Solar Panel Wiring Choices - Fiberglass RV


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Old 05-13-2013, 09:13 PM   #1
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First and foremost, thanks to this wonderful community, 90 watts of solar (2x45W) panels just arrived from solar blvd. BTW, it's worth calling them to order. They added a 20A charge controller plus LCD volt/amp display for $55 and reduced shipping from the website quotes. Plus the panels were $1/watt. Great deal, I think.

Now I want to put them up on the roof of my 1991 Scamp 16, and was thinking of running the cables in from the roof vent, at least for now. I want a way to have the charge controller inside and I don't want to drill holes in my new-to-me egg yet.

My question: can I connect the charge controller's OUTPUT anywhere that sees 12v? For example, can I tie it into the wire nuts in the cabinet over the stove? It's a 15A fuse in the power converter fuse box so I shouldn't be past half of that at 12-14V, even at peak sun.

That'd be most convenient for access. Easy to connect and disconnect. It's probably temporary until I figure out all the little storage places, and then drill holes and probably mount it permanently by the voltmeter by the door.

I realize I may lose a bit of power getting to the battery along longer internal wires. I'm fine with that for now. Other than that, any concerns? Am I about to scramble my egg?

Thanks for this new obsession!
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Old 05-14-2013, 07:55 AM   #2
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Originally Posted by Ken in Philly View Post
First and foremost, thanks to this wonderful community, 90 watts of solar (2x45W) panels just arrived from solar blvd. BTW, it's worth calling them to order. They added a 20A charge controller plus LCD volt/amp display for $55 and reduced shipping from the website quotes. Plus the panels were $1/watt. Great deal, I think.
Thanks for the tips. I wouldn't have thought to call them.

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Now I want to put them up on the roof of my 1991 Scamp 16, and was thinking of running the cables in from the roof vent, at least for now. I want a way to have the charge controller inside and I don't want to drill holes in my new-to-me egg yet.
I understand your hesitation. They do make some nice waterproof pass through fittings, I believe for marine use.
http://www.amazon.com/Amico-Plastic-...ds=cable+gland

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My question: can I connect the charge controller's OUTPUT anywhere that sees 12v? For example, can I tie it into the wire nuts in the cabinet over the stove? It's a 15A fuse in the power converter fuse box so I shouldn't be past half of that at 12-14V, even at peak sun.
This would work, but it is not ideal.

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That'd be most convenient for access. Easy to connect and disconnect. It's probably temporary until I figure out all the little storage places, and then drill holes and probably mount it permanently by the voltmeter by the door.
It being the controller? Given latitude, I'd mount the controller as close to the battery as I could, especially if it has a temperature compensation feature.

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I realize I may lose a bit of power getting to the battery along longer internal wires. I'm fine with that for now. Other than that, any concerns? Am I about to scramble my egg?
Sounds like you are about to embark upon an adventure. How are you attaching the panels?

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Thanks for this new obsession!
That's half the fun, no?
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Old 05-14-2013, 10:46 AM   #3
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My old panel had the wires run through a hole in the roof and sealed with Dicor. It never leaked. I just installed a new panel and ran the wires the same way and don't expect to have any issues, at least none that I'd panic about.

As for the controller I agree with Tom. Closer to the battery the better. Mine is also mounted inside, right behind where my batteries are. I ran separate 4g wires from the controller through the wall to my batteries keeping the wire as short as I could. Personally I'd never tap into existing small gauge wiring for charging.

Good luck with your install.
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Old 05-14-2013, 11:48 AM   #4
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Originally Posted by multi-task View Post
My old panel had the wires run through a hole in the roof and sealed with Dicor. It never leaked. I just installed a new panel and ran the wires the same way and don't expect to have any issues, at least none that I'd panic about.

As for the controller I agree with Tom. Closer to the battery the better. Mine is also mounted inside, right behind where my batteries are. I ran separate 4g wires from the controller through the wall to my batteries keeping the wire as short as I could. Personally I'd never tap into existing small gauge wiring for charging.

