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Old 02-13-2020, 12:45 PM   #1
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2018 25' Flying Cloud
Ann Arbor , Michigan
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Solar Install Split Between Airstream and TV

Without the Airstream and YouTube DIY community, we would not have been able to complete this project. In that spirit, we would like to add to the body of knowledge with our twist on the solar install which we split between the tow vehicle and Airstream. ("Split" = Tow Vehicle and Airstream have have separate solar panels, batteries, chargers etc and are able to be connected to allow transfer of electricity from tow vehicle to airstream as needed).

Advantages
1. Flexibility: Can leave Airstream parked in a less solar efficient space (shade) and move the tow vehicle to sunny spot
2. Easier to tilt panel on Tow Vehicle
3. Tow vehicle alternator is a secondary charge source. Every time you drive the battery recharges.
4. Can get away with only 4 panels on the 2018 airstream and use the Airstream prewired solar cable (lower gauge) and not have to run new (larger gauge) cable.

Disadvantages
1. Cost: increased components: 2nd charge controller, dc to dc converter, cables, breakers.
2. Decrease in efficiency IF bulk transfer of energy from tow vehicle battery to Airstream battery via dc to dc converter (78% on 12 volt systems if measured via watts)
3. Extra weight on the tow vehicle

PS:
Also included an idea for the Airstream Jack disconnect security switch. (Basically cuts the electricity to the jack when camping, so it can’t be accidentally or intentionally activated and ruin your stabilizers)
Links for Components discussed in the video

Video Link
https://youtu.be/n-hRVygLuYk

Video Index
0 - Intro
3:02 - Tow Vehicle Install
10:24 - Outside Airstream Install
12:53 - Inside Airstream Install
26:00 - Transfer Switch Diagram
26:14 - Jack Disconnect Switch (mislabeled on the video)

AIRSTREAM PORTION OF THE INSTALL
-Four 100 watt Renogy Solar Panels. Wired: two in a series and two in a parallel.
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Old 02-20-2020, 07:43 PM   #2
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Apollo Beach , Florida
Join Date: Feb 2017
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Quote:
Originally Posted by MandN View Post
Without the Airstream and YouTube DIY community, we would not have been able to complete this project. In that spirit, we would like to add to the body of knowledge with our twist on the solar install which we split between the tow vehicle and Airstream. ("Split" = Tow Vehicle and Airstream have have separate solar panels, batteries, chargers etc and are able to be connected to allow transfer of electricity from tow vehicle to airstream as needed).

Advantages
1. Flexibility: Can leave Airstream parked in a less solar efficient space (shade) and move the tow vehicle to sunny spot
2. Easier to tilt panel on Tow Vehicle
3. Tow vehicle alternator is a secondary charge source. Every time you drive the battery recharges.
4. Can get away with only 4 panels on the 2018 airstream and use the Airstream prewired solar cable (lower gauge) and not have to run new (larger gauge) cable.

Disadvantages
1. Cost: increased components: 2nd charge controller, dc to dc converter, cables, breakers.
2. Decrease in efficiency IF bulk transfer of energy from tow vehicle battery to Airstream battery via dc to dc converter (78% on 12 volt systems if measured via watts)
3. Extra weight on the tow vehicle

PS:
Also included an idea for the Airstream Jack disconnect security switch. (Basically cuts the electricity to the jack when camping, so it can’t be accidentally or intentionally activated and ruin your stabilizers)
Links for Components discussed in the video

Video Link
https://youtu.be/n-hRVygLuYk

Video Index
0 - Intro
3:02 - Tow Vehicle Install
10:24 - Outside Airstream Install
12:53 - Inside Airstream Install
26:00 - Transfer Switch Diagram
26:14 - Jack Disconnect Switch (mislabeled on the video)

AIRSTREAM PORTION OF THE INSTALL
-Four 100 watt Renogy Solar Panels. Wired: two in a series and two in a parallel.
MandN,

Welcome to AirForums and thank you for sharing your unique installation. I am confused as to why you installed two panels on your Airstream's roof in series and two panels in parallel. I believe that would be very inefficient because the total voltage of a parallel connected array is determined by the solar panel of the lowest voltage. Therefore, your four panels become three panels because the series-pair's doubled voltage is reduced to the single panel voltage of the other parallel connected panels. I would either connect all four panels on the Airstream's roof in parallel or I would connect the panels in two series pairs. Read this link which explains this in greater detail: https://solarpanelsvenue.com/mixing-solar-panels/

You should be able to get 30A of charging from the four panels on the roof in full sun around noon under a large load. A large load would be when running your refrigerator on electric from the inverter. With your panels configured as a parallel pair and a series-pair, I believe you will only see about 22.5A, or a 25% loss of efficiency. Test this out and see if you can get near 30A from your Airstream's Victron controller without your truck's solar connected.

