Ever wanted to get 40,000 volts to fly through the air? We’ll show you how to build a Van de Graaff generator that will do just that!
A Van de Graaff generator is a device recognisable to most of us - physically, if not by name - often from high school science. Here, we take that desktop-sized concept and build a super-sized one. Why? A better question would be, WHY NOT!
The Van de Graaff generator has its origins in the early days of nuclear research, having been developed by Robert Van de Graaff as a particle accelerator. They are even still used today as high voltage generators, in some specific research fields. Beyond research and high school science education, Van de Graaff generators can actually be a lot of fun! The distinctive metal sphere in the top is the fun zone, where you can cause foil pie tins to levitate and fly away from the top, watch piles of confetti scatter into the air, or see balloons lift off and stick to whatever they touch. You can even make your hair stand on end, zap someone near you (although you will equally share the pain!), and have bright blue electric arcs jump to the grounding rod. It can even form the basis of a lot of photographic fun.
THE BROAD OVERVIEW
The Van de Graaff generator is, in effect, an electron transfer pump, based in the science of electrostatics. To explain this, we have to talk about sub-atomic particles. All matter is made up of protons, neutrons, and electrons. Protons and neutrons clump together in the nucleus, and the electrons orbit them. In some materials, the electrons are attracted less strongly than others, and can be encouraged to move. This is different to materials that conduct an electric current, known as conductors, in which the electrons jump from one atom to the next, to be replaced by another. In electrostatic situations, electrons are stripped from one material and transferred to another. [1]
Underpinning this is the triboelectric effect. Every material has a position on the triboelectric scale, although finding a complete list is near impossible. Many versions can be found that have differing materials on them; however, all revolve around the same concept. When these materials come into contact with each other in a situation involving friction, the more positive one on the scale gives its electrons - or some of them, anyway - to the less positive one. This is because electrons have a negative charge. In real terms, the position of a material as positive or negative on the scale actually relates to the state it will be in after the transfer. So, after losing negatively charged electrons, a material is positively charged. While the reality is more complicated, this explanation satisfies an understanding of the Van de Graaff.
HOW IT WORKS
The basic construction of a Van de Graaff generator involves two rollers, one of a material from the negative end of the triboelectric scale, and one from the positive end, with a belt between them of a material from somewhere on the scale, in between the roller materials. This assembly is mounted in a frame of some sort of insulating material. There are “brushes” of pointed metal that are close to, but not touching the rollers at each end. The brush of the physically lower end is connected to ground, while the brush of the upper end is connected to the metal sphere. One of the rollers is driven by an electric motor, and as it rotates, something happens that isn’t far from black magic. The roller made from the negative material, which likes to “pull” electrons to itself, attracts electrons from the brush and whatever the brush is connected to. However, the belt is in the way, which stores the electrons. The belt moves, and at the other end, it rolls around the roller made from the positive material. This material repels electrons, so they are pushed off the belt and to the nearby brush. They will cross a small air gap in both cases.
The process repeats, with the charge being stored on the sphere attached to the upper brush. It is important to note that Van de Graaff generators can work both ways – by arranging the rollers, the sphere can be negatively or positively charged. If it is positive, the electrons are drawn from it, leaving it depleted of negative electrons and so positively charged. If it is negative, then electrons have built up around the surface of the sphere until it can hold no more. In either case, a charge will build up so strong that the air around it will become “ionised”, or charged, and begin to conduct.
This is called “saturation” and no further charge can be built up. This is the point where sparks will be at their biggest and brightest. Most Van de Graff generators - ours included - have a smaller metal sphere attached to the same ground as the lower brush. This allows the charge to flow back to where it came from, neutralising the charge. This provides both a way or getting the charge to arc reliably, and a way to discharge the sphere when needed.
