loading
   



        The Van De Graaff Generator invented in 1929 by Robert J Van De Graaff uses a couple of rollers, combs, and a rubber (or nylon) belt to create a charge of a few thousand volts.  This charge is drawn off into the center of a hollow metal sphere, this last process takes advantage of the Faraday Ice Pail effect to multiply this charge to tens or hundreds times the input voltage.
       The charge production occurs in three main areas: the rollers/belt, the combs, and the output terminal.

       There are two main types of Air Insulated VDG's, externally excited and self exciting.  This instructable will focus on the latter as any self excited VDG can be easily converted to an externally excited unit by attaching a high voltage DC source to the lower comb and removing the comb from ground.

The rollers in this unit must be selected so that they are as far apart on the triboelectric series as is possible.  Below is a simple chart for reference:

Triboelectric series

  • Human Hands (if very dry)          +++ Positive +++
  • Leather
  • Rabbit Fur
  • Glass
  • Human Hair
  • Nylon
  • Wool
  • Fur
  • Lead
  • Silk
  • Aluminum
  • Paper
  • Cotton
  • Steel                                                       (neutral)
  • Wood
  • Amber
  • Hard Rubber
  • Nickel, Copper
  • Brass, Silver
  • Gold, Platinum
  • Polyester
  • Styrene (Styrofoam)
  • Saran Wrap
  • Polyurethane
  • Polyethylene (scotch tape)
  • Polypropylene Vinyl (PVC)
  • Silicon
  • Teflon                                                --- Negative ---    



  For this unit I used a PVC(vinyl) roller for the top and a Nylon Roller for the bottom, this will give a unit that has a negative output voltage.  To create a unit with a Positive output voltage simply reverse the roller arrangement.

  Instead of the standard spherical output terminal I recycled a helium tank as the output terminal.

  This is not going to be a specific article on how to build this particular VDG (Van De Graaff [saves typing]) but rather what you must do to build a VDG.  I will however try to explain the processes involved for each of the components necessary so that you will have a concept of what it is supposed to do which will aid you in your own construction and troubleshooting. 

Whether you decide to build a large 700KV model or a small table top unit the components are exactly the same only the size is different.  Also when it comes to VDGs,  size does matter, as the output voltage is determined by the size and shape of the output terminal, the size of the rollers, the speed which the charge is delivered to the upper roller, and the distance between the rollers.

  So while this unit which is just about 4 feet tall and delivers approximately 500,000 Volts I have a table top version that is 22 inches and only delivers about 80,000-90,000 volts.  So if you don't want to commit to a large project then you can build a small unit and then scale it up once you are familiar with construction techniques.

The last photos are of my first VDG project and you will see the components are the same as in the large one.  This was created from an online article here:  

scitoys.com/scitoys/scitoys/electro/electro6.html




Step 1: Parts List

* Furniture rollers (see step 3)
* ~2 inch OD PVC Pipe (1 1/2 inch ID)
* 4 inch ID PVC pipe - 2-3 feet long
* 4 inch mounting flange
* 4 inch connectors
* Steel rod for axle
* 'Skateboard' Bearings, or other sealed bearing
* Electronics perfboard or circuit boards
* Stick Pins
* Lamp Dimmer Switch
* 120V AC Toggle switch (may be optional, see step 2)
* Fuse holder
* AC Electric sewing machine engine or other 1/8 to 1/2 HP AC engine
* Output Terminal (Stainless Steel Gazing Globe, Helium Tank or other metallized globes
* Nuts, Bolts, Screws, etc.


Step 2: Motor and Mounting

On both of my larger units I have used a salvaged sewing machine engine to drive the unit.  This arrangement creates a direct drive and simplifies the build process.  If you do not have one or cannot get one then you can select an AC motor and use a pulley arrangement to drive the lower roller.

I didn't get too fancy with this step because the base that I used did not have a lot of room to mount the motor so it is attached to the underside of the base with shims to level it.  The drawback to this is that there is limited adjustment and the motor vibration travels to the whole device.  Perhaps when I rebuild the base I will mount this on a spring loaded platform.

