This is a Van de Graaff Generator that I designed and built for use with many electrostatic experiments. I attempted to make a vdg about a year ago, but the design was very poor and the project ultimately failed. I still really wanted to make one though so recently I decided to go back to the drawing board and make a better vdg that would actually work. Because I do not have access to a machine shop for my personal projects I constructed this completely with off the shop parts, and I am happy to say everything fit together quite nicely.
A brief note on safety
A Van de Graaff Generator is capable of generating extremely high voltages, but it is very safe due to the very low current, and quick dissipation of the arcs. For almost all people, the vdg will not adversely affect you in any way (I can't say the same for your sensitive electronics), but if you have a bad heart, it would be a good idea to steer clear of a Van de Graaff generator.
IF you like this instructable, be sure to vote for it in the Make to Learn Youth contest and other contests!
Judges see step 10 for contest information.
A brief note on safety
A Van de Graaff Generator is capable of generating extremely high voltages, but it is very safe due to the very low current, and quick dissipation of the arcs. For almost all people, the vdg will not adversely affect you in any way (I can't say the same for your sensitive electronics), but if you have a bad heart, it would be a good idea to steer clear of a Van de Graaff generator.
IF you like this instructable, be sure to vote for it in the Make to Learn Youth contest and other contests!
Judges see step 10 for contest information.
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Signing UpStep 1: How it works
What good is any project if you don't know any of the theory behind it?
Well it just so happens that the Van de Graaff generator works on a very simple principle. I'm sure you are all familiar with what happens when you walk on carpet with rubber shoes on a very dry day. Your hair stands up, and you are able to send electricity arcing through the air to the dismay of anyone arms reach away from you. This occurs because of something known as triboelectric transfer. When you walk on the carpet the carpet will exchange a charge with you. As you continue walking the charge continues to build until your body does not have the capacity to hold anymore charge, or you get too close to something that has a difference in potential and all the charge suddenly leaks from your body through a path of ionized air.
A Van de graaff generator takes advantage of triboelectric transfer by using a belt on two rollers to carry a charge from a metal comb to another metal comb where the charge gets transferred to a metal sphere.
In construction, the vdg is extremely simple, but the principle that it works on is far more complex. For example, these generators do not have their belt rub on the rollers as rubber shoes do on floors. The triboelectric transfer occurs simply through contact not friction. This does mean however, that the type materials that the vdg belt comes in contact with on the rollers is crucial to opperation. To be effective the materials of the two rollers should be on opposite ends of the triboelectric series, and the belt should be made from a material that falls somewhere in between them in the series. Triboelectric series is nothing more than a list of materials ordered by their triboelectric effect, or the way they exchange charges with other materials. Since the vdg relies on this affect if the two rollers are triboelectrically identical no charge can be built up. In fact, the orientation of the rollers is what determines the polarity of the output. In my case I used teflon for the bottom roller and aluminium for the top so I got a positive output. Swapping the rollers would give me a negative output.
The rollers and belts are only part of the story though. If you look at the diagram above, you can see that two metal combs or brushes are used on the machine. the bottom brush is grounded, and removes the charge from the the top electrode. The top brush transfers the charge from the belt to the top sphere. To better understand what happens with the brushes it would be better to think about an example. Imagine a vdg with a positive output. as the belt comes down from the top roller to the bottom roller, it is carrying electrons from the top brush. As it approaches the bottom brush, the charge is sufficient to ionize the air between the brush and the belt and the electrons move to ground. as the belt continues along, it is triboelectrically charged by the bottom roller to be positive. As it goes across the top roller it begins to pull electrons from the top sphere, leaving unpaired protons, and therefore positively charging the top sphere.
The top sphere of the machine itself is actually highly important to the output of the vdg for many reasons. For example, with the above parameters there is no reason why a vdg couldn't continue building up a charge forever, that is if it wasn't for the fact that for one thing there are only so many unpaired protons that could be left on the sphere, and because any kind of small imperfection or point on the sphere would begin to cause corona discharge, where the charge literally leaks off the sphere and into the air causing a large amount of losses. That being said, The bigger, rounder and smoother the sphere on the top of the vdg, the higher the output it is capable of reaching.
I certainly haven't covered everything, and there is a lot more going on in the operation of vdg's, but hopefully now you understand the basics of how they work.
Well it just so happens that the Van de Graaff generator works on a very simple principle. I'm sure you are all familiar with what happens when you walk on carpet with rubber shoes on a very dry day. Your hair stands up, and you are able to send electricity arcing through the air to the dismay of anyone arms reach away from you. This occurs because of something known as triboelectric transfer. When you walk on the carpet the carpet will exchange a charge with you. As you continue walking the charge continues to build until your body does not have the capacity to hold anymore charge, or you get too close to something that has a difference in potential and all the charge suddenly leaks from your body through a path of ionized air.
A Van de graaff generator takes advantage of triboelectric transfer by using a belt on two rollers to carry a charge from a metal comb to another metal comb where the charge gets transferred to a metal sphere.