THE BUILD
Before we begin, I have massive thank you to send to my father, Lester, who is a fitter and machinist by trade. Like all builds, this one had several iterations before the current design, and while searching for off-the-shelf options, my dad manufactured - at short notice and under high pressure - several rollers, shafts, and housings so that I could, literally, get the belt rolling on the initial prototype. Having said this, the project as it is presented, is designed to use no specialist parts, so as to be well within reach of most makers. The DIYODE Magazine team are confident that this would be suitable for an eager school team to build and, with appropriate guidance, within reach of upper primary school students.
| Materials Required: |
|---|
| 2 x 1500mm x 100mm x 50mm PVC Rectangular Downpipe (For framing) |
| 4 x Mounting Flanges for Downpipe |
| 2 x 125mm “Cotton Reel” Boat Trailer Rollers |
| 2 x Shafts for the Rollers |
| 2 x Shafts for the Rollers |
| 1 x Glue-lined 20mm Heatshrink |
| 1 x Leather Sheet (to cover one roller) |
| 1 x Roll Silicon Rescue Tape (Often called “self amalgamating tape”) |
| 1 x White Plastic Chopping Board |
| 1 x Metal Sheet Bracket |
| 2 x Stainless Steel Mixing Bowls |
| 2 x Spherical Curtain Finials |
| 1 x 1.5m x 25mm PVC Electrical Conduit |
| 30 x 20mm 6-gauge Chipboard Screws |
| 8 x 35mm 6-gauge Chipboard Screws |
| 3 x 20mm 4-gauge Self-drilling Metal Screws, Button Headed |
| 1 x 300mm x 90mm x 19mm Pine |
| 2 x 100mm x 90mm x 19mm Pine |
| 1 x Plywood or MDF, at least 300mm x 600mm x 19mm |
| 1 x L-shaped Bracket (Suitable to drill and mount your chosen motor) |
| 1 x Stainless Steel Mesh Frying Pan Splatter Guard |
| 1 x 400mm Length of 40mm PVC Drain Pipe |
| 8 x White 300mm Cable Ties |
| 4 x 15mm M3 Screws |
| 4 x M3 Nuts |
| 8 x M3 Flat Washers |
| 6 x M4 10mm Bolts |
| 6 x M4 Flat Washers |
| 6 x M4 Nuts |
| 2 x 80mm x 12mm x 3mm lengths of Aluminium Bar |
| 2 x 160mm x 12mm x 3mm lengths of Aluminium Bar |
| 4 x 20mm Super Magnets |
| 1 x Polyester Cloth (Big enough to cut, hem, and stitch a 120mm x 850mm belt) |
| 1 x 100mm x 600mm Perforated Steel Bracket |
| Electronic Parts Required: | JAYCAR | ALTRONICS |
|---|---|---|
| 1 x Electronic Speed Controller | MP3209 | K6008 |
| 1 x Electric Motor (Ideally with a 6.35mm shaft) | YM2776 | - |
| 1 x Motor Coupling, (Ideally with 17mm outside dia.) | YG2602 | - |
| 1 x 6m Black Medium Duty Hook-up Wire | WH3041 | W2261 |
| 1 x 1m Red Medium Duty Hook-up Wire | WH3040 | W2260 |
| 6 x Red Eyelet Crimp Lugs | PT4514 | H2031A |
| Note: The printed issue incorrectly lists a requirement for an Arduino, this was an error and is not required. | ||
THE HARDWARE CONSTRUCTION
The parts list is to build the generator in the same configuration as the prototype; however, there are other options. To start, search the internet for a list of materials in the “triboelectric series”. These lists vary, so search them until you come up with some materials that you can source. I found leather at a fabric and craft supply store, polyester cloth from the same outlet, and silicon tape is readily available. However, the best belt material is surgical rubber, which can be hard to find in retail outlets. It can be found online, or your local brand-name rubber supply store may be able to order it for you. The rubber you use should be natural, but much of what’s on the market is synthetic. Be sure to avoid black rubber as it contains carbon, which will conduct at high voltages.
We built a simple sturdy base to support the entire project. It’s just a thick piece of MDF with pine glued and screwed to the outer edges, to increase the strength of the platform. Your base can be adjusted to suit your preferences. Once you have made your base you can move on.