Motor speed is controlled with a standard lamp dimmer switch.  You should hook it up first to see if it starts at the highest voltage or the lowest.  If it starts at the highest you will need to add an On/Off switch and set the dimmer to its lowest setting when starting to avoid straining the belt and bearings.


Step 3: Roller Construction

 

  The lower roller is from a set of furniture rollers and has an OD of 1 5/8" this has a pre-drilled center hole and I had to enlarge the hole slightly and use some alcohol to get it to slip onto the motor shaft.  This permanently mounted the roller to the shaft once the alcohol evaporated. Also this roller had a slight crown to it, this is desirable as it helps the belt track straight when operating.

The upper roller is a 2 3/4" long section of 2" diameter white PVC pipe.  Two skateboard wheels were used as the center hubs for the upper roller.  I bolted them together and mounted them in a drill press and sanded them until they could be securely pressed into the PVC pipe.  The roller was placed in a chuck  holder of a lathe and the ends were sanded to give the center a crown.  Bearings were inserted into the wheels in the roller and an axle is passed through the center hole of  the roller and with locking collars to keep the roller centered and the axle was mounted into bearings at each end. See the picture for more detail.

Step 4: The Base

The base was constructed by attaching 2 - 19.75" 2x4's to a 21.5" by 12" piece of particle board.  One end is closed by a 12" 2x4.  The other end is a piece of particle board to mount the switch on.
Most people recommend acrylic or other plastic building materials to prevent moisture absorbance.  It you choose to use wood or particle board a coat or two of urethane should coat it well enough to prevent moisture issues.

A hole was cut into the deck for the belt to pass through and a PVC closet mounting flange was mounted to the deck.  The column is 4" diameter PVC pipe from a hardware/home center and was sold in precut 2' lengths.  You can cut your own but you need to be able to make the end square so that the column does not lean to one side or the other as this will throw off the tracking and make the belt jog to the side at high speed.

There is not much wiring necessary.  Put the dimmer switch and the fuse holder in series with the hot side of the AC power line.

Step 5: The Support Column

The Support column serves two main functions:
1. Separate the upper and lower rollers.
2. To support the output terminal.

The support column should be selected to allow adequate clearance for the belt .  The height of the column depends in part on the size of the output terminal; the general rule is that the distance between rollers should be at least 1.5 times the diameter of the output terminal.  So for a 12 inch diameter output sphere you should have at least 18 inches between the rollers.  On my unit I used a pre-cut 2 foot length of PVC to ensure I was working with square ends, as I did not have a reliable way of making square cuts on the PVC.  When you add in the distances for the upper connector and roller assembly and the distance as it passes through the base to the motor it adds almost another foot.  So in this unit the distance is probably twice the ideal length between rollers.  A shorter column would have been better all around to reduce charge losses, but I had to work with what I have.  If you have access to a power miter saw or your local home supply store has a power PVC tube cutter and can cut square ends then you may be able to have them cut to your specific needs.

Secondly the entry hole in the output terminal will fit over the 4 inch PVC pipe and comes to rest atop the coupler that joins the support column to the roller assembly.  The inner sleeve has a corona dampening collar to reduce corona discharges and the sleeve itself helps stabilize the output terminal on the support column.

Step 6: The Belt Construction and Adjustment

This part is probably the hardest step but is a crucial step for a successful build.
I have tried many different materials for the belt and some just don't work and others work but are tedious to fabricate.

The two most readily  available materials to use are exercise rubber banding or common roller shade material.  If you ask your local hardware store they may be willing to give or sell you the cut off pieces as most stores usually discard these anyway.

The rubber belt will give the best charging current of the two but suffers from stretching or lifting at higher speeds this causes problems maintaining proper tracking.  The rubber belt material is also very difficult to cut in a straight line as it tend to stretch even with a very sharp blade so you must take your time and be extra careful.  I find it easier to lay the material flat and use a straight edge to make a line then use a ruler and razor to cut along the line.  It is always best to have one square (factory) edge to ensure your belt is straight

The roller shade material doesn't provide as much charging current but once 'broken in' can be operated at higher speeds without lifting or having tracking problems.  The roller shade material is easier to cut as it does not stretch when cutting, it can be cut with a rotary craft knife or scissors.

