This is an update of a project I did about 10 years ago, before I had a 3D printer. The original project is detailed here. It used rollers made from PVC pipe that turned on skate wheel bearings, and was driven by an AC motor. This new design uses a 3D printed base and rollers, spinning on bearings harvested from hard disk drives, and is driven by a small DC motor. Though the motor turns at about the same speed, it runs quieter and charges faster because it uses a wider belt. The new design makes belt replacement easier.

It uses a pair of steel, Blanda salad bowls from Ikea for the top electrode. Their 11" (280 mm) diameter means the generator can charge up to 400 kV under good conditions (low humidity air), and throw thick, blue, painful sparks about 300 mm long every few seconds.

Here it is in operation, on a damp, rainy evening, in slo-mo:

And not so slo-mo:

When you are handling the parts and assembling them, be sure your hands are clean or wear gloves. Clean the pipe inside and out with warm water and dish detergent and rinse thoroughly and dry it. A little contamination in the wrong place can reduce the output of your generator.

How does it work?

VDGs operate on the principle of triboelectricity. When objects made of dissimilar materials are brought into contact, a weak chemical bond is formed through sharing of electrons. When the objects are separated, one of them ends up with more electrons than the other and the two objects are said to be charged. In this machine, the rubber belt picks up electrons from the aluminum and transports them to the metal sphere at the top of the machine. At the other end, the Teflon pulls electrons from the belt and sends it back down the column, positively charged, to the brush at the bottom of the machine.

Moving electrons, whether they are moving in a wire or being physically transported on a rubber belt, constitute an electrical current. The sphere at the top of the column forms a capacitor with the Earth. The moving charge accumulates on the sphere, charging that capacitor (opposite charges are moving in the ground at the same time they are moving in the machine). As the charge on the sphere accumulates, the voltage (by definition, the physical separation of charges) rises. The faster the belt moves, the higher the current. The wider the belt is, the more room is has to carry charge, so the higher the current.

Air can support a limited electric field before it ionizes and becomes an electrical conductor. That electric field limit depends on the temperature and humidity of the air. More humid air breaks down at lower electric field strength. Dry air can withstand higher fields/voltage before the air ionizes.

The diameter of the sphere and the charge it accumulates determines the voltage on and electric field intensity around the sphere. As charge accumulates on the sphere, it spreads out over its surface. The electric field will be most intense at sharp points (such as the sharp edge where we cut a hole in the bowl, hence the plastic tubing to insulate that sharp edge), so the air will tend to ionize at a point at a lower voltage than it will at a large smooth surface. The larger and smoother the surface, the lower the electric field intensity, so it is ultimately the diameter of the sphere that determines how high the voltage can get on the sphere before the surrounding air ionizes and leaks away the charge. At some voltage, the charge leaking off into the air will equal the charge coming up the column and the voltage between the sphere and ground will stabilize... until you get near it and provide a path for a rapid discharge of the capacitor.

Note: you may see some minor differences between the parts in the CAD file and the photos. After the photos were made I made some minor changes to the design to make assembly easier and to improve operation.

Let's get started...