The greater the separation between upper and lower rollers, and between ground and sphere, the more effective the Van de Graaff generator. However, there comes a point where any gains will be purely academic. Our PVC downpipe was cut to 1350mm, which was half the available length. This material can be cut with a hand saw, taking care to keep the ends square. Next, prime and glue the mounting flanges into the ends of the pipe. Then, measure and mark a line across the 100mm surface, 120mm from the top and bottom of each pipe. This will be the centre point of each roller. Now measure and mark a square to be cut out around this centre point to provide clearance for the roller. Using a sharp knife, cut the square out of the downpipe by scoring along the lines several times, Then drill a starting hole in the centre. Use pliers to peel and pry the plastic, which should break along the score lines.
Rollers and shafts need a bearing of some sort. We used the soft, low-friction plastic of a chopping board from a department store for this. Measure, mark, and cut a piece to go inside the downpipe, then mark and pilot drill the screw holes. Next, slide the bearing plate into the downpipe from the end, and attach with 20mm 6g chipboard screws. Start all four screws until they grip, then drive them home.
What you should now have is two pipes laying in front of you on their wider sides, with four plates of soft plastic mounted in them [2].
Next, lay them level and side by side, and remark the 120mm line across them. Now, on one of the pipes, find the horizontal centre of this line - top and bottom. Drill a 3mm pilot hole dead centre. Turn over the pipe that will have the drive shaft through it, and mark the same 120mm lines, top and bottom. At the centre, drill a 30mm or so clearance hole. At the top, this will allow drilling of the second pilot hole while at the bottom it will allow the drive shaft to pass though. Next stand the two pipes in a flat surface. Have someone hold them securely together while you drill through the pilot hole into the bearing plastic of the second side. This will ensure a level shaft [3].
Now you are ready to drill a clearance hole for the roller shafts. The top roller free rolls, while the bottom one is driven. For this, we used a 150mm roller spindle for the top, and a 235mm spindle for the bottom, which we purchased from the same retailer as the rollers. Both are glued with liquid nails - the top one centred, and the bottom one with just enough on one side to engage the bearing, so as to leave a long enough shaft to pass through the downpipe, to engage the motor. Cut the conduit joiners in half and place one half on each side of each roller [4].
At this point, you can coat the rollers. This is critical to the operation of the generator, so do it carefully. The lower roller on the prototype is covered in silicon tape, which should be applied using the package instructions. The ultimate roller shape for a belt is with a slightly convex crown, so we layered tape toward the centre. This helps to keep the belt centred. The top roller is covered with leather, rough side out. Mask off the shaft, then spray both the leather and roller with contact glue. Allow the glue to become tacky, then stick the leather down. We used one rectangle for the centre of the shaft, and smaller, shaped pieces to cope with the curve at the ramped end of the roller.
It will now be prudent to dry-fit the components on the base board, using the photos and diagrams as a guide. Mark a centre line on the long axis of the base board, and mount the frame along this line. Screw down the non-motor side using 20mm chipboard screws, then adjust the position of the motor side so that the roller shafts freely rotate. Screw this side down as well. You don’t need to get too carried away with this, as one side will be removed later, to add the belt.
To assemble the motor support frame, drill a hole to mount the motor in the L-shaped bracket. Ours was a 12V DC motor, which had a 17mm flange around the shaft, and M4 mounting holes. These were marked and drilled, along with screw holes, in the base of the bracket to mount it. Measure the distance between the centre of the motor shaft and the bottom of the bracket, and subtract this from the distance between the centre of the lower roller shaft and the base board. This number is the height of your support frame. Subtract again, this time taking away the thickness of the 300mm x 90mm pine, which should be around 19mm. Mark the two 100mm x 90mm pieces of pine to this number, then drill and screw to the 300mm piece using 35mm chipboard screws - see photos.
