller, and to the battery. Still waiting to hear their response to my last email.

I've replaced the 30A fuses w/20A for my own personal safety reasons. If I hook up 2 or 3 12V solar panels in parallel, how many amps could I run through those 12 gauge wires? Up to 20 amps? I know if the runs are long there could be heat buildup in the wiring, but I don't think our campers have excessively long runs...maybe I'm wrong. Also, the panels I'm considering have a max output of 17.8A in total (i.e., summing up all parallel circuits) - that would be under ideal conditions. My connections would probably be two panels connected w/a Y connector into the same rooftop plug, and possibly a third portable panel on the secondary outer wall plug. The rooftop plug could potentially have up to about 13.3A under max conditions, the sidewall plug 4.5A under max. I could rework this so that the rooftop plug would have about 9A max and the sidewall plug about 9A max...maybe that would be better to evenly distribute the inbound current between the two connections. Normal output under partly cloudy skies would probably be in the order of 10-14A total.

Any thoughts/opinions would be appreciated.

 

[Vic Harder]

There are a variety of wire size and "ampacity" guidelines out there. Here is one - https://www.powerstream.com/Wire_Size.htm

20A fuse on 12 gauge sounds reasonable. That chart lists max current as 41A for chassis wiring. It doesn't give a continuous rating.

Run from front (nearest truck cab) end of camper to roof is about 15'.

Why connect the roof panels in parallel? If you have an MPPT controller, it will give you better results/power if you go serial. Less power loss, more room for the controller to convert input power/currents to what the battery needs at the moment.

If you are looking at doing both the roof and rear wall plug at the same time, I can see the desire for parallel connectors. Makes it easier to use just one PWM controller.

If you are putting two of these on the roof
https://www.renogy.com/renogy-160-watt-12-volt-polycrystalline-solar-panel/
then you could see close to 20A under ideal conditions from the panels in parallel. Using the calculator on that page I linked, you are looking at 8% voltage drop. NO BIG DEAL, as you will be usually be putting out way more (optimum voltage is listed as 18.6). Your PWM will see 92% of that under ideal conditions = 17v or so.

BUT, because the batteries will only want 14.8 or so max (absorb voltage for my batteries) the controller will toss away (17-14.8) = 2.2V.... under ideal conditions only! Usually your panels won't be producing that much voltage, so the "toss away" power is less.

In any case, 12 is ok for 20A. PWM controllers will work, and are nice if want to use both the rooftop and back/portable connection at the same time.

MPPT is "better" and the power losses are less, and the "toss away" doesn't happen, so you get more power out of them. But you would need two (or do some real fancy wiring) if you want to use both portable and roof solar.

I better stop.... feels like I am rambling and going too deep.

 

[radarcontact]

Thanks for your reply, Vic. I'm still getting my head wrapped around this....I checked the specs for my MPPT controller. Says it can accept a max voltage of 50V. Recommended max is ~40V. I know if you connect panels in series voltage is additive, but amperage is not.

Let's forget about a portable panel for a minute. I currently have a 160W and a 80W on my roof. I can add another 80W on the roof and increase the weight on the roof by no more than 14 lbs, so if I did that, what is the advantage of wiring that stuff in series? Max amps for the 160W is about 9A, and for each of the 80W panels about half that, or 4.5. Voltage would be all three added together, but wouldn't the amperage be maxed out at the lowest common demoninator, i.e., 4.5A? Why is this better than adding amps as in parallel? I know that increasing voltage lowers the current, but why is that advantageous, other than allowing you to use smaller gauge wire? Won't it take a lot longer to recharge the batteries with lower amperage?

Since these 3 panels are operating at 17.5-18V, not sure if I could wire them in series - total volts at max could exceed 50V. Don't think I can wire the two 80w in series and then connect the 160w in parallel...voltages would be different. I think my only option is to wire it all in parallel. BTW, I couldn't do what you suggested, i.e., two 160W panels, because I have 2 air vents on my roof, and not enough space for the width of a second, wide 160W panel. Two skinny 80s works good in addition to the 160 I have.

 

[rando]

If you were to add a second 80w panel, in addition to your 160W panel, you could put the two 80W panels in parallel (V = 18V, I = 9A), then put this combination in series with your 160W panel for a combined V = 36V, I = 9A. The MPPT takes care of converting what ever combination of current and voltage it gets at the input to the correct charge voltage at the output, conserving the power (watts in = watts out). To the first order it doesn't matter to the charge controller if you connect the panels in series or parallel.

