Cole-Parmer Blog

October 2009 marks the 80th anniversary of the Van de Graaff electrostatic generator. While this machine is widely recognized for its loud sparks and hair-lifting demonstrations, more importantly it represents a significant benchmark in the production of static electricity at high voltages.

Dr. Robert J. Van de Graaff developed the electrostatic generator in 1929 while he was a research fellow at Princeton University. He moved to the Massachusetts Institute of Technology where, between the years of 1931 and 1933, he crafted a larger generator that produced significantly higher voltages. While at MIT, he developed the world’s largest Van de Graaff generator which is currently displayed at the Boston Museum of Science.

The Van de Graaff generator is sometimes mistaken for the Tesla coil because of similarities in appearance. However, Nikola Tesla’s invention—which predates the Van de Graaff generator by nearly 40 years—has a completely different function. The Van de Graaff generator creates static electricity, while the Tesla coil creates high-voltage current electricity that is transferrable through the air into other objects (e.g. a light bulb). Nevertheless, Tesla recognized the generator’s potential in the 1934 article titled “Possibilities of Electrostatic Generators,” when he referred to the Van de Graaff generator as a “remarkable device,” agreeing with the assertion “with which wonders will be achieved.” †

Tesla’s statement would prove to be correct. Because of its use of a power supply to a produce continuous static electricity, the Van de Graaff generator quickly eclipsed previous electrostatic models.

Basic principles of the Van de Graaff generator

They come in many sizes, but each Van de Graaff generator is comprised of three central components: the terminal, a belt and pulley system, and a motor. The terminal is the insulated hollow metal sphere elevated at the highest point of the machine where the current is expelled.

The belt and pulley system features an insulating belt which transfers charges to the terminal. The belt creates static through friction with a metal electrode, also known as a needle or comb. There are two pulleys—each with a corresponding electrode—in place: one at the bottom of the machine, connected to the motor, and another positioned within the base of the terminal. One side of the belt carries a positive charge, while the opposite carries a negative charge. Both pulleys are contained in a hollow cylinder that is connected to the sphere.

Lastly, at the base, a switch-operated motor powers the generator.

The mother of all science fair projects

Constructing your own Van de Graaff can be a fairly straightforward process. Moreover, it is a safe, cheap, and fun way to demonstrate the properties of static electricity. To commemorate the Van de Graaff generator’s 80th birthday—and to help you stay on the cutting edge of the 20th century—here are few pointers to consider when building your generator:

1. The most crucial part of the generator is the terminal. As such, to achieve the greatest charge, you should only use a round hollow sphere made of stainless-steel or aluminum. To test the effectiveness of the generator, you can place a negatively charged metal object close to sphere to make a spark. Even more illustrative, place your hands on the sphere and in an instant the hairs on your head will stand up.
2. The belt is also very important. To create the most static, use a belt made of vinyl or silk. Be sure that the belt is bound tightly to the pulleys so it is unable to move laterally. (Also, bear in mind, the belt and terminal are the most difficult pieces to replace.)
3. To ensure your machine stays intact, use a strong adhesive to firmly attach the metal sphere to cylinder—PVC piping is highly recommended—surrounding the belt.
4. The electrodes are also pivotal in the performance of your generator. For both pulleys, position the ends of electrodes close to the belt without touching it.
5. Lastly, make sure your surrounding conditions are not damp or humid. The generator may not work in such conditions.