A while ago, I picked up a solar panel from a Volkswagon dealership when my friend purchased a Volkswagon Jetta. On the way out of the dealership, I peered into one of their closets, and saw a bunch of these panels just sitting in boxes and piled on a shelf. The salesman told me they shipped with the new cars for use during transportation so the batteries would not drain out. They hooked up to the OBD sensor port and mounted on the windshield with suction cups and directly charged the battery from there. Pretty cool, and so was the salesman as he gave me and my friend one panel each.
The panel had been sitting around collecting dust till I scored some replacement UPS batteries (smaller 12v sealed lead acid batteries). But the only thing I could think of doing was cutting off the OBD sensor plug from the panel, and wiring it directly to the battery in order to give it a recharge. It was only until I noticed that our address number sign was missing a bulb and was wired to a small transformer above our water heater, did I begin to dream about a better life for the poor, lonely, solar panel.
Solar panel from nice VW dealership
I work at a computer liquidation company, so finding LEDs was no problem as many computer peripherals, server cases, and the like have these things mounted in/on them. I found three bright white LEDs (I figure they pull about 3.4volts drawing 20 milliamps each after googling), and found an appropriate resistor for use with the system (I used the LED resistance calculator at http://ledcalc.com/), by taking it from an old cisco router powersupply (its actually a 240 ohm resistor and the calculator called for a 100 ohm one, but it doesnt seem to affect it much). I also upgraded my battery to use my old car battery that died from my car…I just charged it for several days with my solar panel till it was 12.7v.
The LED diagram that the LED resistance calculator gave me
As illustrated in the diagram, I wired my LEDs in series, attached the resistor to the positive lead on the LED chain and tested it with my battery. It worked!
Wired up LEDs in series and soldered the resistor to the positive lead
I then unmounted my address number sign and had to pop out the female plug which the bulb would screw into. That gave me a nice sized hole to thread the LED string through.
LED string threaded and secured with some tape and a pluggy thing big enough to cram in the hole where the original plug used to be. In this picture, im using one of the UPS batteries to test it with. Now, I needed to unhook the original wiring which went from the address number sign to the transformer and reroute that with some wire to my car battery/solar panel setup. I went into the garage, and unscrewed the two wires from the transformer.
Transformer with the two wires still connected
I then ran some speaker wire that I had laying around to those two wires to act as an extention, and connected it to my car battery.
Car Battery. You can see the gold speaker wire (connected to existing address sign wiring), and the black wires (connected to solar panel).
I then reconnected the wires from the original address number sign out in the front of my house to the string of LEDs I tested earlier. I remounted (two screws) the address number sign, and replaced the hood which fit over the LEDs.
Address number sign remounted with hood.
I was pleased that it was still working, and waited till dark. I did have to adjust the direction of the LEDs, as they were extremely bright and would streak a beam of light over only certain parts of the sign making it difficult to read. I ended up taking off the hood, lining the inside with tin foil, and oriented the LEDs towards the center of the sign and pointing towards the hood. The tin foil reflected and diffused the light so it was more evenly dispersed.
Address sign at night time.
Im happy with the results, and the idea that I wont be spending any electricity on powering up a stupid address sign at night. It also makes my house easier to spot as the light from the LED is sort of bluish white, and looks completely different from the other houses in my neighborhood.