Good luck with your install.
Running 4 gauge wire doesn't do much for you. With a 90 Watt panel the maximum current could be as high as 7 amps. The only effect of larger gauge wire is maybe a fraction of a second faster charge.
Being close to the battery is only good for temperature compensation. If your battery is as should be outside, then the outside air is about the same temperature no matter where the controller is in respect to the battery.
Since I chose to make my solar panel portable and moveable I put the controller on panel frame. I have up to 35' of wire between the controller and the battery. I did use 10 awg wire but only because I had bought a 100' roll to use with my ham radio set up at home and enough left over to do the solar thing. If I would have had to buy wire for solar thing it probably would have been 14 awg or 16 awg, I could get away with using 18 awg.


It all works as planned.
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Old 05-14-2013, 11:57 AM   #5
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I've found eBay to be a good source for wire. I buy the Siamese speaker wire.

50 ft 12 Gauge Red Black Stranded 2 Conductor Speaker Wire Car Home Audio | eBay
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Old 05-14-2013, 12:21 PM   #6
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I've found eBay to be a good source for wire. I buy the Siamese speaker wire.

50 ft 12 Gauge Red Black Stranded 2 Conductor Speaker Wire Car Home Audio | eBay

That's very close to the same wire I use. Here's what I've been buying. Red/Black Zip Cord
Note this is automobile grade along with flame resistant. When we tested for UL WV-1 we would use a propane torch to get the insulation burning, then remove the torch and the insulation had to stop burning with some short time period. I don't remember what time period was, I believe it was somewhere around 5 seconds, maybe as much as 10 seconds.
The insulation is also more abrasive resistant.
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Old 05-14-2013, 12:21 PM   #7
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Running 4 gauge wire doesn't do much for you. With a 90 Watt panel the maximum current could be as high as 7 amps. The only effect of larger gauge wire is maybe a fraction of a second faster charge.
My setup isn't 7 amps, it wasn't even mentioned. My response was simply an example of what I did, not a solution for the OP wiring choice.

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Originally Posted by Byron Kinnaman View Post
Being close to the battery is only good for temperature compensation. If your battery is as should be outside, then the outside air is about the same temperature no matter where the controller is in respect to the battery.
Since I chose to make my solar panel portable and moveable I put the controller on panel frame. I have up to 35' of wire between the controller and the battery. I did use 10 awg wire but only because I had bought a 100' roll to use with my ham radio set up at home and enough left over to do the solar thing. If I would have had to buy wire for solar thing it probably would have been 14 awg or 16 awg, I could get away with using 18 awg.
I completely disagree with you. Distance between the controller and the battery has nothing to do with temperature, especially if the controller is inside and the batteries are outside. It has everything to do with the length of your wire run to reduce voltage drop. For proper temperature compensation a temp sensor at the batteries is required. Either that or risk the fire hazard of mounting a controller next to the batteries, which most manufacturers strictly state not to do.

If you're trying to push a charging voltage (14.2v-14.8v) over small wire at a great distance you simply won't accomplish what you expect. Hook up a proper meter and watch your voltage and amps, it's plain as day what long wire runs will do. Even suggesting 18g just makes no sense. With the inconsistent watts/amps coming from a mobile solar panel you'd likely never maintain a float voltage let along a charge voltage.

Larger wire in mobile setups is better because we simply don't have ideal sun conditions, so you want to maximize the voltage you get. I'm not suggesting everyone run out and buy 0g wire, use what you can afford and just move the controller as close to your batteries as you can.
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Old 05-14-2013, 12:25 PM   #8
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Originally Posted by multi-task View Post
My setup isn't 7 amps, it wasn't even mentioned. My response was simply an example of what I did, not a solution for the OP wiring choice.



I completely disagree with you. Distance between the controller and the battery has nothing to do with temperature, especially if the controller is inside and the batteries are outside. It has everything to do with the length of your wire run to reduce voltage drop. For proper temperature compensation a temp sensor at the batteries is required. Either that or risk the fire hazard of mounting a controller next to the batteries, which most manufacturers strictly state not to do.

If you're trying to push a charging voltage (14.2v-14.8v) over small wire at a great distance you simply won't accomplish what you expect. Hook up a proper meter and watch your voltage and amps, it's plain as day what long wire runs will do. Even suggesting 18g just makes no sense. With the inconsistent watts/amps coming from a mobile solar panel you'd likely never maintain a float voltage let along a charge voltage.

