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Old 07-08-2016, 09:13 AM   #1
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Has anyone added roof-mount solar to Coachmen Prism?

Wife and I are about to begin new ventures as we ready to purchase a class-c Sprinter, lease our home, and drive into a year of travel as we search for a new homestead. While we feel confident about our class-c MB Sprinter decision, we have not yet decided which make. We are persuaded toward a 2016/17 single slide unit with the diner, closet, and queen bed on the port side. However, I wish to add a few things to the motorhome which I believe will greatly enhance our boondocking comfort. While most of the things I wish to add are quiet simple, three items concern me because of available space or necessary coach modification, these are: 1) 300 watts roof-mount photo-voltaic, 2) whole-house reverse osmosis for freshwater, and 3) shore AC power surge protection.

In this thread, I would like to focus on the photo-voltaic solar panels, and leave the other two topics to another thread. I have already calculated my average daily power consumption and have concluded that 300 watts with a MPPT controller will generally satisfy my daily energy recharge rate on a weekly schedule (already compensated for a flat panel roof-mount with seasonal variation). I am, however, concerned about available roof real estate for two solar panels on a class-c Sprinters. Has anyone here accomplished such installations with ideas and experience about how I should proceed?
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Old 07-08-2016, 10:49 AM   #2
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There is a lot of information already in older strings. Search MBS, Solera and Forester strings for "solar" to get up to speed. I also suggest the Jack Mayer website to understand the practical electrical and mounting details. 300 watts flat mount with mppt is about right to boondocks with MBS. We have 400 watt on pwm and no shortage of power.
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Old 07-08-2016, 12:08 PM   #3
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There is a lot of information already in older strings. Search MBS, Solera and Forester strings for "solar" to get up to speed. I also suggest the Jack Mayer website to understand the practical electrical and mounting details. 300 watts flat mount with mppt is about right to boondocks with MBS. We have 400 watt on pwm and no shortage of power.
Greetings Rich.M ... thanks for the advice. Also you have indirectly answered part of my concern by mentioning you have 400 watts on your roof. How many panels did you install?
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Old 07-08-2016, 05:56 PM   #4
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We have 4 * 100 watt Renogy eclipse panels. They are small in size for their output, high amps ( nearly 6 amps) at a lower voltage of 17.7 made them a better match for pwm controller. 4 panels spreads out well on the roof to minimize shade problems. We have frequently dry camped and had more than enough power. 300 watts would likely be enough if not too many cloudy days.
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Old 07-08-2016, 06:03 PM   #5
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Roof landscape also crowded with wifi ranger and we boost 4gm cell booster on metal ground plane. The Renogy panels work well and are sturdy. We just went thru a hail storm with dime to quarter sized hail without panel damage. Our hengs vent covers have bullet sized holes and cracks after the storm. Duct taped for now as we are 15 days into a 4 week trip.
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Old 07-08-2016, 06:45 PM   #6
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Roof landscape also crowded with wifi ranger and we boost 4gm cell booster on metal ground plane. The Renogy panels work well and are sturdy. We just went thru a hail storm with dime to quarter sized hail without panel damage. Our hengs vent covers have bullet sized holes and cracks after the storm. Duct taped for now as we are 15 days into a 4 week trip.
Rich.M thanks for the photograph ... it says a great deal. It is good to hear that the panels survived the hail. Sorry to hear about your other damage. Interesting, I too am planning to add wifi and cell boosters. I am actually hoping to use one of solar panel as a counterpoise for the cell-booster antenna, and to also shield between the exterior and interior antenna. Since I plan to experiment with an exterior omni-directional and and interior directional, may need a shield to prevent signal feedback. Have you done any experimentation using a solar panel for your ground plane/counterpoise? This scheme, if I can make it work, will allow me to use the booster while in motion and get rid of the so called “candy-bar” antenna which terrible limits the use of your cellphone.
I am also hoping to install the wifi cable such that I can exchange between a whip and a yagi depending on need. I think a yagi with the cell booster is probably unless since calls transmitted between any tower further than 22 miles away will create packet delays greater the 250 microseconds which will begin to drop calls, but I'm not sure about that … haven't kept up on cellphone systems. Beside, a yagi is only useful if parked.
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Old 07-08-2016, 08:14 PM   #7
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I chose to place my booster antenna on a round 3 inch high, 9 inch diameter cake pan painted to match roof as ground plane. This met the criteria for 1/4 wavelength in the cell freq for Verizon lte. 3 inches high was needed to get above the panels. The cake pan is round and seems to maintain the omni directional antenna well in use. I mounted far enough from panel to prevent shading. Even a small shadow may drop panel output. These coaches are small and the cell boosters have internal automatic anti feedback circuits. I went with the candy Bar internal ant but used a low loss cable to run it to the passenger seat visor shelf. Now anyone sitting in passenger seat can call when driving or stopped with boost. If I need to hot spot wifi then we just put iPhone on visor shelf. The coach metal roof keeps cell signal leakage low for max boost at roof ant. It is working well for us. Too complicated to try and shield all areas of such a small coach and I wanted to keep internal ant hidden.
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Old 07-09-2016, 02:16 AM   #8
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I have two 160w panels flat mounted on my roof. In some circumstances the A/C shades one of the panels, which is unfortunate however the overall performance for our needs has been superb. I ran both fans all day, used the interior lighting as much as needed, left portable devices plugged into USB ports to charge and even used the bedroom TV to watch a feature length movie. But the time I went to bed the solar controller was reporting that our capacity was at 85%. By mid morning we were back to 100%.

My controller is a BlueSky 2512ix MPPT controller and I have the BlueSky IPNPro Remote with a battery temp lead and shunt. I also used 6 AWG cable. It's a great system and the remote display gives me an enormous amount of great data.
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Old 07-09-2016, 02:19 AM   #9
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Old 07-09-2016, 09:59 AM   #10
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Greetings dukeboone, thanks for posting those photograph, it is a very clean install. I think a few shadows are unavoidable, as are gray skies. All you can really do is compensate by installing a bit more solar, and try to reduce other losses. I like that you are using 6awg wire versus 8awg. At 320 watts max load the IR drop for 8awg would have been about .12 volt per 10 feet wire run; 6awg is near half at .07 volts per 10 feet. At full load 8awg is producing about 2.2 watts loss per 10 feet; whereas 6awg is about 1.4 watt per 10 feet. While the difference seems insignificant, so also was the cost and labor difference. When designing a system with so many uncontrollable variable, it is good to reduce controllable losses at every practical corner. Given your total wire length is probably two conductors run about 20 feet (40 feet of wire from panel to battery with controller in middle): your 6awg choice is conserving about 25 to 30 watts per day. (forgive me ... I carry an engineering curse from my first career. I can't focus on an entire subject for long, but I can torture an insignificant detail to death.)
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