Van De Graaff Generators & High Voltage Stuff

How does it work?

High Voltage Links Page Here

20 inch sparks from a homemade Van de Graaff generator! The metal sphere on the right hand side of the picture is 19 inches in diameter and is the top terminal of my MK3 Van De Graaff generator.

What is it? The Van de Graaff Generator is an electrostatic generator capable of generating extremely high voltages upto around 20 million volts. Named after its inventor Robert Jemison Van de Graaff, who was a professor at MIT. The Van de Graaff Generator was developed around 1929 to 1931 to supply the high energies required for particle accelerators of that period. His prototype machine stood around 6 feet tall and was capable of generating around 1 million volts.

Details on my MK4 VDG coming soon. Watch this space.

What is in it? The classic Van de Graaff Generator or VDG contains no power supply other than the power used for the drive motor. Some smaller versions though are hand cranked and have no electrical power supply at all. If we examine the component parts of the VDG it appears to be deceptively simple. There are two rollers, an upper and a lower. In contact with both rollers is a rubber belt. The lower roller is directly driven by an electric motor. There are also two combs one in proximity to each roller, which serve to collect the charges. The top terminal or sphere serves as a capacitor on which the accumulated charges gather. On the left is a picture of my MK3 VDG machine. It stands just over 4 feet tall or 1.29 metres if you prefer. The lower roller is made from solid PTFE stock and the upper roller is solid aluminium. The belt is of 2 inch (50mm) wide rubberised webbing. The support column is made of acrylic strip approx. 4 inches (100mm) wide by inch (6.3mm) thick. 3 of these strips are glued together to form a ‘U’ shaped structure. The top terminal or sphere is made of aluminium. The drive motor is a universal a.c. motor salvaged from a scrap piece of equipment. When conditions are good with low humidity, this machine is capable of generating sparks around 20 inches in length! So what voltage does this equate to?

See the Bit Of Theory section for more info.

How do we measure high voltages?

Here are a few more pictures of various parts of the VDG along with more details of the manufacture and construction methods.

This is a view of the lower roller. The roller is made of solid PTFE stock. In the lower part of the picture can be seen the lower charge comb made of steel needles soldered to a piece of copper clad pcb. The lower comb is electrically connected to mains earth.

The view left shows the upper aluminium roller of similar dimensions to the lower roller. The roller runs in bearings and the side mounts are adjustable for belt tensioning. The upper comb can also be seen just above the belt and roller. The connecting wire between the comb and the top electrode can also be seen.
Here the drive motor and belt drive can be clearly seen The toothed belt and pulleys gives a speed increase of 1.5 : 1. The motor rotational speed is 2780 rpm. The motor then drives the lower roller via a toothed belt and pulley system that results in the lower roller being driven at approx. 4170 rpm. These materials used here are not necessarily the best, in fact I am still working on improving the performance. However, the performance obtained using these materials is very good and an excellent starting point for anyone interested in trying their hand at building a VDG generator.

Last update 10/02/03