In any case the belt should be narrower than the roller.  For example if your rollers are 2 inches wide than you should have a belt no wider than 1 3/4 inches.   Remember when using a rubber belt the width decrease by about 1/4 to 1/3 when under tension so cut to at or slightly narrower than the roller.  Also you must splice the end together at an angle because if they are cut square across they they will lift over the roller and eventually damage the bearings.

In previous builds I had spliced the ends at a 45 degree angle.  But I recently read how others are using a V and reversed V to splice them this makes the center of the belt pass over the roller at the splice and spread outward evenly across the roller.

I have found two products to be the best for securing the belts to themselves.  For Rubber belts the best glue I have found is suprisingly super-glue.  For the Vinyl roller shades a product called Vinyl Welder.  I recommend allowing the adhesive 18-24 hours to cure before using the belt.

If you opt to install the motor on an adjustable platform you can make adjustments there or you can make a spring mounted  upper roller assembly as I have done to adjust tracking.  Or if you want to mount the bearings inside the hub you can simply cut slots along the sides of the PVC column (as in the last picture) and use a threaded axle and secure the axle with lock-nuts.

Step 7: Combs

The combs spray the charge onto the belt at the base and pull the charge off the belt at the top.  They can be as simple as stripping some stranded wire and fanning out the individual strands as shown on the table top VDG. 
You can fabricate them with stick pins and perfboard or as in the third picture by salvaging pieces from other equipment. This was the metal tear off strip from an adding machine.
When designing the mount you should provide a means to change the distance from the comb to the roller.  It is also desirable to be able to move the comb around the the roller.  I find the comb at or near the separation point to be most effective.  Others have said the best point is directly above the top roller and directly below the bottom roller.  Again experimentation will determine the best placement for your build.

Step 8: The Output Terminal

The output Terminal is usually a large hollow sphere, however other shapes can be used as shown by the recycled helium tank I used on this project.
The main thing is that it should have a smooth finish to reduce corona leakage, no sharp turns or angles which would tend to draw off the charge.

The problem with metal spheres is that they are EXPENSIVE!!. Up to about 12" spheres can be had for less than $60.00, but any larger and the price shoots right up.  Do a search for Stainless steel Gazing Globes and you will find that for a 20" diameter globe you can expect to pay $165.00 to $240.00 online; while a 24" sphere will run into the $1000.00 range.

For smaller units the 8" metallized plastic ornament balls can be used as shown in the third picture.
If you go looking close to or after the holidays you can buy these for 50%-75% of the original price.

Another option people have tried is joining two stainless steel bowls together and taping over the rim to reduce corona discharge.  This can be an extremely  inexpensive way to go as the bowls do not need to be high quality and if you make a mistake cutting the entry hole on a $2.00-$3.00 bowl its not as devastating as it is on a $30.00-$50.00 Ball
Once you have your output terminal the next step is to create the entry hole because the charge has to be applied to the inside of the sphere to obtain the higher voltages.  I recommend an angle grinder or a cut off wheel for cutting stainless steel to make the entry hole. I would advise against a jigsaw as the vibration may crack the sphere.

The ideal shape would be to have the sides of the entry hole curve back up and into the sphere, but Stainless steel is not malleable and if bent to much will fold and buckle.  Therefore the use of a corona ring is highly recommended.  This is just a soft copper, ring that is soldered or press fit around the entry hole as I have done.  The ring significantly reduces the corona leakage at the entry hole and allow the output terminal to charge to a higher potential.

Step 9: Pictures of the Van De Graaff Generator Operating

These photos were taken under normal lighting conditions with a 5.1 Megapixel digital camera.  I had the generator running and just started clicking away, there were some photos that did not show any sparks but those that did I thought were kind of cool and wanted to share them with all of you.