Next, add the shaft coupling to the motor shaft. Our prototype had a 5mm shaft, which had to be bulked up to centre the coupling. This was done with a strip of 0.5mm plastic, leaving a gap for the grub screw on the coupling to be firmly wound down against the shaft. Align the coupling with the roller shaft, leaving 10mm between them, and pencil around the support frame. Remove it, drill holes along the centre line of each frame leg, and then screw into the wood from underneath. Now the motor support frame should be secure.
Here comes the tricky part. Manufacturing the belt is challenging for someone with no sewing skills so seek help if you’re unsure - even a clothing tailor in a shopping centre could probably do this for you in a few minutes [5].
Measure the flat section of the rollers between the ramps, and double this number. Then measure the distance between the rollers. Our total length was 1040mm from the outside of each roller. Fabric does not come wide enough to go this entire distance, so two halves of the belt will be made and sewn together. However, the fabric stretches a lot, and our final belt was 800mm long, giving a total length when opened out, of 1600mm. Our fabric was 1470mm wide; however, if you purchase 2m, you can make a belt with just one join.
Carefully mark a piece of fabric long enough to complete the loop around the rollers, and wide enough to be doubled over and hemmed. For our prototype, this was 120mm. Start with a long length for the belt, and cut out bits until you have the right tension. Ours went from 2080mm to 1600mm. Start by hemming each side of your strip, then fold the edges in to the middle. Stitch them down the length of the belt according to the diagram. Now stitch the ends together to form a loop.
Unscrew the non-driven side of the frame, remove it, and loop the belt over the rollers. Reassemble the frame, probably with help as the tensioned rollers will need to be guided into their bearing plates. Spin the lower roller’s drive shaft by hand, to make sure if rolls freely. If it does, all is well. If it doesn’t, check nothing is impeding the free movement of the rollers. If they don’t spin freely you risk burning out your motor, or shredding the rollers.
Glue the two mixing bowls together using a conductive glue product. We used a product called ‘wire glue’ but other varieties exist - check your local electronics or hardware stores. This glue needs to cure overnight. While it is hardening, you can make the brushes. They are made from mesh using a frying pan spatter guard, and 12 x 3mm aluminium strips. Cut two 80mm lengths and two 160mm lengths. Clamp one 80mm piece to one 160mm piece, and drill 3.5mm clearance holes as per the diagram.
Mark a line at 110mm and bend at 90° so as to form an L-shape. Then, cut an 80mm x 160mm long strip of mesh, and remove half of the horizontal wires by gently unpicking them; you’ll be left with a brush that looks a lot like a fine hair comb. Fold this in half length-ways, clamp between the two aluminium strips, and drill clearance holes. Assemble with two 15mm M3 bolts, four washers and two nuts [6]. Make two of these.
Now the bracket at the top of the mixing bowls can be added. This was made from a 100mm x 600mm length of perforated general purpose mending bracket, from a major hardware store (in the same section where you find corner and shelf brackets). Measure the distance to the outside of the flanged mounting brackets at the top of the downpipe frame, taking care to make sure the top roller spins freely. We used six M4 mounting screws to mount ours through the existing holes in the bracket and flanges. This secures the top of the frame and provides a magnetic mounting point for the bowls.
High quality stainless steel is not terribly magnetic. Even 20mm supermagnets did not stick well to our bowls, so we stuck ours with strong double-sided tape, covered over with gaffer tape. This formed a strong but removable mounting for the bowl to sit on top of the frame.
Mount the brushes into the PVC downpipe, using a 20mm self-tapping screw in each straight. You may need to trim the brushes, but this allows an amount of adjustment so that the brushes can be made to sit just above the belt. Take a length of black hook-up wire, making sure it’s long enough to go from the top brush to the bottom of the sphere, and crimp an eyelet to each end; one is attached under one of the nuts and washers already on the brush assembly. The other gets attached to the bowls with a self-drilling metal screw. Cover this screw with gaffer or insulating tape. The top of your generator should now be nearly complete.
At the base of the unit, the other brush is secured the same way. It must be under the roller, and using an eyelet, a length of hook-up wire is attached and reaches all the way to the far end of the base board.
