Solar charging system completed - Fiberglass RV


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Old 12-07-2013, 01:58 AM   #1
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Name: Russ
Trailer: Scamp 16' side dinette, Airstream Safari 19'
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Solar charging system completed

I put together a robust portable solar charging system to extend boondocking ability. It is most likely overkill, but should have some functionality under less than ideal conditions. I tried to keep all voltage drops under 2 %, which required heavier conductors than what most folks would like to handle. The panels I went with are Renogy 100W, and measure about 47" x 21" and weigh about 16lbs. I fabricated "kikstands" that prop the panels at infinite angles to optimize collection of rays. I decided to leave the panels separated from one another to add flexibility in positioning choices.

The MPPT controller is mounted at the trailer tongue in a NEMA enclosure for weather protection. There was no desirable interior space for the controller in the 16' Scamp. By mounting the controller at the trailer instead of at the panels meant that the 30’ long wire run could be of lighter gauge. I selected 8/2 marine cable for that run which should keep the voltage loss near 2%, and is still flexible and easy to coil and handle. I used the MC4 connectors at the panel end, as that is industry standard, and weather proof. At the controller end I selected Anderson Powerpole connectors which can be connected under load and are beefy.

Inside the controller box I mounted a Midnite Solar baby box which houses a 50 A breaker that serves as a battery disconnect and fuse. Also in the baby box are 2 10 amp breakers which protect the panel wiring and act as disconnects for the panels. I also mounted the Trimetric meter shunt in the NEMA box to get it out of the weather. The components in the box create heat, so I cut a hole in the bottom of the box and fabbed a bug screen and frame to allow cooling air in, and drilled a couple of 2” holes in the top of the box to let the hot air out. I kludged up some weatherproof vent covers out of PVC building weatherheads that should be functional, but ugly. My tig welder is possessed with demons, so I couldn’t fab a sexy vent from aluminum. Maybe later? The wire from the controller to the battery is about 5’ long, so 4ga. Is adequate with little drop.

The night I finished the system I turned on the Fantastic fan and let it run all night on high and when I went out the next morning at about 10 AM the battery was down to 75%. The sky was completely overcast and gray. I had only one panel wired due to one defective MC4 connector, so I put the finished one outside and hooked it up. The Trimetric read only 12.8v and 2 amps. I left it for a couple of hours while I worked to repair the other connector. Once the repair was complete I put the other panel out and took another reading. Voltage still dismal, amperage 4, percent of charge 78%. We got 3% from the one panel with only 12.8v! By 2 PM the panels were totally shaded and not doing anything, so I put them to bed. We were only 82%. There just wasn’t any sun showing that day. The next day I Put the Panels out at about 11 AM. The sky was very cloudy, but the sun would break through at times. When the sun shown I would see 14.8V and 13A. Clouds would lower the numbers considerably. By 2 PM the sun went away and I removed the panels. In 3 hours it harvested enough juice to reach 97% charge from 87%. I think this system will be able to bring back the battery from the previous evenings draw, even if the sun is hiding. I have yet to use the furnace and CPAP all evening, but would like that option. I’ll do some testing at home to see how it does and report back.
Russ
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Old 12-07-2013, 03:38 AM   #2
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Thanks for the detailed equipment description. Very useful info, especially about which connectors you chose. I'm a big fan of using large wire to minimize loss, even if some would say a bit too large. Why have any of the precious energy go into IR loss?

What size battery in your set up?
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Old 12-07-2013, 06:51 AM   #3
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pictures, pictures...
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Old 12-07-2013, 03:02 PM   #4
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Are you using the humidifier in the CPAP? That's whats drawing the amps.
I'm trying to rig up a low current humidifier that will feed into the air hose.
Its a bear to try and use a CPAP in dry air conditions without the humidifier.
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Old 12-07-2013, 03:31 PM   #5
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Originally Posted by jwarner View Post
Are you using the humidifier in the CPAP? That's whats drawing the amps.
I'm trying to rig up a low current humidifier that will feed into the air hose.
Its a bear to try and use a CPAP in dry air conditions without the humidifier.
Jerry,
I fill the tank with water, but don't heat it. Just passive evaporation.
Russ
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Old 12-07-2013, 03:40 PM   #6
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Originally Posted by LeonardS View Post
Thanks for the detailed equipment description. Very useful info, especially about which connectors you chose. I'm a big fan of using large wire to minimize loss, even if some would say a bit too large. Why have any of the precious energy go into IR loss?

What size battery in your set up?
Leonard,
I don't recall the amp hour rating, but the fitment size is group 27. It is a Costco Kirkland marine deep cycle, and very commonly sold there. It is probably around 110 amp hour.
Russ
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Old 12-07-2013, 03:56 PM   #7
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Originally Posted by cpaharley2008 View Post
pictures, pictures...
Jim, OK I'll take a stab at pictures.

I can't figure out how to add captions to pics, so will comment here.
First shot is showing NEMA box location on trailer. Second shot shows 1.5" x 2" steel tube mounts welded to trailer tongue. Third shows the propane line passing through the tube. (nothing's easy!) Last shot is box on table being readied for components.
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Old 12-07-2013, 04:21 PM   #8
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More progress shots.
1. NEMA box on table being readied for components.
2. Bottom of box showing vent window.
3. Weather head modified into exhaust vent.
4. Box installed on trailer.
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Old 12-07-2013, 04:28 PM   #9
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Box interior. Shunt is mounted lower left. Panel connection is via pig tails with Anderson Powerpole connectors. The panel wires are fed through the hole in the bottom of the box and connected to the pig tails keeping them out of the rain. The hole in the box will have a slide cover over it to keep out insects.
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Old 12-07-2013, 04:54 PM   #10
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Panel pictures

Panel sits horizontally for stability and resistance to wind. Kickstand is constructed of aluminum for lightness. The angle adjustment is infinite to optimize sun angle.
The tab in the middle photo swivels and provides a staking anchor for windy days. Also the mini cam cleat which is sailing hardware for controlling lines.
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Old 12-07-2013, 05:14 PM   #11
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1. Kickstand hinge tab fabricated from aluminum angle.
2. Hinge tab in place.
3. Rope tie in eyelet.
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Old 12-07-2013, 05:38 PM   #12
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I really like the kickstand. It is on the list to add to my portable solar. What is your source for the metal rods? Are there other stock items you used.?
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Old 12-07-2013, 05:49 PM   #13
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A bit late to point his out now, but had wired your solar panels in series (charge controller wired to panel one, panel one wired to panel two, then panel two wired back to the charge controller) instead of in parallel (charge controller wired to both panels one and two, then the panels wired back to the controller) you could have gone with 14g wire and had an almost identical drop in current. Unlike older Pulse Wave Modulation (PWM) controllers, most most modern Maximum Power Point Tracking (MPPT) controllers can handle two, sometimes even three or four panels wired in series, and wiring them in series increases the voltage and watts carried by the system without increasing the loss-inducing current.
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Old 12-07-2013, 07:26 PM   #14
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Originally Posted by Paul Braun View Post
I really like the kickstand. It is on the list to add to my portable solar. What is your source for the metal rods? Are there other stock items you used.?
Paul,
The rod is 1/4" diameter aluminum of unknown alloy purchased as a remnant. It bent easily, so may not have been T6 temper. If you don't have a way to weld aluminum you could substitute 3/4" square aluminum tube from Home Depot and just have a single leg hinged at the end. There are really no side forces to be overcome, so the single leg would suffice. You could also use many other means to fasten the rope to the leg as well. Lots of ways to skin the cat..
Russ
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