Another Solar Solution - Fiberglass RV


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Old 05-23-2006, 10:17 PM   #1
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For those of you who may be interested in a solar generator this summer, here is a description of the system we put together last year. Similar pre-packaged solar systems are available now from Costco and Harbor Freight, and they appear to be a great deal both from the perspective of cost and convenience in not having to track down all of the separate components. We put together our system before the packaged systems were available, and in hindsight I would have purchased the package rather than the separate components (cheaper and easier). Nevertheless, we thought it may be helpful to post the details of our system. The primary advantages of our system are that you can easily customize to meet your power needs, you can build it from other components that you may have on hand, and the system plugs directly into your 7-pole trailer receptacle (or that of your neighbor when they need a boost).

We assembled this lightweight, portable, and versatile solar system to fully recharge the external 12V DC deep-cycle battery on our 1984 Casita 16 ft. trailer. The charging system works well when dry camping or when you just feel like capturing valuable energy free from the sun (see www.rvsolarelectric.com). The charging system consists of the following components: two primary solar panels (18 watt each), one accessory solar panel (10 watt), and a weather-proof field box that contains a 12V cigarette lighter input receptacle, a charge controller, a toggle switch, an analog voltage meter, and a standard 7-pole output vehicle receptacle.

The two primary solar panels are identical ICP Solar Battery-Saver SE (18 watt / $120 each at GI Joes) panels that are rated at a maximum rate of 1,200 mA at 15 V DC in full sunlight. These two 18 watt panels were joined together with a pair of 1” X ½” wood supports across the back, and they are mounted into a couple of steel brackets bolted into the bottom rung of a three-step aluminum ladder. A plug-and-play type cable connects the two panels at their base and raises their combined power level to 36 watts.


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The mounting brackets consist of two Stanley “L” steel corner braces that were dipped in black “Rubberize-It” coating, and then bent at 90 degrees halfway along one of the “L” arms. The “L” brackets are affixed to the bottom ladder rung with ¼“ stainless bolts held by wing-nuts to allow for easy removal. We had to drill four holes in the bottom rung of the ladder to attach the mounting brackets. We have found it useful to bring this small lightweight ladder along during our camping trips not only to hold the solar panels, but also to step up to reach the top of the trailer vent, to reach the racks on top of our truck canopy, and to tie up a clothesline in a nearby tree.


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The accessory solar panel is a Solarex MSX10 (10 watt) panel that is rated at a maximum rate of 0.6 A at 17V DC in full sunlight. The mounting bracket for this accessory panel consists of a small photo tripod equipped with a bent aluminum “U” bracket. The combination of the tripod and “U” bracket allows the 10 watt panel to rotate freely and tilt into the sun. The cable from the accessory 10 watt panel plugs directly into the primary solar panels to yield a total solar power generation system of 10W + 18W + 18W = 46 watts (3 amps). These solar panels can be easily moved around in the parking area during the day to remain in the direct sunlight and capture the greatest amount of solar energy.


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Five more parts of the charging system are contained within a plastic weather-proof field box. First, we trimmed a ¼” thick white plastic cutting board to fit snugly inside the field box to serve as a base and to provide a raised surface that will let the wires run neatly underneath the switch and volt meter. Then we used a dremel tool to cut out holes in the side of the field box for the input and output receptacles. The cable from the solar panels ends in a male 12V connector that is plugged into a marine-grade female 12V DC receptacle that has a rubber cap to keep out water. The positive (white) and negative (black) wires run from the female 12V receptacle into the solar input terminals of a Morningstar SunSaver-6 charge controller (model SS-6-12V). The charge controller cost about $40.00, is rated at 6.5 amps and puts out a Pulsed Width Modulation (PWM) regulated charge of 14.4V (or 14.1V for a sealed battery). A green LED light indicates that the solar panels are charging the trailer battery. Black and white wires from the load terminals of the charge controller are routed through a hole in the white plastic base and into a lighted red automotive rocker switch ($4.00 from RadioShack), and then into an analog DC volt meter (model 22-410 / 0-15V DC from RadioShack $13.00). Finally, the positive and negative wires exit the battery terminals from the SunSaver-6 charge controller and run out to a standard female 7-pole vehicle-side receptacle. The 7-pole electrical plug from the trailer cable connects directly into the 7-pole receptacle in the field box and carries the regulated charge to replenish the deep-cycle battery. The field-box costs about $13 at Bi-Mart, and it has a lockable hinged lid and a rubberized gasket to keep out the rain, drizzle, and spiders.

During the summer, we used this solar charging system for a three night dry camping trip on the northern Oregon coast. We found that the combined system generates somewhat less charging power than the calculated value of 3 amps, but the system does an adequate job of recharging our deep-cycle battery to keep up with our use of electricity. In the future, we plan to install a combination volt/amp meter inside our trailer so we can keep track of our electricity use and easily monitor the status of our trailer battery.

Special thanks to participants of the 2004 Oregon Gathering whose ideas helped create the inspiration for this project.