Toddjwood


is the comb neded?, can't vork witha  plate?
Hi,<br /> Thanks for looking and the comment!<br /> <br /> The purpose of the 'pointy' ends is to increase the amount of corona discharge.&nbsp; It is the ionized air that actually charges/discharges the belt.&nbsp; The sharp ends help raise the output voltage to the breakdown voltage of air allowing the charge to travel through the air and charge the belt or pull the charge from the belt.&nbsp; Having multiple ends increases the number of regions that are charged.&nbsp; The surface of a plate would not effectively transfer the charge, it would have to be much closer (thousands of an inch) and the voltage would not be as high.&nbsp; Think of it as pumping water through a large pipe into a very small pipe, the pressure increases as the same volume of water tries to travel through the smaller diameter pipe.&nbsp; As voltage is electrical 'pressure' you can use the same analogy.&nbsp;&nbsp; <br /> Hope this explanation helps.&nbsp; <br /> toddjwood<br /> <br />
<p>where does the combs wire go</p>
thanks&nbsp;
<p>is it mandatory to use only spherical shape dome</p>
<p>was very good . I wonder what material you used for the belt and what can I replace that I can find easily ?</p>
<p>I have used rubber and vinyl exercise belt material and I have also used roller shade material. The exercise belts can be ordered online or at fitness stores and the roller shade material can be gotten from any hardware store (if you ask real nice they may be willing to give you the trimmed end that get cut off for little or nothing!). The rubber stretches some so it doesn't track as well at higher speeds. The roller shade material doesn't carry as much of a charge but if clean and dry(low humidity) it works well and tracks better at higher speeds. Thanks for looking at the project.</p>
<p>Thank you</p>
does anyone know how to make a discharge wand. I am confused.
I have used a 2-3 inch spherical knob mounted on the end of a pvc tube, for the ground wire I used an old 3 conductor extension cord with all three conductors joined together and mounted to the knob on one end and connected to a large battery clamp on the other end. connect to any earth ground, (cold water pipe, Metal rod in the ground, etc) and your good to go.
Just wondering, what would be a rough estimate of the cost? <br>
It's hard to give an estimate as I used recycled parts where ever possible but depending on how much you can salvage $50-$70USD. The most expensive being the Sphere, bearings and belt material.
Ok thanks, I think i will have to replace some of the parts for cheaper stuff and i have a lot that I can salvage...
Just found this site. Many years ago I built one of these but full size to power a home-made &quot;accelerator&quot; tube to produce radiation, which it did until the tube outgassed. Stood about six feet high. I need to post a picture of that setup. Spheres were 16&quot; diameter and I primed the device with the output from an old black-and-white TV.
Great instructable. I especially appreciate the explanation at each step. Many projects focus on the specific 'how to' of a particular build strategy without conveying the 'why' that step is necessary. That may allow one to duplicate the build if they are lucky enough to have exactly the same components (which is unlikely given the recycling nature of most makers) but doesn't prepare one to make substitutions when necessary nor to troubleshoot when the inevitable opportunities arise. At the end, one may (or may not) have a working project but they won't know why (or why not) nor how. I learned more from your instructable than from the dozen or more others I read before it...combined. Thanks for the wonderful lesson. I'm looking forward to trying one of my own. <br><br>May I hazard a guess that you are/were a teacher? Your enthusiasm and style remind me of a couple of my teachers (that's a good thing just in case that wasn't clear ?).
Dear kenwilson,<br><br>Thank you so very much for your kind comments, I really needed it right now!!<br>The very first VDG I constructed was from an online article at this URL:<br><br>http://sci-toys.com/scitoys/scitoys/electro/electro6.html<br><br>It was relatively easy to build (and modify) and after seeing the voltages it developed I was hooked. My next build was full size and much more difficult but I joined the Van De Graaff generator group on Yahoo. Those folks are quite knowledgeable and happy to share what they know as they love to build them as much as I do. (I recommend signing up with them)<br>Good luck with your build, should you run into any snags, post a comment and I will see if I can help.<br><br>As to be a teacher, no, just a geek who loves to build High Voltage stuff.<br>Thanks again,<br>Todd<br>