The one draw back to series, is you then can't use a portable panel through the same controller, as it would be in parallel and the voltage would be too low.

 

[Vic Harder]

+1 to what rando said!

 

[radarcontact]

Thanks for your reply. I'll have to use more expensive Zamp 80W panels, as they have the footprint I need for my rooftop configuration. Fortunately they're fairly light. I have this connector:
https://backcountrysolar.com/collections/mounting-options-and-accessories/products/parallel-solar-panel-y-connector

It allows two Zamps to hook up to the same port/plug. When I look at the specs I can't figure out what's going on w/the Y connector. Amperage is added, so is it a parallel connector? It says it is in the title, and that it can handle up to 200W safely. Looks like heavy gauge wire. Say I connect both 80s to this plug and to port #1 on my camper. If I connect the 160W to port #2, could I wire the 160W and the two 80W panels in series BEHIND the controller, where the connections all come together in the push connectors? I have to rewire everything in series...I'll make a diagram and post it.

 

[radarcontact]

Rando and/or Vic, here's a lousy diagram of my setup in series as you guys suggested:




Just not sure about the Y connector, but I think it accomplishes the parallel connection between the two 80W panels.

Thanks for your help.

 

[Vic Harder]

Rando and/or Vic, here's a lousy diagram of my setup in series as you guys suggested:

Wiringdiagram.jpg

Just not sure about the Y connector, but I think it accomplishes the parallel connection between the two 80W panels.

Thanks for your help.

That would do what rando suggested.... 2x 80w in parallel, then those in series with the 160w. What's the dohicky you are using in the middle to join them in series? Where are you going to locate that? Close to the controller, I imagine.

Possibly related, what do you mean in the post before this one, when you say "two 80W panels in series BEHIND the controller, where the connections all come together in the push connectors?" Behind how? Physically? Logically? Both?

 

[camelracer]

I have read that a parallel connection is more efficient if either panel is partially shaded.

 

[radarcontact]

The dohicky is just a 3-hole wire push connector, looks like this:


That would do what rando suggested.... 2x 80w in parallel, then those in series with the 160w. What's the dohicky you are using in the middle to join them in series? Where are you going to locate that? Close to the controller, I imagine.

Possibly related, what do you mean in the post before this one, when you say "two 80W panels in series BEHIND the controller, where the connections all come together in the push connectors?" Behind how? Physically? Logically? Both?




It can accommodate up to 10 AWG wire. I have about a dozen of these not being used so I'll probably use them for the connections.

It will be right behind the controller, where all the wires come together. And, yes to your second point....physically behind the controller.

I understand how wiring this way allows more voltage, less current, which means long wire runs can happen w/smaller gauge. Are there any other benefits wiring in series w/the MPPT vs. parallel? I've read some data online about this, but most of it says that it's more 'efficient' to wire in series w/MPPT, that more solar energy is captured and transmitted to the controller - not sure why that is. Someone else made the point that wiring this way can be detrimental when the sun is not out fully, or you're in shade, because one shaded/low voltage panel can draw the rest of the panels down.

 

[rando]

I am not sure I understand how you are going to wire this. If all these panels are going on the roof, how will you use the side wall connector?

 

[radarcontact]

I am not sure I understand how you are going to wire this. If all these panels are going on the roof, how will you use the side wall connector?

The sidewall connector is identical to my rooftop plug. My 160W panel will plug in there. The connections meet behind the MPPT controller now....all I have to do is rewire in series what's back there. It's wired in parallel at the moment (i.e., the rooftop and sidewall plugs), but the sidewall plug is currently not in use. When all 3 are hooked up, the two 80s will connect through the rooftop plug, the 160 through the sidewall, and then in series behind the controller in the camper.

Here's the way the wires look now behind the controller. I will have to do some rewiring, but I can do the series wiring back here:

 

[rando]

Won't you then have to have a cable stretching down from the roof to the sidewall, including enough slack so you can raise the roof? To me, that doesn't seem like an elegant or reliable solution.

Why not just wire all the panels through the roof plug?

 

[radarcontact]

Won't you then have to have a cable stretching down from the roof to the sidewall, including enough slack so you can raise the roof? To me, that doesn't seem like an elegant or reliable solution.

