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Old 02-05-2020, 06:49 PM   #1
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8awg Solar Prewire, now what?

Hi All,

Looking to finalize a solar order with AM Solar for our 25 GT FBT. After reading and reading and reading some more, much stuff, several times over, I had come to the conclusion that i would go ahead and up the down wire to #4, from the factory #10. In the end I would install 4/100w panels in parallel. Much of that decision was based on straightforwardness of coming into the diagonal chase in the bathroom, 8 feet later, under the curbside twin bed, where I will covert to a lithium bank of 300-400 ah. As well I could also run additional lines for satellite, weboost, etc in that same chase, same combiner.

So, with my plan in place, I took the top off the curbside bed, immediately saw the solar pre-wires and discovered they are not #10, but rather they are #8!

After knowing the pre-wire is at 8 and not 10, I now am wondering if a series parallel deserves more consideration, simply based on the simplicity of the install. The Airstream folks do not recommend series parallel and under no circumstances do they feel 4 panels on the pre-wire is ok. That being said, they were referring to #10, when making that comment.

Does the difference between 8 and 10, change much? I am not in hurry to drill a couple holes in a new Globetrotter, however, I will if it's going to make a noticeable difference or contribute to a better capacity match. I would not consider a few watts to be "game-changing"! I am more concerned with safe capacities rather than wringing every last possible watt from the sky. I like being 75% of capacity, rather than 99% or 104%!

Lastly, this is not a series-parallel versus parallel question, rather comparing 400w series-parallel on #8 versus #10. Anyway, the bathroom chase is open and #4's could be accommodated for, very easily.... or so it appears, ha ha!

Being in the upper midwest, we see some overcast skies, however I can always upgrade the wire later if I find more than 4 panels are a need or the shading is wreaking havoc and I want to try fully parallel.

Thank you all in advance, you are a wonderful resource!
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Old 02-05-2020, 07:10 PM   #2
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8ga can more than carry your 4 panels load. Each panels at 6 amps output max would only be 24A with a full parallel configuration. 8ga wire can carry 40A.

See attached chart.
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Old 02-05-2020, 07:34 PM   #3
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I use this chart almost daily. The main thing to remember on DC circuits is that DC “flows” in one direction so you have to calculate using both there and back. (Both positive and negative leads).
Example: a 15’ run would calculate out as a 30’ circuit for gauging wire size
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Old 02-05-2020, 07:38 PM   #4
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Another important factor to consider is the temperature rating of the wire insulation. 90C rated wire can carry more current (without melting) than 75C wire, and I wouldn't use anything less than 75C.
Check the temperature rating of the prewire installed by Airstream.
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Old 02-05-2020, 07:49 PM   #5
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Quote:
Originally Posted by markdoane View Post
Another important factor to consider is the temperature rating of the wire insulation. 90C rated wire can carry more current (without melting) than 75C wire, and I wouldn't use anything less than 75C.
Check the temperature rating of the prewire installed by Airstream.
It should be 105C rated
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Old 02-05-2020, 08:37 PM   #6
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Yep, the factory is stamped 105c.

I am guessing the factory pre-wiring doesn't take the most direct routing and it could 25 or more feet. Anyway at 50 feet (counting the return) carrying 25 amps, awg lands in the 4 range. It appears however that in a series-parallel connection, 8 would be more than fine. When it comes to "melty wires", a healthy buffer is good with me!

And that really is the question, #8 in series-parallel or spend $125 and 2 hrs to run #4 for full parallel, and forget about wire temp inspired concerns.

Thanks again guys!
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Old 02-05-2020, 08:41 PM   #7
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Yep, the factory is stamped 105c.

I am guessing the factory pre-wiring doesn't take the most direct routing and it could 25 or more feet. Anyway at 50 feet (counting the return) carrying 25 amps, awg lands in the 4 range. It appears however that in a series-parallel connection, 8 would be more than fine. When it comes to "melty wires", a healthy buffer is good with me!

And that really is the question, #8 in series-parallel or spend $125 and 2 hrs to run #4 for full parallel, and forget about wire temp inspired concerns.

Thanks again guys!

Based on what I’ve heard and know about guys like “us”. Run the 4AWG and forget about it.
You will never be able to let it go if you don’t. (It will bother you)
Don’t let it bother you. Run the 4AWG.
And as stated before with the combiner box you will have a pathway for any rooftop accessories to the inside.
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Old 02-05-2020, 08:52 PM   #8
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Perfect, makes sense, thank you for the nudge!
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Old 02-06-2020, 07:18 AM   #9
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Or run multiple 10s. Then add extra charge controllers for each circuit. This way you don't have to worry if one panel or group of panels is shaded. Gives you better control of the charge. Costs more for the high end charge controllers. But there's plenty of cheaper ones out there that will still function just as well.
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Old 02-06-2020, 08:09 AM   #10
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I would definately use the 8 AWG prewire with four 100W panels in parallel or six 100W panels in series-parallel pairs. I'm running 600W series-parallel pairs on the thinner 10 AWG prewire. For the full story with performance data, read the Solar Show and Tell Thread. https://www.airforums.com/forums/f44...ml#post2329805
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Old 02-06-2020, 09:53 AM   #11
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Location of prewires

Is there anywhere I can see a drawing of where 2018 22FB Sport factory wires are threaded in the chassis? I wonder about how to thread 4/0 replacing the factory solar prewire. I don't want to be doing a lot of guessing about how it is done.
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Old 02-06-2020, 10:42 AM   #12
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Solar panels can produce up to 25% more power in cold weather, this also has to be factored in.
As was mentioned above, I would go full parallel, and wire with 4 awg and forget about it.
And if you ever want to upgrade to more capacity in the future (adding panels or replacing them with more efficient technology, who knows what will come to market?) you will have the infrastructure to handle it.
It's an Airstream, technology can evolve quite a bit within its lifetime.
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Old 02-06-2020, 11:00 AM   #13
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Quote:
Originally Posted by lilboomer View Post
Is there anywhere I can see a drawing of where 2018 22FB Sport factory wires are threaded in the chassis? I wonder about how to thread 4/0 replacing the factory solar prewire. I don't want to be doing a lot of guessing about how it is done.
The discussion is centering around 4 AWG not 4/0 AWG. 4/0 is extremely large diameter wire.