Hey,<br>I really liked what you made and even im trying to make one. But the problem is that i have just about 10-15 days for my school science fair to go, and i need to construct one for the fair. Can you please suggest me some easy and simple ways to construct this in such a short time?<br>Pleas help me. You can contact me through email- raghu.jjj@gmail.com
There are many websites that offer instructions, start by searching google or youtube for ideas. Start with something small as this will be the easiest to construct. Make it as simple as you can and then you have less to go wrong.
can you touch it safely?? bare handed
Thanks for looking!<br><br>yes the current is very low and it is only slightly more painful than a shock from the carpet.<br>Of course you should never discharge a capacitor or leyden jar charged on a Van De Graff Generator through your body! That could be fatal!!!!
Does the globe on top have to have a hole in the bottom? Should the brushes be touching the belt? <br>
Yes the charge needs to be applied to the inside of the sphere to obtain voltages higher than the input. No the brushes should be as close as possible but not touching.<br>Thanks for looking and feel free to ask any other questions.
I've taken a large hamster ball and covered it in aluminum duct tape. Not that plastic &quot;duck&quot; tape, I mean real duct tape that is actual aluminum. <br> <br>Haven't finished it yet, though I have confirmed that there is enough contact between the pieces for it to have electrical continuity. <br> <br>I didn't cover one of the hatches, I've cut a hole in it and glued it to a PVC coupler to more easily attach it to the support column.
Hi,<br>Before I discovered that the xmas globes will work, I covered one in aluminum duct tape. I used it as a ground terminal on my first and later as an output terminal on a mini that I built. I works but even with smoothing it there will be some corona leakage. I have attached a pic for reference. The small globe in the pic is a plastic ornament. These come in a variety of sizes and can be had for little money at the end of the xmas season. They work well on small ones but the metal paint vaporizes on larger units.
i've been trying to figure out how will my hair stand!!!! my van de graaff won't work even how many times i had tested it..... i think the problem is with the belt,,,,,, can you tell me what material should i use for the belt except for the ones you already gave? can i use a tourniquet ???? and can you give me some pointers???? i really need it...asap
Jeslie,<br><br>Sorry for taking so long to reply, haven't been on the computer in days.<br><br>Rubber tourniquet should work, though it won't be that wide. You don't say how large your Van De Graaff is so I don't know if the width would be an issue. There are many other materials that can be used. Google &quot;Van De Graaff Generator Belt Material&quot; and you should find some good links.<br>The charge is developed first at the separation of the lower belt, so make sure that the comb is at or close to this point. If the comb is on the wrong side little or no charge will develop. The same goes for the top of the belt, the comb should be at the separation side. Some people have reported good results with the comb directly below the bottom roller and directly above the top roller. Finally the comb should be as close to the belt as possible without making contact with the belt.<br><br>The combs can be as simple as some strands of wire fanned out, the main idea is to have pointed or small diameter wire to concentrate the charge. The lower comb assembly must have a very good ground, preferably an earth ground.<br><br>If you are creating a self excited VDG then the roller materials should be as far apart on the Tribo-Electric scale from the top of the page.<br><br>The two biggest 'killers' of VDGs are Dirt and humidity. Both of these serve to dissipate the charge before it can be created. Make sure it is clean!! If the relative humidity is above 30-35% then consider a 'dryer'; this can be as simple as a low wattage light in the base, this will help dry-out the components and lower the humidity inside the unit. Also, make sure to cover the lower part so that it cannot pull dust and dirt from the the floor;ground. I recommend using alcohol to clean the components, including the belt. I have used soapy water and then a hair dryer to dry the belt, If you dry the belt with a cloth it should lintless so that you are not transferring lint to the belt while drying.<br><br>Well that's about all there is to advise on, let me know if this helps or if you are still having problems<br>Todd
&nbsp;I built a van de graaff but it isn't working very nicely, the better spark I can get out of it have 3cm or so. The bottom roller is PVC covered with leather and the top one is PVC tubing, the belt is made of vynil(PVC) and the combs are pretty close to the belt. The output terminal have only 15cm of diameter but I should get a bigger spark from it, don't you think so? Also, the output terminal are pretty round