Why not just wire all the panels through the roof plug?

I've thought about that, but the 160W panel is between the two 80s. I think that's going to require a lot of wires running back and forth across the rooftop w/the parallel and series connections, but maybe I'm wrong. Also seems a little confusing to me how to do SAE connections with series wiring. If everything goes through the same receptacle, I'd have to split the positive and negative wires up somehow, and then they come back together at the rooftop receptacle...? LOL my head is going to explode . I agree w/you though, if I could get it all through the rooftop plug it would be more elegant.

 

[radarcontact]

Rando, I drew this out on paper. I can still use my Y connector for the parallel connection between the two 80s, but I'll need to cut and solder for the series connection to the rooftop plug. Would you concur?

 

[rando]

I don't think the roof wiring would be that bad. Assuming you are installing the 160W panel over the roof plug (between the vents), you can just run all the wires to near the roof plug, then make a little parallel/series adapter there out of SAE pigtail connectors. You can secure this harness to the back of the 160W panel, out of sight and out of the weather.

Or you could put all the panels in parallel using this guy:
https://www.amazon.com/Sunway-Solar-Connector-Extension-Expanding/dp/B0758G9YPK

And be done.

 

[rando]

You would need to make your own series connector if you want to go the series/parallel route, but you could use WAGO push to connect blocks if you are not comfortable soldering. If you secure it under the 160W panel, it is out of the weather.

Also are you sure you need 340W of solar on the roof? I previously had 240W of solar on the roof, and this was more than enough to sit in one place indefinitely in my Fleet. I now have a 160W on the roof and a 100W portable (which I rarely use), which is also plenty of power here in the sunny rockies.

 

[radarcontact]

If I wanted to go back to parallel connections only I don't think I could use that connector....it's 18AWG and wouldn't support 18A total between the three panels.

I see what you're saying regarding the pigtails. Thanks for giving me a visual image.

I've been using my camper more and more off-season, when the sun is not as prevalent, so I've been thinking I may like some more PV input than 240W. We've also been running more gadgets off camper power. It may be overkill at times, but l think I'm on the right track. The 160W panel I've had isn't cutting it, I can't fully recharge my 230ah batteries when I'm off the grid for a few days. I haven't tried the 240W setup I currently have in fall weather/low light, so you may be right about it being enough.

 

[rando]

We primarily use our camper in the shoulder and winter season as well - and this is where a portable panel really shines ( ). Sun angles are really low, so the flat mounted panels are only producing ~50% of their rated output. However, you can angle the portable to match the sun angle, meaning it gets much closer to it's rated output. Given your situation, it may be a good idea to wire the 240W of panels you have on the roof in parallel, then get a third 80W panel to use as a portable (connected to the wall plug, and therefor in parallel with the other panels) and see how it goes. You could always roof mount it later if that is the option you decide on. All you would need is the ZAMP 2-1 adapter you posted earlier.

 

[radarcontact]

We primarily use our camper in the shoulder and winter season as well - and this is where a portable panel really shines ( ). Sun angles are really low, so the flat mounted panels are only producing ~50% of their rated output. However, you can angle the portable to match the sun angle, meaning it gets much closer to it's rated output. Given your situation, it may be a good idea to wire the 240W of panels you have on the roof in parallel, then get a third 80W panel to use as a portable (connected to the wall plug, and therefor in parallel with the other panels) and see how it goes. You could always roof mount it later if that is the option you decide on. All you would need is the ZAMP 2-1 adapter you posted earlier.

My thinking also. Getting a small portable is a lot less work. Just as an exercise, I made a diagram of what I'd have to do to connect all panels in series thru the rooftop....it wouldn't be hard to do. Thanks for giving me the starting point. I could use these 3 pigtails and do it fairly easily w/Waco connectors:

https://www.amazon.com/WGCD-Heavy-Automotive-Extension-Waterproof/dp/B07C8CK5DS/ref=sr_1_fkmr3_1?ie=UTF8&qid=1534521998&sr=8-1-fkmr3&keywords=SAE+pigtail+14+AWG+12%22


I do have one question.....if I were to go w/3 panels on the roof in series, what becomes of the sidewall plug that's wired in parallel to my roof plug behind the solar controller? Obviously wouldn't need it, but would it have to be disconnected from that parallel connection? Or could I just ignore it?