Please share the results of this test and other performance data from your system as you use it so we can all learn from your unique configuration with panels split between the tow vehicle and Airstream with two separate solar controllers.
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Sold: 2017 FC25FB, 316 nights 40,150 miles, 400W Solar - Produced 200 kWh in 216 days
2013 Casita SD17 89 nights 16,200 miles
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Old 02-20-2020, 08:37 PM   #3
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I also have the same question.... why would you wire one pair in series and one parallel.

Your voltage s do not match.
One pair is running at 34 volts at 5.6 amps and the other pair is 17 volts at 11 amps. They are fighting each other and you are only getting 17 volts at 5.6 amps.
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Old 02-24-2020, 07:11 PM   #4
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Ann Arbor , Michigan
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That's why I love airstream forums, thank so much for catching my mistake. I'll explain what happened. I was planning to do a standard series-parallel wire (two panels connected in a series in parallel to the other two panels also connected in a series - 34 volt system).
As an aside, I was always worried about partial shading that series arrays are subject to but did not know how much of a problem this actually is on the road. I was surprised to discover that airstream beefed up its solar cable from 10 to 8 gauge (still too little in my opinion) but suddenly voltage drop was not as big of an issue for a 400 watt system. So without researching, last minute I decided to 'split the difference' thinking that I was going to get a mean voltage of about 22 ((17+17+34/3)and ended up in this pickle. So it turns out for the last 3 months unplugged we have been actually using a 300 watt solar system on the airstream and 200 watt system on the truck, that's good to know but you bet I'm going to rewire and get back the 25%.

Since we started our trip, I have always dismissed our puny airstream solar yield due to winter sun angle, as we started using this system late fall, but it always bothered me how much we were loosing even in full winter sun. For example the most we were able to produce was about 240 watts (recently and at the start of our trip in the late), which makes sense now, as we were running essentially a 300 watt max system.


The question now is how to rewire - serial-parallel as I planned originally (2 in series parallel to the other 2 in series) or go with all parallel? Given our proclivity for camping in areas with trees, I think I'm leaning toward parallel and the 3.5% voltage drop (per voltage drop calculator http://calculator.net) be damned. I also wonder about the winter sun angle issue, for the last 3 months we were camped near NOLA with the airstream in an east to west orientation, so with the sun in the southern sky the 1/2 of the series array and 1/2 of the parallel array was slightly sloped toward the sun and the other half slightly slopped away from sun. The slight slope is due to the curvature of the airstream. I tried to correct it with adjustable mounting brackets for the panels but there is still a slight slope. I wonder which array is more efficient in this situation or are they equivalent. Heck I suppose I can test it by just plugging and unplugging since I have both of them on my roof :-). Predictions, thoughts?

BTW
Airmiles I read bunch of your posts in preparation for the install and continue to learn from you and others on this forum.
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Old 02-25-2020, 06:49 AM   #5
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Of course if it were my installation, I'd use series-parallel on the Airstream roof for the reasons I keep posting. An MPPT controller is more efficient when running at the doubled voltage of series connected pairs of 100W panels. When panels are connected in series-parallel, the Airstream's 10 gauge prewire's voltage loss is equivalent to using 4 gauge with parallel. A Victron solar controller input needs battery voltage plus 5 volts to turn on which happens sooner when running at 34V. My series-parallel configuration has supplied all the power I needed for over 97% of the days its been used. A generator was used on the other 3% of the days because of the lack of sun from either dark rain clouds or a complete canopy of trees, not because of shading issues from roof obstructions, a light canopy of trees, or overcast conditions. Why accept 3.5% voltage loss with parallel when you can have less than 1.75% loss with series-parallel? I would configure series-parallel with 100W panels even if I had 4 gauge running between my roof and solar controller.
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2018 Globetrotter 27Q, 36 nights 5,235 miles, 600W Solar - Produced 50 kWh, PD4655L, 6V Batteries, Champion DualFuel, ProPride, 16" tires, 2019 F250 PSD
Sold: 2017 FC25FB, 316 nights 40,150 miles, 400W Solar - Produced 200 kWh in 216 days
2013 Casita SD17 89 nights 16,200 miles
(Daytona 2/20)
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