How to Make a Van De Graff Generator
(An Electrostatic Generator)
There are a number of devices that utilize contact electrification. A popular device is the Van De Graff Generator as it is very simple to construct. This device will produce very high voltage electricity at very low current. This means that they can be safe to touch, although it may make your hair stand on end!
It works by using two rollers and a belt made from dissimilar materials. As the belt rotates, charge separation will continually occur at the point where the belt moves away from each roller. If a metal brush is placed near to these points then the charge can be collected or deposited. The choice of belt and roller materials will determine the polarity of the voltage produced.
A very simple mini Van De Graff Generator can be made from household parts. It wont make your hair stand on end, but it could produce as much as 20,000 Volts. The following parts (or equivalent) can be used for this project.
First of all a pice of PVC pipe or an equivalent insulating support is cut to size. To this the rollers are attatched at each end. The top roller should just spin freely on its axle. The bottom roller should be parralel to the top one and raised up from the base of the support so that is can spin feely and be driven by a motor.
The belt should not be too tight that it creates excess friction as this would be noisy and inefficient. It is common to create a belt driven pulley to link the motor to your bottom roller as this provides a speed reduction and torque increase from the motor. A motor speed controller would also help so that the speed can be adjusted for optimum results.
The wire brushes should be place near to but not touching the roller or belt. It is likley that you will need to experimentally determine the optimum position of the brushes.
The top sphere acts like a capacitor to store energy in the form of displaced charges. Ideally is should be large, round and smooth. Any sharp protrusions on the outside of the sphere will cause corona leakege and prevent a good build up of charge. A single drinks can will work on a small scale and they can even be stacked together for better results.