Simple Van de Graaff Generator

By Adam Wolf
Category: Science
Difficulty: Moderate

When I was younger, I spent hours perusing Bill Beaty’s electrostatics web pages. At the time, I didn’t achieve any real successes trying to build his high-voltage contraptions, and so my interest waned.

Years later, I saw someone online use a soda can as a collector for their Van de Graaff generator, and all my childhood memories of futzing with styrofoam and foil came rushing back. I made my first sparks that afternoon, after a quick stop at our local surplus store.

Here’s the simple design I came up with after consulting several tutorials. Using this device, I’ve generated thick, bright sparks 3" long, and faint sparks 6" long. Hold your finger close to it in a darkened room and you will see an eerie blue corona around your fingertip.

How It Works

There are 2 types of Van de Graaff generators. This one uses the triboelectric effect, in which certain materials become charged by contact with other materials — like when you rub a balloon with your hair.

During operation, a motor and roller at the bottom of the generator drive a rubber belt around a glass roller at the top, which creates a negative charge on the belt. A metal brush transfers this charge to a soda can, which is able to store a large amount of charge because it is both hollow and a conductor. The belt meanwhile becomes depleted of free electrons and needs to be replenished, and so a second brush at the bottom pulls in charge from whatever it’s connected to.

Steps

Step #1: Build the base.

Stand the 3"×1½" PVC coupling on its wide end, and insert the 1½"×1¼" bushing. Cut a length of 1¼" PVC pipe about 2" long and insert it into the bushing. Don’t jam the parts together. Press-fit them just enough that they’re joined, but loose enough to disassemble.
Connect the tee to the 2" length of pipe

Conclusion

Operation and Experiments

To increase the stored charge, hold the bottom brush. You’ll get the biggest sparks by holding the back of your hand flat alongside the can, and if you point a finger near it in the dark, you may see the air glow blue.

Tape threads or tissue paper strips to the can; they should spread out and repel each other. Tape a bent paper clip or wire to the can, and instead of building up a charge, the end of the wire will create a small wind of ions. Blow bubbles or drop confetti near your generator and watch what happens.

Troubleshooting and Adjustments

Humid environments inhibit the triboelectric effect. Test-rub a balloon or a fleece blanket on your head; if it doesn’t generate static, it’s too humid. You may be able to get your Van de Graaff generator to work after blowing hot air through it with a hair dryer.

If it still isn’t working, remove the can and go back over Step 9 (assembly), checking the brushes and belt. Also try cleaning the rollers or replacing the rubber band. All working surfaces must be clean, dry, and free of oil.

Once the generator works well, cover the rim of the can with electrical tape and attach it to the coupling. Covering the can-opener marks increases the maximum charge.

Eventually, the Van de Graaff generator will attract dust, reducing its effectiveness. Wipe the dust off with a dry cloth to return the generator to peak ability.

This project first appeared in MAKE Volume 28, page 124.

6 Responses to Simple Van de Graaff Generator

kashyap on July 7th, 2012 at 8:09 am said:

im tryin to build 1 bt the problem is ven i give little tension the rubber band does not rotate plz help…

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Tim Lindop on August 26th, 2012 at 6:24 pm said:

I am trying to build one but can’t get the electrical tape to stick to the rotor shaft. The rotor shaft is about a third of an inch long, which I noticed is the same as the recommended one from Jameco. If I were to trim down the electrical tape as was suggested, there would be no length to attach the rubber band, never mind to make a crowned pulley. Recommendations?

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Karina on March 14th, 2013 at 5:07 pm said:

Hello, I am student and I am trying to do this project. My question is in terms of the measurements what does 1½’ mean what is the equivalence in inch of frac?

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- Erin O'Neill on March 25th, 2013 at 7:22 am said:
  
  1½’ means 1 1/2 inches. If you read through the instructions on the bottom, the fractions show up as they are supposed to if you are still confused about how you are supposed to read them!
  
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  Telstar on March 26th, 2013 at 10:22 pm said:
  
  Good thing you told everyone that … I was having trouble with the fractions…
  
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sean1t on May 16th, 2013 at 11:31 am said:

can I make the collecter with something not can or ball shaped?

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