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.

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Step 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.

<p>Can you please tell me where you got your motor from, what kind and size (HP? Voltage?). Also , where is the best place to get the belt....i am making this for my science fair project so thanks for your help!</p>
<p>we r doing this for our school science exhibition and i need hep and its the day after tomorrow , tell me where the connections from the brushs lead to, if any pictures of that is there it would hav been really helpful for us ...</p><p>thanx....</p>
<p>Sorry this may be a bit late now. The top brush connects to the metal sphere on the top, and the bottom brush connects to mains ground (or another good earth ground, e.g. a water pipe, sink tap, metal rod pounded a couple feet into the ground, etc.)</p>
<p>Instead of spending $20 on a latex belt, why not just make a belt out of a latex condom?</p>
<p>Hey I almost made the whole thing but I have a doubt about the dome. I got something that looks just like a smooth round earthen pot, but it is made of steel. I think it will work nice because it is about 12'' in diameter but the thing is that its 6 inch mouth is way too bigger than the 3'' PVC, so if I did fix it on the VDG it will be for all purposes open from the bottom end. Is that gonna be a problem?</p>
<p>It may cause an increase in corona discharge depending on how sharp the edges are, but for the most part it should still work. If you add electrical tape or slit vinyl tubing around the edge it should help negate any sharp edges.</p>
<p>Hey I almost made the whole thing but I have a doubt about the dome. I <br> got something that looks just like a smooth round earthen pot, but it <br>is made of steel. I think it will work nice because it is about 12'' in <br>diameter but the thing is that its 6 inch mouth is way too bigger than <br>the 3'' PVC, so if I did fix it on the VDG it will be for all purposes open from the bottom end. Is that gonna be a problem?</p>
<p>Hey i am currently trying to make this VDG and I'm stuk on what material belt to use. I looked up a triboelectric series and found that polyethylene is very negative. So if I cut up a polyethylene bag and use it as a belt will it work?</p>
<p>any material that is between your two roller materials on the triboelectric series will work. If you use the same roller materials as me then polyethylene should work, but otherwise latex or natural rubber work pretty well.</p>
list some belt materials i am unable to find latex and tell me aluminium brush in in bottom or in top,and do both rollers role when i start generator.thanx in advance
You could try any kind of rubber, latex is just more common, or you could maybe try vinyl. There are brushes on both the top and bottom, not necessarily aluminum, but they have to be conductive and have sharp points. Both rollers must be turning when the generator is on in order for it to work.
well, i'm not making this for a specific use or for a project i want some nice long arcs and couldn't this make your hair stand straight?
So go with the teflon on top and aluminum on the bottom, and yes if you are insulated from ground if you hold the sphere your hair should stand up.
Which roller is better to keep on top (+ve one or -ve one)? and can i use woollen coloured thread(crafty one) instead of aluminium? coz wool is more &quot;-ve&quot; right?
It depends on what you're trying to do. If you want longer arcs then put the teflon roller on the top. I wanted positive for future projects, but most people just want longer arcs. I don't know about the thread. I chose aluminum because it is easy to cover the roller with. Thread, not so much. Whether it would work better or not I don't know.
Why does it have to be brushes, why not just a piece of metal? How are brushes different than a block of metal for transferring the electrons?
Because the Brushes have a sharp point, and that's important. Corona discharge will not occur if there is no sharp point (or at least too little to do anything).
How do you make a discharge wand
1. I have 2 inches of bare wire touching my sphere. Is that enough? Do I need more or less? Or it doesn't matter? <br>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?
1. does it matter where I put my top wire. or as long as it is touching somepart of the bowl it will be fine. <br>2. how important is the &quot;no dust&quot; on the parts? <br>3. If my project works will I get a big or small shock?
1. As long as it is touching inside the sphere it's fine. <br>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. <br>3. You will get a decent shock but it will do absolutely nothing other than cause very mild pain.
1. I noticed on my practice runs that the cooper tape on my lower wheel rubs of on the excerisice band. Is this problematic? <br>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? <br>3. I heard the the bigger the sphere the longer the pipe has to be. Is that true?
1. This could be problematic. If the becomes conductive it will not work. If metal is rubbing off onto your belt you may consider a different type of metal tape (e.g. aluminium). <br>2. As long as there is bare copper in contact with the inside of your sphere it will be fine <br>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.
My output sphere is 2 salad bowls taped together it stands at about 11 1/2&quot; tall and 9&quot; width in the middle. Also it is an oval shape. Will this still work? And what can I do about the numbers on the bowl?
Yes, It will work.
Thanks for writing such a well documented and well thought out project. I honestly didn't realise that the rollers needed to be made of different materials, thinking that the difference needed to be between the rollers and the belt, so not only have you LEARNED something by making this project, but by sharing it, you have TAUGHT something too. <br> <br>Well done you. <br>
I recognize your AP human geo book
Yep. I had to do something to prevent myself from having to focus fully on that.
Very interesting, I want to do one of these some day. But, must the belt be made of latex? Why not a plastic belt?
You could use many different belt materials, plastic probably would work. I chose latex because that's what's used in a lot of the commercial VDG's.
OK, thanks for the answer. <br> <br>Another question: &iquest;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.
Higgs Boson I am confused about somethings: <br>1. how big does the hole in the sphere have to be? <br>2. How did you make your discharge wand? <br>3. How did you get the coat hanger to bend the right way? <br>4. I was thinking about making a support for the sphere on the pipe. Any suggestions? <br>5. I was also thinking about putting nylon treaded nuts on the outside of my top roller. Will this effect the ability to discharge?
Higgs Boson I have a few more questions: <br>1. how much of the top roller has to be in the sphere <br>2. for the bottom bruch heres what I am thinking about doing: <br>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 &quot;L&quot; shape at the bottom of the roller where the tips of the of the brush are a bit below the bottom. Will this work? <br>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?
1. To be effective, all of it should be <br>2. that would work fine <br>3. No and no.
I always enjoy seeing what someone did to make one of these. I have often thought I would like to make one, but it is not a practical idea for me. It would be nice if someone could find a way to make an effective and dependable belt from common materials.
It really would. I actually tried and failed with several materials (including a bike inner tube), before just buying a premade one from Edmund Scientifics.
Excuse me Higgs Boson I have a question. I am using wire brushes instead of the copper plate and stickpins. <br>1. do the brushes have to be pointing up towards the roller <br>2. also when I am doing my grounding would a srcew work?
The points of the brush just need to be pointing to the brush. I am not sure I understand what you are trying to do with the screw. Are you using it in the mains ground, or are you trying to make a grounding rod of sorts?
Sorry for that I was going to use a wire brush as the bottom comb. <br>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). <br>2. And also how did you get your sphere from sideing down the pipe I am stumped.
1. That would work fine. <br>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.
Very interesting, I want to do one of these some day. But, must the belt be made of latex? Why not a plastic belt?
do the rollers andbrushes have to fit inside of the sphere? will it still work if it doesn't?
The top roller and rush should fit inside the sphere. It will still work if it doesn't, but there will be more significant losses.

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Bio: Science is my passion. I find myself constantly working on countless experiments, from low energy particle accelerators to good old simple electronics. I also like ... More »
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