Designs on the Sun Therese Peffer c. 1993 Therese Peffer Sometimes things turn out great without any planning! We hadn't seen the sun in several days, but as soon as I had made a bit of progress on my system, we had five glorious blue-sky sunny days. The planning and design of a renewable energy system, however, takes a bit of time, but is well worth every minute. Several months ago, I bought a 60 Watt photovoltaic panel and got a frame for it. I bought 60 feet of #10 wire with USE insulation (this insulation resists degradation by sunlight and can be used outdoors). A friend gave me a car battery from a dead SAAB, so I hooked the two together and charged the battery just for fun. That's what got me started. It sounds so simple doesn't it? Just "hook the two together." Since then I've spent many hours thinking and rethinking my little system for my trailer. I've looked at other systems in Home Power for ideas. I've drawn countless sketches, both electrical schematics and physical diagrams. One of my "hurdles" was learning how to use a wiring diagram. I had a difficult time translating the electrical lines and squiggly representations to how things were physically connected. I was much more comfortable drawing the system as I saw it, with all the fuses, plugs, wires, and connectors. Simple Connections So I started from a very simple concept: my PV panel connected to my battery (see diagram). The panel sits about 20 feet from the trailer, so allowing for slack I cut two 25 foot lengths of the wire. The Solarex panel requires spade connectors (the connectors are shaped like a U or fork), so I added spade connectors to the ends of the wires. I crimped and soldered all connections. Solder increases the contact of the metal connector to the wire and reduces resistance. There's a lot of connections in my circuit! If there is a poor electrical connection (resistance) at any one of the junctions, this affects the whole circuit. The resistance of the whole circuit will affect how much of the electricity gets to the battery and appliances. First, I stripped the ends of both wires about an inch with a pocketknife Ä USE insulation is no match for wire strippers! Next I crimped the spade connectors to make a good mechanical connection and soldered the connector to the wire to ensure a good electrical connection (see photo). The car battery had round posts Ä too large to accept ring connectors. I bought wing nut battery terminals at an auto parts store. The terminal fits around the battery post and has a 5/16 inch bolt. I connected the appropriate sized ring connectors to the other ends of the wire, tightened the wing nuts, and charged away! One immediate problem arose Ä I couldn't leave the system alone for very long. I was constantly heading down to my simple setup with the voltmeter to check on the battery. I sure didn't want to overcharge the battery! Controlling the Charge I took a look at Chris Greacen's portable system (described in HP #28), and borrowed a few ideas. One step was to add a regulator which would prevent the panel from overcharging the battery. (Of course this would free up my time, too!) I liked the idea of having the "brains" of the system arranged neatly in a box. I didn't want to cut or drill holes in the inside wall of the trailer, so a box seemed to make sense. There's a shelf just above the seat under which the battery lies Ä just the place for a small (9 inch by 14 inch by 7 inch tall) plywood box. I "homebrewed" (built) a regulator like Chris' (see HP#28 for details), my first homebrew experience. It's not a neat, pretty regulator Ä the metal box which holds the perforated board and wires barely closes Ä but it does work! So now the wiring diagram looks like this: Not the whole picture But the wiring diagram doesn't show everything! I decided to put a plug on the PV panel so I could disconnect it for travelling or maintenance. I bought a plug from Radio Shack. More soldering! I'd use a different plug next time Ä I had to use a piece of sheet metal to attach the female end of the plug to the plywood box. A lightswitch outlet plate makes a neat cover hiding my metal work mistakes. As far as I know there is no set standard polarization for this plug. One side was angled which I designated positive. The diagram also does not show how the regulator is wired. I didn't want to "hard wire" the regulator into the system Ä I want to be able to remove it or replace it without too much trouble. I used a barrier strip to accomplish this. A barrier strip allows the electrical connection of two ring connectors. A small plate of metal holds two screws, one for each ring connector. Since there are four wires attached to the regulator Ä positive and negative from the panel and positive and negative going to the battery Ä I needed an eight terminal barrier strip. The convenience of removing the regulator cost me a bit of soldering. There were eight ring connectors total! I arranged the barrier strip on the same side of the plywood box as the panel plug. The next step was safety! After looking at a few systems, I decided to put a fuse between the panel and the regulator and one between the regulator and the battery. I bought two fuseholders at Radio Shack, mounted them in the box, and put two 20 Amp Littlefuse fuses in them. This will protect the regulator against any surges in current. After a bit of soldering, I was set. Now the wiring diagram looked like this: Lights and Music Now the point of all this is to produce electricity for a 12 Volt light and my radio/tape player. I started thinking about outlets and plugs. I could use a cigarette lighter plug for the radio/tape player Ä it doesn't draw that much power (22 Watts max, or less than 2 Amps at 12 Volts draw). I bought a Suntronics brass outlet rated at 20 Amps. I've seen cigarette lighter outlets/plugs are rated for 2 to 20 Amps, which makes me wonder how hardy the connection is. For the light, I was more concerned about a good solid connection. I wanted to experiment with different types of 12 Volt lights: compact fluorescent, fluorescent, and halogen lights. Some of these lights draw up to 50 Watts, so I thought something more heavy duty than a cigarette lighter plug was in order. At our "local" hardware store, I found a plug and outlet rated 20 Amps/250 Volt, which is more heavy duty than I need, but better safe than sorry! The plug has three prongs; the two flat prongs are not parallel like a regular 110 vac plug, but are at right angles to each other. I could have used a regular 110 vac plug and just wired it for DC, but I felt that was asking for trouble. I wanted to make sure that only 12 Volt appliances could be plugged into my socket. I bought plastic outlet boxes and started sawing holes in plywood. Electricity from the battery The next struggle was a design problem. I needed to get electricity to the battery from the panel and I needed to get electricity from the battery for the loads. The wiring diagram helped here: I could use two wires from my box to the battery and two more wires from the battery to the box Ä four wires total. But by looking at the electrical diagram I discovered that instead of using four wires, I could use two! Two conductors make for a much neater and simpler system. Plus, the location of the posts inside my box will make it easy to tap leads to a future ammeter and voltmeter. I put two 2 inch long 5/16 inch bolts through the side of my plywood box. I arranged the "posts" vertically instead of horizontally as a safety measure Ä less chance of a wrench falling across the two posts sparking a huge short circuit current from the battery. I soldered ring connectors to wires leading to the battery and to wires leading from the regulator. Time to stack up ring connectors! One stroke of luck was finding a four foot piece of #8 gauge 3- ply extension cord for a dollar at the hardware store! The size and flexibility of the extension cord were perfect for getting electricity in and out of the battery, although I don't need the third wire. Plus, my two wires look like one Ä no tangled wire Ä and the conductors are well protected with two layers of insulation. The best laid plans... The trailer system is almost ready to unplug from Home Power Office & Power. But, I've already found changes to make! I will add disconnects between the battery and my outlets and think about other safety features. I just bought some surplus airplane meters and plan to get an ammeter and voltmeter on line soon. Then I'll add a handle to the box, and maybe a plexiglass lid. It's been overcast here lately Ä I better get to work! Access Therese Peffer, Home Power, POB 520, Ashland, OR 97520 ù 916-475-3179