My oldest daughter decided she needed a science fair project and I came up with about 30 different things she could make. She decided to build a Van de Graaf generator and I set about doing some research on the net and finding parts. There is a lot of material on the web about building Van de Graaf generators, how they work, and so on. I won't repeat much of that here. A good article is at http://www.howstuffworks.com/vdg.htm. About a week or so into the project my wife tells me that my daughter has changed her mind and wants to do bio-feedback instead. So now not only do I have a load of VDG parts I don't really need but now I also have to get the bits for what she's decided to actually do. Anyway, I decided that finishing the VDG would be fun so I did.
Since building it, I've taken it to my son's school and zapped a few 2nd graders which we all enjoyed. We've lit up fluorescent tubes in the workshop and done a lot of assorted electrostatic experiments. The whole thing cost under $200 of which the biggest item was the motor for which I paid about $80.
Figure 1. The top electrode being made
The first picture shows the top electrode. This is actually the second one of these I made. The first one was made by blowing up a balloon and covering it with paper mache and then covering that with aluminum tape. It was about 12" in diameter and didn't work all that well. You can actually see it in figure 4 below sitting on top of the electrode shown above. This design works much better and is actually a lot easier to make. I used a piece of 5" dia. heating duct bent around into a toroid. I taped a cardboard disk to the top and then covered the entire thing in aluminum tape. You can see a piece of the duct and the roll of tape in the picture. I sized the hole in the center to just fit a 4" to 3" PVC reducer which is part of the top assembly and again you can see that in figure 5 below.
Figure 2. The assembled machine showing the PVC arm used to hold experiments.
Figure 2 shows the final assembled machine. Note the hair dryer on the bench which is used to dry the belt when we first start it to get maximum performance.
The main piece is a 1/4 HP motor mounted on a 3/4 plywood base. The base was stained and varnished to give it that 'science' look. The main support for the top electrode is a piece of 4" PVC pipe standing in a PVC pipe flange. the belt runs up inside the pipe. The terminals shown in front of the motor are both connected to ground and are used to connect other spheres and so on for experiments. They are also handy if you want to keep yourself from building up a charge while the machine is running. Just attach a wire to one terminal and hold the other end. This helps make is safe to turn off the power switch without getting a shock.
Figure 3. A close-up of the base.
The lower part of the support is made from pieces of PVC pipe and end-caps holding a Plexiglas plate. The plate has a 4" hole cut in it to let the belt pass through. I drilled the PVC end caps and used 1/4" bolts to mount the support tubes to the base and plate. The lower pulley on the motor is turned from nylon. It has a slight barrel shape to help keep the belt centered. The nylon is covered in self-amalgamating silicone tape. The belt itself is made from latex rubber sheet which I bought as a 6" wide strip and cut to 2" wide with scissors. You can see the join in the picture which is diagonal to help it run smoothly over the pulleys. The join is made by overlapping the rubber about 1/4" and using super glue (the gel kind) to bond the pieces together. In front of the belt, two brass pillars support an electrical grounding block (as used in circuit breaker boxes) which is used to hold the brushes. The brushes are copper wire bundles which are cut so they will be close to the belt but not touching it. The metal assembly is grounded (you can see the green/yellow wire). The picture shows an arrow on the motor which I intended to indicate the direction of rotation. This is wrong. It actually revolves the other way so that the belt is going up past the brushes.
Figure 4. The completed machine with an older top electrode on top to add some area.
Figure 4 shows the machine with two electrodes on top. I was experimenting with increasing the capacity of the top electrode.
Figure 5. A Close-up of the 4" - 3" PVC reducer which forms the top mount.
The final picture shows the top pulley assembly. The top pulley is a barrel shape again and this time it's made from aluminum. The pulley runs on a brass rod shaft with just a little grease on it. Keep the grease away from the belt. The belt is under very slight tension. You can see the top brushes which are made the same way the bottom set are. I cut away some of the PVC to mount the brush set. This was pretty fiddly to do and I'm sure there are better ways. A wire connects the brush assembly to the top electrode shown here removed and hanging off to the side.