In construction, the vdg is extremely simple, but the principle that it works on is far more complex. For example, these generators do not have their belt rub on the rollers as rubber shoes do on floors. The triboelectric transfer occurs simply through contact not friction. This does mean however, that the type materials that the vdg belt comes in contact with on the rollers is crucial to opperation. To be effective the materials of the two rollers should be on opposite ends of the triboelectric series, and the belt should be made from a material that falls somewhere in between them in the series. Triboelectric series is nothing more than a list of materials ordered by their triboelectric effect, or the way they exchange charges with other materials. Since the vdg relies on this affect if the two rollers are triboelectrically identical no charge can be built up. In fact, the orientation of the rollers is what determines the polarity of the output. In my case I used teflon for the bottom roller and aluminium for the top so I got a positive output. Swapping the rollers would give me a negative output.
The rollers and belts are only part of the story though. If you look at the diagram above, you can see that two metal combs or brushes are used on the machine. the bottom brush is grounded, and removes the charge from the the top electrode. The top brush transfers the charge from the belt to the top sphere. To better understand what happens with the brushes it would be better to think about an example. Imagine a vdg with a positive output. as the belt comes down from the top roller to the bottom roller, it is carrying electrons from the top brush. As it approaches the bottom brush, the charge is sufficient to ionize the air between the brush and the belt and the electrons move to ground. as the belt continues along, it is triboelectrically charged by the bottom roller to be positive. As it goes across the top roller it begins to pull electrons from the top sphere, leaving unpaired protons, and therefore positively charging the top sphere.
The top sphere of the machine itself is actually highly important to the output of the vdg for many reasons. For example, with the above parameters there is no reason why a vdg couldn't continue building up a charge forever, that is if it wasn't for the fact that for one thing there are only so many unpaired protons that could be left on the sphere, and because any kind of small imperfection or point on the sphere would begin to cause corona discharge, where the charge literally leaks off the sphere and into the air causing a large amount of losses. That being said, The bigger, rounder and smoother the sphere on the top of the vdg, the higher the output it is capable of reaching.
I certainly haven't covered everything, and there is a lot more going on in the operation of vdg's, but hopefully now you understand the basics of how they work.
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2. I keep hearing that the proper distance from comb to belt/roller ranges anywhere from 1/4 of an inch, to 3/8 of an inch, or 1/8 of an inch and so on. Can you please clarify for me what is the proper distance?
2. how important is the "no dust" on the parts?
3. If my project works will I get a big or small shock?
2. If you're talking about the metal stuff from your last comment, pretty important. If you are talking about dust in general, it will hurt your performance but it won't be drastic.
3. You will get a decent shock but it will do absolutely nothing other than cause very mild pain.
2. I was thinking about attaching my top wire to the sphere with duct tape. Is this ok I heard that duct tape has some metallic properties. Also do I put the tape on the bare copper wire, or off it?
3. I heard the the bigger the sphere the longer the pipe has to be. Is that true?
2. As long as there is bare copper in contact with the inside of your sphere it will be fine
3. Not necessarily. To an extent it is true. If you have a very large sphere you are going to want a larger pipe to support it and keep it away from ground, and as your output gets higher you will want the terminal further from ground, but for most cases so long as the pipe can support your sphere, and keep it a decent distance from ground it will be fine.
Well done you.
Another question: ¿how many minutes it works before accumulate an interesting charge? I think would be a good idea replacing the motor by a handle, to eliminate the idea of electricity transfer.
1. how big does the hole in the sphere have to be?
2. How did you make your discharge wand?
3. How did you get the coat hanger to bend the right way?
4. I was thinking about making a support for the sphere on the pipe. Any suggestions?
5. I was also thinking about putting nylon treaded nuts on the outside of my top roller. Will this effect the ability to discharge?
1. how much of the top roller has to be in the sphere
2. for the bottom bruch heres what I am thinking about doing:
I bring the wire from a hole I drilled in a PVC tee a bit a above the bottom roller. I then pull the wire downwards, then I bend the wire a bit upwards then make an "L" shape at the bottom of the roller where the tips of the of the brush are a bit below the bottom. Will this work?
3. For my top roller I was thinking about doing the same thing. Does it matter if I have a lot of PVC pipe in the sphere, also for my top wire going to the sphere does it matter how long the wire is?
2. that would work fine
3. No and no.
1. do the brushes have to be pointing up towards the roller
2. also when I am doing my grounding would a srcew work?
1. I am powering the botton roller with an impact drill and socketfitting. the bottom brush wire I thought I could connect to a plug (just a wire to the ground part of a 3 prong plug), and I was hoping to attach the wire from the bottom roller and the wire form the plug to a screw (like a common point to ground I think its called).
2. And also how did you get your sphere from sideing down the pipe I am stumped.
2. I bent part of a coat hanger (the wire kind) into a V shape and put in two holes I drilled at the top of the PVC. The sphere was able to sit on top of that.