Steve
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Old 05-23-2006, 10:48 PM   #2
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Interesting idea to use the pigtail as an input to the battery. I take it you are coming straight off the controller to the charge line?

How is it grounded? (At the pigtail) I thought the ground from the contoller had to be straight to the battery, but I guess it really shouldn't make a difference. It all ties in eventually.

My controller is mounted inside, just above the battery and wired direct. There is a solid "box" where my AC line runs into the trailer, behind an access hatch. The solar panel lines to the controller are run thru the back wall of this box and my panels are connected via a bannana plug on the controller input lines.

The hatch is closed when in use to keep water from gumming up a good thing.
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Old 05-24-2006, 07:46 PM   #3
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Quote:
Interesting idea to use the pigtail as an input to the battery. I take it you are coming straight off the controller to the charge line?

How is it grounded? (At the pigtail) I thought the ground from the contoller had to be straight to the battery, but I guess it really shouldn't make a difference. It all ties in eventually.
Use of the 7-pole pigtail as the battery input works out great! I don't have to take the top off the battery box to hook up the pos / neg clips. Instead I just plug the pigtail into the 7-pole receptacle in the field box. And yes, the regulated output from the the SunSaver charge controller is wired directly to the 7-pole receptacle where it charges the trailer battery.

My trailer battery is grounded to the trailer frame. I have not added any additional ground wires to the solar system. I didn't believe that additional grounding would be required when I built the system, but I could be wrong about that. It does all tie in eventually, and because of the use of the pigtail my charge controller is located very close to the battery and frame/ground point.

Another nice feature about this set-up is that I can just use the smaller 10 Watt (or smaller) accessory panel when I'm at home and all the battery needs is a trickle charge.

All you have to do is keep your fingers crossed and hope that it will be sunny outside.


Steve
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Old 05-25-2006, 02:01 AM   #4
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I mounted the panel on the roof of the Scamp because it is pretty fragile and the wind or a bump could be expensive. I put a meter on it before I mounted it and pointed it at different angles to the sun and found it really wasn't too fussy about being aimed directly at the sun so I don't worry about that. Up there and out of the way works for me.
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Old 05-25-2006, 11:14 PM   #5
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I have also noted very little difference in where or HOW the time was pointed. I know there are formulas and data sheets explaining how to get maximum efficiency. I have found that as long as it is IN the sun, and at a 45 degree angle or so, even facing straight up, it does fine. Even if you hit an 18volt sweet spot, the controller is going to regulate to 14.2 anyway.

BUT, in the shade, I have noticed a difference, so thats why I want to be able to set it where it gets direct sun.

I am going to have to rethink the pigtail idea. This seems a great one to me, tho what I have works just fine. It's no more difficult to connect than it is the power cord to an ac outlet at a full service sight. My controller and other stuff stays put too. shg
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Old 05-26-2006, 08:05 PM   #6
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Shirley - your roof-mounted system sounds great and hassel free. What does the mounting system look like? I'm also keenly interested in mounting my solar panels on the roof at some point in the future. My primary concern is that it will be difficult to clean out the leaves and pollen and gunk that will accumulate in that narrow space between the panels and the roof, so I want to devise some sort of easy-on / easy-off system rather than a permanent mount. It would be great if those of you FGRVers who have roof-mounted solar panels would post your photos here so we can see what works out best. Please post your roof-mount photos! Colin K. posted a great photo of his custom aluminum frame and support legs on another solar thread, and I would like to see more.

Similar to Gina, with my ground-based system I haven't noticed much difference in the charging rate as long as the panels are located in the sun, but the charging is definitely slower in the shade. The step ladder doesn't let me change the angle much, but I don't think it makes much of a difference. The SunSaver charge controller puts out 14.4 V as long as there is sufficient sunlight. Here are a few more detailed pictures of the 7-Way / Pigtail connection. The pos / neg wires from the charge controller are routed right into the standard 7-Way vehicle end connector, and the 7-Way / Pigtail from the trailer plugs right in. I believe that the charging path to the battery is the same as when you are underway and the power generated by your tow vehicle serves to recharge the trailer battery. The 12-V cigarette-lighter plug shows the input from the solar panels.


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Incidentally, you can also use the system as a trickle charger (or hook it up to your neighbor's trailer at a time of need). In this case, I've just plugged in a single 10 Watt solar panel. Simple! Easy to pack up too.



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Old 05-27-2006, 11:25 AM   #7
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Great Idea's here. I am thinking of doing something similar but with the controller in a box and the 400w inverter. I can flush mount the inverter to an opening in the box then simply run an extension into the trailer. It will solve the short distance required between inverter and battery problem. I think Colin said he ran the inverter wiring right into the trailer and attached it to a recepticle. I guess the main issue is keeping the inverter receptcle covered against the elements and perhaps heat build up but it should be more easily taken care of outside the Trill than inside. Perhaps a small piece of heat resistant material on the bottom of the box for the inverter.
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