Power from the Sun!

posted in: Techie Posts, Uncategorized | 1

We (RVers) all dream of unlimited power. Power to boondock anywhere, to live far from the nearest extension cord. Our motorhome came with 4 golf cart batteries and a 2000 watt inverter that can run nearly everything, for a while. To charge those batteries, we can use our generator, but wouldn’t it be nice not to have to?

Most people talk of energy audits, and “how much power do I need?” Not me. My onboard charger is 100 amps. I did some math, and just don’t have the roof real estate for that. I did some measuring, and a bunch of shopping on ebay, and found some US Made 150 watt panels. 58 by 26 inches fit right in. They are 8 amps at 18 volts. 4 fit nice in the space I had, and left enough room to walk and work on the roof, and wouldn’t fall in any shadows.

I decided to go with an MPPT chargeoutback_flexmax_60 controller. These use digital technology to maximize the power from the panels, and they are made to take in a higher voltage and step it down to the right level for the batteries. I selected Outback as my vendor, and purchased their 60 amp controller. With the MPPT controller, I decided to wire my panels in “series pairs”. Each pair of panels produces up to 36 volts. This will work great in low light, and give the controller a lot of excess voltage to work with.

BracketsI did a lot of reading at amsolar.com,panels_with_brackets and one of the things I “borrowed” from them is the mounting setup. I used nutserts in the ends of the panels to take a 1/4-20 bolt directly. Then I made my own brackets out of alluminum. I used 3M trim tape and a few #8 screws to secure the panels to the roof. The 3M tape will hold them, the screws just made me feel better. The design of the brackets will make it simple to add tilt bars when I feel the need.

roof_wiringWiring is vital for these things,junction_box and bigger is better. I went to our local high end car stereo shop, and bought a bunch of 8 gauge black and red wire for panel to panel, and 4 gauge to run from the roof junction box four_donedown to the charge controller. I used a 4″ waterproof plastic electrical box from home depot and some bus strips as my power junction on the roof, and screwed it down directly over where the cables would penetrate the roof. The panels came with industry standard MC4 connectors, I bought matching MC4’s on ebay, and wired it all up, soldering every connection.

Closet_wiringMy studying found a false back in the cabinet in the bathroom. This cabinet was setup for a washer/dryer option that we didn’t have. Easy enough to pull out the shelves, pop off the false back, and there was all our plumbing, including the main vent going up through the roof. I put the junction box on the roof a few inches from the vent, double and triple check, and drilled a couple holes. I fed the 4 gauge wire down along the vent pipe, down into the tank area, then over and back to the charge controller, which I mounted in the same bay as the inverter, right behind the batteries.

plus_twoThe first few tests, it worked great, but was only giving me about 35 amps (only…. haha) So heck, I bought 2 more panels, made some more brackets, bought some more wire, and hooked them into the junction box.

Then some real tests. I ran the batteries down. And monitored on a bright sunny day. This maxed out the controller at 60 amps. Nice.

We’re now ready to go boondocking!! Our next stop will be the Arizona desert, to give our new setup a real test!

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One Response

  1. That is super duper great for you guys! Looks like Jim’s thinking, buying and assembling is really going to work well for you. Good job!! Loved seeing the photos and detailed description from start to finish. 🙂

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