DIY 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.
Large rubber band
Large glass fuse
Small metal rod, or a nail
Plastic pipe (~4cm diameter)
Insulation tape
Small motor & batteries
Empty drinks can
Wire
You can buy Van de graff generator parts or even a ready made one from our shop. Check out the Science Lab for Van De Graff Generators, rollers, belts, metal spheres, and more great items.
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.
The information provided here can not be guaranteed as accurate or correct. Always check with an alternate source before following any suggestions made here.
Thanks,
Marc
This is about as small as it can be made whilst still being able to accumulate enough charge. The contacting surface area of the belt determines the charging rate. The size of the metal can determined the amount of charge that can be stored on its surface.
Rubber is a common choice, but it must not be the black rubber you often find used as drive belts as this contains carbon.
Drive belts are often round, but ideally the belt should be flat. With more surface area in contact with the rollers it will perform better.
Now you have a working van de graff generator you can do experiments like franklins bells
im making a much bigger one about 130cm tall but need to know if this material would be suitable for a VDG belt i would think so but im not sure.
james if you need help try my web site but youll find better quality information on RMC's
www.justinlaird.piczo.com you might have to search a bit
The support can be any shape and it does not need to enclose the belt. It just needs to be a good electrical insulator which can be used to support the top sphere and roller assembly.
Anything insulating (usually some sort of plastic) will do the trick. You could even build one from a tower of lego.
a good ve- would be electrical tape, teflon and pipe seller tape the good ve + im not so sure.
have you noticed that the spark produced is much like a fly back transformer it starts glowing purple then sprays till a big arc froms
This drawing shows how the masts of the ship act like sharp points on a charged sphere (earth) causing the surrounding air to be ionized.
i finaly got 2 inches of spark with my mini vdg which for its size is pretty good.
i would take a photo but it lasts only for 1000th of a second. i used a lightning rod ball thingy.
im making a bigger vdg and used your advise as posted in the previous responces about lakering wood. i also added electric insulation tape.
p.s i got some materials and im building my generator and justin i did check out your page lol.
dose it look like im on the right track? i put tape around the edges to prevent cornial discharge as you explained befor
This is because all the like charges are trying to get as far from eachother as possible. When they are able to move (on a metal object), the charge will distrubute its self around the outermost surface. If the wire from the brush is sticking out of this sphere, charge will be trying to get back away from the sphere as this wire is the outermost conductive point. This will leave your top brush fighting to add more charge to the sphere. If the brush and roller are inside the sphere, the charge will be heading straight to the outer surface of it. The only things sticking out of the metal sphere will be the support and the belt which are both non conductive.
also i will add a glass roller at the top from an old V drink bottle for extra power.
if i was to add a inclosed structure around the belt, would that prevent humidity?
the belt will be made of black durable plastic found in all good hardware stores.
I was gonna use glass but someone said it was to be avoided due to temperature change and humidity, can you help? p.s This is only for a small generator 12 inches tall.
Obviusly this list only has a few materials on it so google around to find the positions of other materials in the triboelectric series.
The issue you mention for glass is just due to its relativley high (compared to low density materials like plastic) specific heat capacity. You might get the same condesation effect as you would with any glass or window that has a lower or different temperature to its surroudings.
If your VDG is just in a house then you are unlikley to have any condesation problems. It may only become an issue if you took it out into the cold for a while and then brought it indoors. The cold glass would then cause moisture in the air to condense onto the roller. The same would occur for any metal parts, but the temperature of these will equalize more quickly.
I feel that since, it is farther away on the triboelectric series, it would produce a better voltage. And how much time would it need for a rubber band based VDG to produce a spark of an inch? Will it be a sufficient earth connection if I touch it barefoot? Will I get an electric shock? Sorry for the hail of questions.
The time taken to charge and the length of spark depends on a lot of factors.
The bigger the topload (metal sphere) the longer the spark can be.
The width and speed of your belt will alter how fast it can charge up. Wider is better as there is more contacting surface.
The atmospheric humidity can also have an adverse effect. The air needs to be quite dry for good performance.
You don't need to be barefoot. It will still zap you as charge will soon leak from your body into the air or through your shoes.
First of all I was wondering what constitutes the voltage output of a vdg? Is it related to belt lenght?
I am using a glass tube for a top roller with ball bearings istalled in each end, and was wondering if ptfe (Poly Tetraflouro ethylene)
is good for a bottom roller? Also with these materials for rollers I was thinking about latex rubber for the belt, is this a good idea? What is the best material for the belt?
Thanks alot for the help.
PTFE and latex should be fine. The triboelectric series is what you should check.
Also maybe I am a little mixed up, I thought that the sphere was just to act as a capacitor, thus the larger the sphere the more current stored and the more power available. Also if the sphere controls the voltage than what id the purpose of building a 5' tall vdg, why not build it smaller like 2'.
Also if the wider the belt the faster the charge time, what does the height of a VDG determine, is a longer belt better?
The height is used to isolate the high voltage parts from ground. If it is too low, the high voltage would just leak through the air back to earth. Building this device, like building any device is about finding a compromise between the optimum physics, and what is actually practical.
You can power an electrostatic motor with them.