Can't help you on the routing although I have heard a number of installers say they route the wire down through the exhaust vent of the refrigerator if the trailer has a roof-mounted exhaust vent. Using this method, no holes are needed through the skin of the trailer.
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Old 02-06-2020, 11:28 AM   #14
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I'd you are using a mppt charge controller, go with the series parallel configuration.

2 reasons

1, the "start charge" voltage needs to exceed battery voltage to get any kind of charge going, on overcast days, you may never exceed battery voltage in a parallel setup. Also, the charge starts earlier in the day, and finishes later. Giving you more charge time.
The mppt controller will take advantage of every watt that it is given.

2, voltage doubles, current stays the same.

A watt is a watt. Regardless of current or voltage.
Example, 100w = 100v, at 1amp. (Very small wire needed to run 1 amp) 100w also = 1v at 100amps.
Much larger wire necessary.

If, with your wire length, you can get away with #8, and have no plans to add another panel or 2, then stick with the 8ga.



Higher voltage also adds greater efficiency, it reduces heat, and overcomes small resistances more easily.
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Old 02-06-2020, 11:34 AM   #15
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I believe it would more of a matter of where to run the new heavier gauge wire, versus physically replacing the factory. Unless you plan to remove interior panels, not sure removing the existing prewire is possible or maybe sensible is a better word.

Lastly, 4-awg and 4/0 are two very different gauges!

If you know where your "rat's nest" of wires are, perhaps towards the front of your trailer, you will likely be able to find (2) terminated #10's, one being green and the other being yellow, this is what you would run into a new solar controller, before going off to the battery/bussbar. That is assuming you were going to use the factory pre-wire.

Maybe search solar in the 22' forum, that would provide for more "model" specific info! Or, starting a new thread in the this same solar section, with some additional details.

Whether you need a heavier wire is a different question. Folks will want to know how many panels, expected AH needs etc... in order for them to be of the most help to you.
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Old 02-06-2020, 11:53 AM   #16
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Originally Posted by lilboomer View Post
Is there anywhere I can see a drawing of where 2018 22FB Sport factory wires are threaded in the chassis? I wonder about how to thread 4/0 replacing the factory solar prewire. I don't want to be doing a lot of guessing about how it is done.
I am also at this cross roads, use factory prewire on series/parallel or install 4 AWG to accommodate 4+ panels on parallel.

If anyone has installed upgraded solar wire on a 27 FB I would really appreciate any info you have regarding where to thread the cable from the roof to the front compartment. I have been searching for days without any luck.

After receiving a large estimate to have this done, I am more than willing to give it a go myself. It just so happens that I have 25' each of red and black 4 AWG tinned copper marine cable in the garage, which hopefully is enough.
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Old 02-06-2020, 11:59 AM   #17
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Can't help you on the routing although I have heard a number of installers say they route the wire down through the exhaust vent of the refrigerator if the trailer has a roof-mounted exhaust vent. Using this method, no holes are needed through the skin of the trailer.
Exactly! Did exactly that for my install: no holes drilled anywhere on the roof. Used AM Solar feet for the 5 Renogy panels (VHB taped with a 1/4" Sikaflex covering over and around each foot), ran 4 AWG wires from the combiner box through the fridge vent (drilled two holes in the vent side wall to install two AM Solar Liquid Tight Srain Reliefs for the + and - 4 AWG wires); the combiner box was VHB taped and Sikaflexed.
All panels are wired in parallel to the combiner box with 10/2 wiring through an appropriate AM Solar Liquid Tight Srain Relief; I then drilled the plywood floor of the back of the fridge cabinet to connect the two 4 AWG cables from the combiner box to the MPPT controller in the front of the trailer under the L couch. Connected the MPPT controller temperature sensor to the battery bank, connected the current shunt (500A/50mV) with a shielded twisted pair to the controller's monitor, and then connected the MPPT controller output (4 AWG cables) to the battery bank and it all worked!
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Old 02-06-2020, 01:31 PM   #18
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Hermes, that's awesome!

Hope my install goes as smoothly! Not really too much I am concerned about, with regard to the solar panel install and rewire.... I suppose that might change!
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Old 02-06-2020, 04:44 PM   #19
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I didn't mention that you need to remove the fridge vent cover and bug screen to be able to install the 2 strain reliefs and pass the 2 wires. I reinstalled the vent cover over a thick butyl tape, tied down with Olympic rivets which puncture the tape to get into the original rivet holes in the roof; shaved and polished the rivet heads with a Dremel to look like the original ones.
Good luck!
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Old 02-06-2020, 04:56 PM   #20
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I use this chart almost daily. The main thing to remember on DC circuits is that DC “flows” in one direction so you have to calculate using both there and back. (Both positive and negative leads).
Example: a 15’ run would calculate out as a 30’ circuit for gauging wire size
Whoops. I didn't calculate the length of the round trip, which is how I wound up with 6 awg from the roof...good to up to 18 feet at 2 percent loss for my four panels in parallel. My run was certainly more than 9 feet *each* way, so the chart prob would have called for 4 awg. So my losses might be higher than 2 percent after all. Fortunately my system has been working great for me though I'm probably not wringing every last watt. But I do float every day, so life is good!
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