Larger wire in mobile setups is better because we simply don't have ideal sun conditions, so you want to maximize the voltage you get. I'm not suggesting everyone run out and buy 0g wire, use what you can afford and just move the controller as close to your batteries as you can.

Simply put, you can disagree you want, but it doesn't change the physics of battery charging.

Let's run some numbers.
First a battery will draw some higher current value at the beginning of a charge. In the case of the OP that number around 7 amps. In case with 65 Watt pane that number around 4 amps. As the battery gets closer to a full charge that current drops to around 1.5 to 1 amp.

Your 4 awg wire has a resistance .0002485 ohms per foot. I'm going to use 20' wire as an example. Total resistance then is 20 x .0002485 = .00497 ohms. Which at 1.5 amp would be a voltage drop of .00497 x 1.5 = .007455 volts or 7.455 mVolts.
Now let's look at 18 awg. Resistance per foot is .006385 ohms. At 20' that would be .1277 ohms. The voltage drop with 1.5 amp is then .1277 x 1.5 = .19155 volts. If you that's going make a big difference, OK. I guess it might keep the battery from being discharged a by a few minutes, but not enough to worry about.

Now let's take a look at 12 Awg. The same math = a voltage drop of .04764 volts.
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Old 05-14-2013, 12:45 PM   #9
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Simply put, you can disagree you want, but it doesn't change the physics of battery charging.
Battery physics is irrelevant if the batteries don't get a voltage higher than they currently sit. The physics of voltage drop occurs before the battery even begins to charge. Use whatever wire you want, but I can guarantee the norm in solar installs will be larger wire and shorter runs, especially with small low voltage solar panels. There are numerous threads on this subject already.
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Old 05-14-2013, 01:00 PM   #10
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Battery physics is irrelevant if the batteries don't get a voltage higher than they currently sit. The physics of voltage drop occurs before the battery even begins to charge. Use whatever wire you want, but I can guarantee the norm in solar installs will be larger wire and shorter runs, especially with small low voltage solar panels. There are numerous threads on this subject already.
Let's look at your points one by one.
"Battery physics is irrelevant" Battery charging physics is what it's all about.

"The physics of voltage drop occurs before the battery even begins to charge".. No current flow until the battery starts to charge, no current means no voltage drop. Basic Ohm's Law.

"Low voltage solar panels." Solar panels designed for recharging 12 volt batteries typically range in output of 18 to 28 volts. Which leaves plenty for the necessary voltage drop across the controller.

"Numerous threads on the subject"
I read through a number of them and back yard mechanics simply don't understand basic electricity. They pick up a couple buzz words and are instant experts, but have no idea how things really work. This is a continual battle of misconception and reality. Don't feel bad it's been going on since the discovery of electricity. I saw it almost 60 years ago and still going on today. Maybe even more so with internet and misconception "I read it on the internet so it must be true".
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Old 05-14-2013, 01:32 PM   #11
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Other opinions.


https://rvsolarstore.com/index.php?r...formation_id=9

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The charge controller should be as close to the batteries as possible but not in the battery compartment. Battery gases can corrode and over time destroy the electrical circuits in most solar charge controllers.
The RV Battery Charging Puzzle « HandyBob's Blog

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You must locate the charge controller as close to the batteries as you can or use BIG wire, so you actually get the volts to the battery terminals. (#10 is not big.)
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Old 05-14-2013, 01:55 PM   #12
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There are no opinions in physics ( unless you're at Princeton). Physics is physics. Byron is an E.E. This stuff is first year 3 weeks in. Drew, if you can't do the numbers you shouldn't argue. Raz
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Old 05-14-2013, 02:38 PM   #13
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..........
Hating on someones install is childish and petty. A couple of us responded to the OP to guide them in the right direction and give them ideas. If you don't like someones post keep it to yourself or present your knowledge in a more professional way expectant of your age.
Drew, you are new here. This group will spend days arguing over half full or half empty, party sunny or partly cloudy.

Don't take it seriously or it will pi$$ you off.
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Old 05-14-2013, 02:39 PM   #14
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There are no opinions in physics ( unless you're at Princeton). Physics is physics. Byron is an E.E. This stuff is first year 3 weeks in. Drew, if you can't do the numbers you shouldn't argue. Raz
I'm past arguing over this.
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