If you have a bunch of old solar garden lights that don't work so well anymore, and you're thinking about pulling the solar panels off and making something cool with them (since, even if the lights themselves are dying, the panels probably still work), this instructable is for you! This array combines versatility with efficiency; it can produce several different voltages, but without using a power-wasting voltage regulator or boost circuit. It can be made with a few simple parts, tools, and minimal electrical knowledge. The wiring is kind of complicated, so I'll endeavor to explain it as best I can. Post a comment if you have any questions.
Step 1: Materials and Tools
Solar cells; I used nine panels from the tops of solar garden lights; note that I mean only the panels themselves, not the batteries, charging circuits and lamps. Save these for some other awesome project.
Wire; lots of it. I used wire salvaged from two broken strands of incandescent christmas lights.
DIP switches; if you don't know what these are, they're little banks of two-terminal switches, usually used for programming microchips. You'll need about 28 switches for 9 panels, or three banks. Two should be ten-switch banks, one can be an 8-switch bank. You can buy them from many electronics stores for a few bucks, and I guess you could just use a whole bunch of individual two-terminal switches if you can't find any. These are just more convenient.
Wire clamps; the most versatile power output system. You'll need two; red and black makes things easy.
A surface to mount the panels on; I used cardboard. You could use almost anything.
Soldering gun; you'll probably need this to make wiring connections. If you don't have one, good ones can be had for not very much money, and soldering will make your life easier. Trust me.
Step 2: Voltages and Currents
The problem with those panels as they come out of the garden lights is this; they produce 4.5 volts at 55 milliamps. For those who don't know, take my word for it; that's not very much. A single christmas light requires almost 300 milliamps at 4.5 volts! And many devices require more voltage, too. But the nice thing about electricity is, you can connect multiple panels together to get more voltage and more current! But how to do it? Different devices require different amounts of power; just connecting the panels together to have a fixed output will limit what you can power with them. My solution is to use switches to create a fully reconfigurable circuit.
Step 3: Switches and Wiring
Start by attaching your panels to a backing, such as a piece of cardboard. It will help if you number them 1 through 9, to keep track of them later. Find the negative and positive output wires of each cell. there might be a third wire. Ignore it. It goes to the light sensor, which we won't be needing. First, take one of your banks of DIP switches, and connect one wire to all the terminals on one side. It doesn't matter which side; switches have no polarity. Then connect the negative output of cell one to the first switch, the negative output of cell two to the second switch, all the way through cell nine. Lengthen wires as necessary. Now repeat the process with the second bank of switches, and the positive output of each cell. Now it gets a little trickier; take the last bank of switches and attach the positive output of cell one to one terminal of the first switch. Attach the negative output of cell two to the other terminal. Move on to the next switch, and attach the positive output of cell three and the negative output of cell four to its terminals, and so on. The two wires you attached to all the terminals of your first two banks of switches are your output wires. Attack sturdy wires ending in clamps to them. There! That completes your wiring! Sorry if it seems comlplicated and tedious. Drawing a diagram would just be confusing, so I won't. Ask me if you don't understand anything! You'll need to use A LOT of wire.
Step 4: Optional, Auxilliary Stuff
You might want some kind of a handle; I used one from an old briefcase. You'll also probably want some kind of a stand, since the panels work most efficiently when facing the sun as directly as possible. I used part of an old ventilation grating, but many things might work. A useful accessory is a DC extension cord; you can make one by putting color-coded clamps on both ends of a piece of two-conductor wire.
Step 5: Setting Voltages and Powering Stuff
First, determine how much power the device you want to power uses. If it has a DC power port, it should say right on it how much voltage to use. You can also power things that take batteries; just remember that the cylindrical batteries are l.5 volts each (Multiply!), those little box-shaped ones are 9 volts, etc.
The first setting you need to know is this; engage all the switches on the two main output banks, and none of the ones in the bank of eight. (Note that you don't have to use the tenth switch on the two larger banks; just ignore it). Your output is now 4.5 volts at 500 milliamps.
This can power devices rated to that voltage, or close enough, some USB devices, and devices that run on two, three, and sometimes four 1.5 volt batteries.
The next setting is 9 volts. Engage the first switch on the negative output side, skip the next one, engage the one after that, etc, engaging every other switch. Do the same to the bank of eight switches, and on the last bank, skip the first switch, and engage the second, skip the third, and so on. Your output should now be about 9 volts, at 200 milliamps. This is suitable for powering devices that run off 9 volt batteries, 4 to 6 1.5 volt cells, and things with DC ports rated to 9 volts, or close to it.
The final setting is 12 volts. Engage the fist switch on the negative output side, skip the next two, and engage the fourth, then repeat the pattern. On the bank of eight, engage the first two switches, skip the next one, engage the next two, etc. On the positive side, skip the first two, engage the third, skip the next two and so on. When finished, your output power should be 12 volts, at 170 milliamps. You can use this to power some 12 volt devices, and sometimes devices that run on 8 1.5 volt batteries. You could also use it to charge a car battery, or other 12 volt battery cell.
Don't be surprised if a device won't work; it probably just takes more current than the solar panel can supply. It's best at powering radios and other low draw devices. Gameboys, boomboxes, remote controls, and battery chargers are just some of the things I've powered with this! Good luck!