Step 1: Materials
- Film canisters. You may have to explain to younger makers what film is. ;)
- Magnets. The more powerful the magnets the more powerful the generator will be. I used 1" rare earth ring magnets; they fit very well in the film canisters.
- Magnet wire. This is copper wire coated with a thin enamel. Anything thinner than 25 gauge wire should do and you probably need 10'-15' of wire per generator. Ebay is a good source.
- LEDs. I used 10mm blue LEDs but any normal LEDs should do.
- Thin cardboard, like from a cereal box.
- Tape, preferably electrical tape.
Obligatory safety message: Rare earth magnets are strong and they can painfully pinch fingers. They will snap together astonishingly fast. They are also brittle and will shatter into a thousand little pieces if they snap together from more than a few inches. Kids can't help themselves and will test to see how far apart they can hold the magnets before they attract each other. This will shatter them.
Step 2: Cut and Tape Wire Guides to Canisters
Cut rings out of the cardboard to hold the copper wire in place: draw circles on the cardboard roughly 3"-4" in diameter, then use the canisters to trace a smaller circle in the middle. (You'll need two rings per generator.) Tape them to the canister.
Note about spacing: the generator will work better if the magnets inside the canister can slide completely outside of the rings. See the sophisticated diagram. Position the rings as far apart as you can but still allowing enough room on the ends to allow the magnets to slide outside.
Step 3: Wind Copper Wire Between the Rings
- Try to wind the copper as evenly as possible but minor snags are not a problem. As you can see we had more than a few.
- It doesn't matter which way you wind the copper as long as you do it the same way on the canister.
- Up to a point the more wire you add the more electricity you will generate. There is a complicated formula for determining the optimum length but that's beyond the scope of this project.
When you are done leave another foot-long lead. Tape the two leads to the canister to hold them in place. Use sandpaper to scrape off the enamel on the ends of the wires. (Alternatively you might be able to melt off the enamel with a match but not all enamels can be melted.)
Step 4: Drop the Magnets in the Canister
Drop the magnets into the canister. We used two magnets for each canister because that made them wide enough to keep them from rotating or rolling inside the canister. Put the cover on.
Step 5: Tape the LEDs to Each End of the Copper Wire
You're done! Hold the LED steady in one hand and shake the magnet in the canister back and forth. The rare earth magnets can generate an impressive amount of current.
Some ideas for the next step:
- Add a rectifier to convert the AC to DC so the LED doesn't flicker as much.
- Add a capacitor and resister to store some electricity. This should allow the LED to shine continuously with a constant brightness.
- Add a small rechargeable battery and an on/off switch to make it more like a flashlight.