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KCA Science Club "Van De Graaff"

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This is a simple Van De Graaff generator.  We used a 6-inch piece of plastic pipe 30 inches long; an oscillating fan motor bolted directly to bottom of pipe which had a nice long shaft where a plastic bed roller was driven into it tightly.  Another plastic bed roller bolted to the top with 1/4 40 thread all.  This allows you to bolt it to the pipe as well as using nuts to keep the roller in the center.  Be sure to place your metal bowl down the middle of the pipe first before going to the trouble of bolting the top.  We cut the 6-inch hole out of the salad bowl with a dremel tool and a hack saw blade held by hand.  We bought some heavy gauge insulated wire, then stripped the plastic coating off and fanned out the wire to pick up the charges off the rollers.  Make sure you snip the wires so that they lay evenly along the  roller.  We had to watch closely at first to make sure the belts did not catch the wires if too close.  We used some angles off of an erector set to help hold the wires tightly.  We made belts from exercise rubber bands; vinyl-covered shelf paper with a felt backing; neoprene cloth-backed materials used to support backs for sports, as our test belts.  The shelf paper worked the best and was pretty cheap.  It's a simple, fast construction that we hope to improve.  One of the problems is that the belts if too tight make the fan motor hard to turn.  We use a drill motor to the shaft sticking out the opposite side of the pipe to get the belt a little loose so the fan motor will turn it.  We have had high humidity so far during our experiments but even still have had 10 cm charges.  The bottom roller is covered with aluminum tape and the top one with plumbers' pipe-fitting tape (teflon maybe.) 
pfred21 year ago
Getting the right motor for your generator is going to be tough. You need a small motor with high starting torque. The motors in fans are a good size, but the wrong type to deliver any starting push. You may have to accept that you have to jump start your generator in order to get it going. I'd put a tire on the shaft, then have another tire I could chuck into the drill to friction drive start it. Easy on, easy off.

Ideally you should have a small capacitor start induction motor. But where you can get one of those I've no idea. I know where there are lots of them, but I'm not sure you can practically get to them yourself. Find a contractor that does heating and cooling and ask them if they have some little scrap motor you can have. They might have just the thing. If they don't then no one does. As soon as you say belt to the HVAC man he'll know exactly what you need. His business is to know which motors are suitable for fans, and belt driven machinery. He lives, eats, and sleeps the stuff!

If he is a really good guy he'll go out to his shop and cut one off a little compressor for you. It'll be just the thing too.
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