Build Your Own!
If you are mechanically adept, it is easy to build your own Van de Graaff generator from scratch (if not, you may wish to buy a kit or a finished generator -- see the links at the end of this article for some ideas). The following is a list of the parts and materials I used to build my Van de Graaff generator.
- Motor - I bought a used, 1/3 horsepower, 1,780-rpm motor from a local motor repair shop.
- Belt - I used a piece of surgical tubing. DO NOT USE BLACK RUBBER! The belt must be an insulator.
- Lower roller - I used a piece of nylon, 3 inches in diameter and 3 inches long, with a crown in the middle. The roller was drilled to accept a 5/8-inch motor shaft with key and covered with silicon tape (available at a hardware store or online at McMaster-Carr -- use 1" wide and 20 mm thick).
- Upper roller - I used a piece of nylon, 2 inches in diameter and 2 inches long, with a crown in the middle.
- Upper and lower brush - I used two pieces of multistranded, braided grounding straps.
- Sphere - I used two stainless steel salad bowls resting rim to rim.
Rollers. I would advise any serious builder to use the negative-roller/positive-roller technique. The results are much better than having one roller neutral. Get an idea of what materials you want to use and then go search the local hardware stores. There are many materials on the triboelectric list that can be found with slight to moderate searching. Avoid using aluminum foil or any other metal that can tear or flake. If the aluminum flakes, it will get on the belt, thus shorting out the Van de Graaff generator. You should try to put a crown in the rollers (make the middle bulge out like a keg). The crown will cause the belt to track the middle of the roller, thus eliminating the potential for the belt to slip off.
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Belt. The surgical tubing that I use performs flawlessly. It's extremely durable, easy to keep clean (wipe with rubbing alcohol), and easy to work with. Purchase the tubing at a good hardware store or a medical supply store. You will then need to cut the tubing to make a flat strip. Do this with scissors or by inflating the tubing. To form a belt, form the strip into a circle and overlap the ends slightly. Cut a 45-degree angle through the overlapped portion (cut all the way through). Now butt the two ends together and bond them with rubber glue. The 45-degree seam will help the belt to travel over the rollers when the seam reaches them.
Remember that the belt must not be conductive. Avoid using any material that is black -- it probably contains carbon, which is conductive at the high voltages a Van de Graaff generator develops. The belt width should be as close to the roller width as possible. You want to ensure that the brush is "coating" the belt and not losing charge to the roller.
Brushes. The brushes must be a conductive material such as metal. I've found that the smaller and the sharper the brush tips, the better the performance. Try placing the brushes at various distances to the rollers. Do not allow the brushes to contact the belt. This will cause debris to build up and will ruin your belt. Unbraiding the fine wires in grounding strap wire works well and is recommended.
Motor. The motor is arguably the least critical aspect of the Van de Graaff generator. Obviously, you want one with enough horsepower to drive the belt. Try looking at local motor repair shops. I even used a circular-saw motor at one point. For the motor speed, I would not use anything less than 1,000 rpm. The speed determines how fast a Van de Graaff generator charges up (do not confuse this with how much charge is built up).
Sphere. Any hollow metallic sphere will work fine. The two salad bowls that I use had some leakage where the rims came together. I remedied this by sealing the seam with epoxy and covering it with electrical tape.