DRIVETRAIN / ELECTRONICS CONSTRUCTION
The last step in generator construction is to mount the motor and connect it to the belt drive shaft. Slide a 50mm piece of 20mm diameter glue-lined heatshrink over the drive shaft. Then screw down the motor bracket in the position described in the construction paragraph above, and slide the heatshrink to cover the shaft coupling and the shaft. Shrink it down, rotating to keep the fit even. When cold, this creates a strong, yet flexible bond. You can now screw down the motor bracket. Solder connecting wires of red and black hook-up wire from the motor to the speed controller, and from the controller to the power supply. We used a 7.2Ah sealed lead acid battery; however, a strong enough plug-in supply would work. The exact details here will depend on your motor choice.
All that is left now, is the grounding rod and grounding connection. At a major hardware supply store, we found a pair of spherical steel curtain finials around 50mm in diameter. Remove the screw from one, detach the tubular frame, and wrap the stripped end of a 500mm length of black hook-up wire around the screw; then firmly screw it in. The other end of this wire gets an eyelet. Repeat this procedure on the other finial; however, this time, use the remaining length of black hook-up wire, and retain the tubular connector and its grub screw. Pass the wire down the inside the 20mm conduit, and attach an eyelet to the other end. Now use the grub screw to mount the finial to the end of the conduit, bulking up the diameter with tape if required. This forms the grounding rod used to draw an arc or to discharge the sphere.
The eyelets on the wires from the discharge rod, the grounding sphere, and the lower brush are now anchored together with a 20mm chipboard screw on the base board. The grounding sphere sits on the ground when the generator is in use, allowing electron transfer to occur.
FINISHING TOUCHES
The final step is to add spaces that keep the belt centred on the rollers. These are 95mm lengths of 40mm PVC drain pipe, secured with cable ties near the rollers. These are critical for the belt to be held centre. In the “where to next” section, there are ideas for more complicated but effective ways of belt centring.
That completes your Van de Graaff generator! Check over the photos and diagrams provided, and get testing! You really don't need to follow our construction method too closely if you don't want to. The important aspects are using the right materials, and using conductive or non-conductive materials - as appropriate.
WHERE TO NEXT?
Those who possess or have access to machining equipment and source material, will benefit from custom-made parts. Rollers with a convex crown could be custom made, as well as shafts and shaft couplings. Motor connection could also be geared or belt-driven if you are familiar with such processes. This would be more reliable and effective, but is out of reach of many makers.
Further, a surgical rubber belt or tubing would possibly add effectiveness to the unit, although we were unable to source and test this in time (genuine rubber is quite expensive too).
Adjusting the position of the brushes may yield different results, and it is worth noting that commercially-produced Van de Graaff generators have the sphere mounted over the top roller and brush assembly. This is more effective, but harder to achieve unless you possess the metal working skills required to cut the high-carbon steel and clean the edges.
Construction could also take the form of acrylic frame sides of a single thickness, rather than the rectangular tube of the PVC downpipe; however, for structural integrity, front and back panels would need to be added.
The ultimate way of achieving belt centring is with shafts mounted to ball bearings in adjustable housings. These are hard to source and use if you are not familiar with them, but anyone working around machinery will know them. They are a housing that allows adjustment of the bearing in one or two planes, creating a way to align the shafts and stop the belt wandering. If you can source and use these, you probably know enough about them, as they are regularly used on conveyor and flat belt systems.
Some final modifications could be a reversing switch to experiment with the direction of the belt and its effect on charge, and changing roller materials. You could even change the orientation, having the negative material at the top and the positive at the bottom.
At the end of the day, this is a fun piece of equipment made from VERY easily sourced materials, that viably demonstrates a useful scientific concept in a way that everyone can have fun with. Modify it, play with it, change materials and see what differences it can make!
A word of warning however: a generator this size creates an electric shock much more powerful than the small variety. Use it with caution. Although it is unlikely to create health effects, it can hurt and cause surface skin burns.