There was a time I used to brag that I could get a Van De Graaff generator running in a rainstorm. This was a bit of hyperbole, of course but I do have to say that I got pretty good at operating a Van De Graaff generator (VDGG from hereout) when I worked for a science museum. However, my experience was not typical for Van De Graaff users – more often that not, most VDGG’s are rolled to out to be used for one day in the Physics class. They are operated in 2-4 classes during that day and then rolled back into storage. My high school physics teacher, not the most comic of science teachers, consdiered the use of the VDGG and raising up a student’s hair to be ‘obligatory’ for the class.
This limited usage, however, may mean that many teachers don’t really get an idea of what can go wrong with their machinery. Especially when the VDGG is being used by a middle school or elementary school teacher who may not have the experience needed to run the VDGG proeprly.
The following is a list of things that can go wrong, how to diagnose them, and how to fix them. It is by no means comprehesive but should get you the opportunity to operate your VDGG successfully.
These are the problems that can spell major problems with the VDGG’s operation. This list is not going to include things like ‘plug ripped out’, ‘motor died’ or other errors. But will cover problems that will need fixing or replacement parts.
- Dents in the Dome Ball. Electricity likes to go to a sharp point. You may notice that the discharger included with the VDGG is a metal ball. This is because electricity has a hard time travelling to surfaces like that so the result is a big loud discharge. However it does like travelling to sharp points – you can discharge the electricity on the ball with the needle poking thing on your Swiss Army Knife – it won’t make a sound! WHy is this important? Well when in storage the VDGG can get banged around in tight science room storage areas and often the ball may fall from the VDGG tower. If it gets a dent that makes a nice sharp point that the electriticy can discharge from. If you get a large dent (1″ or mnore) you may not get any charge on the ball. You can try banging it out, but sometimes that just makes more mini dents. You may have to replace the ball. To prevent this: Remove the ball from the VDGG when transporting it or when it is in long term storage. Keep it in a plastic bag if possible, possibly with a dessicant pack.
- Dried, Cracked Belt. OK, you put something made of rubber (the belt) under tension in storage for a year and you a suprised it might dry out? If the belt gets to this stage there is not much that can be done. You will need a replacement belt. To prevent this: Unsecure the roller and belt from the top and gently bring it down the tube. The cover the tube with plastic. Don’t store in an area that is too dry or too wet.
FIXING THE VDGG
Almost all VDGG issues can come down to ‘no static electricity generating on the ball’. So here are the things you should check to make certain everything is working properly.
- Comb to Ball connection: The comb at the top of the tube should have a couple of leads leading off it. Those leads should be touching the metal of the top ball. They can get bent in ways that cause them to not make contact. Adjust them.
- Top comb not gathering charge: If you take the ball off the VDGG and put the tips of your fingers 1/2″ above the comb/brush at the top of the VDGG tube. You should feel the charge coming off the comb and into your fingers (its harmless). If you are getting this charge but no charge on the ball you need to re-do step one on this list and make certain there is contact, or check the ball for big dents. If you are not getting charge from the comb there is another problem that will need solving. The first thing to check is the position of the comb. The comb canb’t be too far away from the belt or too close. Typically the teeth of the comb should be 1/4″ from the belt. If they are touching the belt it will not gather charge, too far and the charges won’t make it. Adjust the comb until you feel the most charge you can get. If you still are not getting any charge there is another issue – but keep in mind this adjustment will fix a lot of issues with most VDGGs.
- Belt or tube is dusty/dirty. Sometimes VDGGs get left in storage with the ball removed but no dust cover over the tower. This or oother circumstance may lead to the belt getting dusty. You can check this by running your finger along the belt. If it gets a coat of dust, it will need to be cleaned. This will involve rubbing alcohol and lots and lots of cotton balls.
- Bottom comb not tranferring charge to belt: This may be due to the same issue as the top comb: It needs adjusting. This shouldn’t have to be done often but it will need it sometimes. This is tricky because adjusting the bottom involves removing the tower, making the adjustment, then replacing the tower & belt. Its a pain.
- VDGG Running too fast: Some model VDGGs were designed to be run with a variac of some sort and so if plugged directly into the wall and switched on they run at top speed. This can mean the belt will waver and buckle, losing its charge from toucing the walls of the tower or itself. It can actually run so fast the charges get pulled off or never get a chance to get on.
- Its all about the weather: Its a simple rule: you just don’t get much static electricity on a humid day. Usually some VDGGs can overcome the bad weather conditions to provide a bit of static generation, but sometimes the humidity or rain can prove to be too much.
I GET CHARGE, BUT CANT RAISE PEOPLE’S HAIR
OK, so you can a satisfactory pop from the discharge, you can make puffed rice fly, and the ball repels those mylar strips, but you get someone touching the ball and nothing happens?
Well, sometimes its the wrong kind of hair (curly hair does not work well), and sometimes you forgot to un-ground your volunteer. If the volunteer is still touching the ground the static charge will go over their body and into the ground. No good. The charge needs to build on their bodyt in order to repel their hair. Have the volunteer stand on a platform that is not conductive (i.e. no metal chairs) so that the charge can properly build. Have fun.