Hi Joauml,<br /> The maximum voltage the output terminal can charge to is in part determined by the size of the terminal.&nbsp; The larger the terminal that larger the output.&nbsp; check out step 8 for tips on alternate ways to create the output terminal.&nbsp; The terminal in this project is about 33cm by 38cm and can easily produce sparks 15cm to 22cm.&nbsp; the small units pictured in the article have an output terminal 20cm in diameter and only produce sparks 5cm to 7cm.<br /> <br /> Fast Motor speed is not necessary to create a large charge, it is the output terminal.&nbsp; A fast motor will help maintain the charge which is constantly drawn off by discharges a the entry hole and the terminal itself.<br /> <br /> Belt width, belt material, roller material, diameter of the rollers and the distance between the rollers all play a part in 'pumping' up the charge.<br /> Think of charging like blowing up a balloon, there is constant pressure outside the balloon to remove the air inside, if you pump more air into the balloon than it can handle it will leak out where the air is being pumped in or it will break.&nbsp; Obviously the output terminal does not break,it is the air around the output terminal that breaks down and allows the terminal to discharge through the entry hole or to a nearby grounded object.<br /> Good luck with your project and thanks for looking and commenting<br /> Toddjwood<br /> <br />
I forgot to mension: rollers have about 30mm of diameter and the motor isn't that fast
Here's a question I've had for some time:&nbsp; Suppose you started with a papier machet globe and carefully applied aluminum foil to the outside in such a way that there were no wrinkles does this sound like a feasible approach to making a terminal?&nbsp;&nbsp;<br />
You could take this approach, but the paper mache must be completely dry.&nbsp; Even with that it would still be prone to absorbing moisture.&nbsp; I have used plastic globes with strips of aluminum tape and smoothed them out for use as a terminal.&nbsp; Also as in the third picture above plastic ornaments with a metalized coating work well on smaller units.&nbsp; The ones above are 8&quot; in diameter and produce a pretty decent charge.&nbsp; Another approach many use is Stainless steel salad bowls, if you can find the rimless kind that works best but it will work with the rimmed ones as well.&nbsp; These can be found in discount stores for $2-3.&nbsp; They are thin but this makes working them easier.&nbsp; I usually use a hole saw to punch out the entry hole in one and clip the bottom to the top.<br /> Thanks again,<br /> Toddjwood<br />
What about cotton or wool cloth for the belt material?&nbsp; Those two materials are in the middle of the Triboelectric series and they should have good mechanical belt characteristics.&nbsp; The only possible down side I&nbsp;can think of is they are absorbent to moisture.<br />
Hi,<br /> Thanks for taking the time to look at my Instructable!<br /> <br /> Yes they are both absorbent to moisture and both are not particularly good insulators.&nbsp; you need to use a material that will not allow the charge to pass through the belt to the rollers.&nbsp; Most of the charge is developed by the separation of the belt from the roller.&nbsp; Triboelectric actually means electricity by friction, but the charge is developed because the two materials have a tendency to either lose or gain electrons when the dissimilar materials separate.&nbsp; The rollers will become charged with opposite polarities and the combs are used to pull charge off of the belt or spray electrons onto the belt. With a good insulator the charge is held long enough to reach the top of the VDG and can be collected inside the output terminal.&nbsp; This is why there are different materials used for the upper and lower rollers.&nbsp; The belt is essentially neutral and will hold either a negative or positive charge.<br /> Having said all that, people have used both materials for belts and if woven tight enough and kept dry they will work. but they both also produce lint which will dissipate the charge and require more frequent cleaning.<br /> <br /> Yes, I know I talk a lot. sorry.&nbsp; I hope this answers your question.<br /> toddjwood<br />
This things have fascinated me for the last 50 years.&nbsp; I made a weak attempt at building one about 20 years ago, but did not have a suitable belt.&nbsp; It was also a very humid area, and I am sure that made electron collection at the combs difficult.&nbsp; Congratulations and thank you for sharing.<br />
SWEET!!<br />

About This Instructable

50,333views

63favorites

License:

More by toddjwood:Homemade Van De Graaff Generator 
Add instructable to: