VDG ELECTROSTATIC GENERATOR
|(c)1996 William J. Beaty|
MAKE YOUR OWN SPHERE-TERMINALThere are a number of ways you can build a sphere terminal (also called a toroid or oblate)
Electrostatic Lightning-bolt Generators
1992 Walt Noon ppbk pp91
from the infamous Lindsay Books
ANCIENT METHOD FROM 1950s:Buy a steel world-globe. Cut a hole in the bottom. Sand off all the paint. A variety of various sizes of metal world globes can be found, including 1in diameter pencil sharpeners which are excellent for building ultra-tiny rubberband belt VDG machines.
BETTER: USE MIXING BOWLSPurchase two metal mixing bowls. Cut a hole in the base of one. Join the bowls rim-to-rim by winding black electrical tape around the rim several times. There may be some corona leakage from the bowl rims. This can be reduced by applying a thick (1/4") bead of silicone caulk to the outside edge of the bowl rims.
IMPROVED METHOD: BUNDT PAN(S)
If you're ambitious, you can increase the maximum voltage attainable by
the mixing-bowl sphere by removing the rims. Cut or grind them off,
grind and then sand the edge of each bowl so it will sit flat (test it
against a flat tabletop.) Be sure to file off all burrs from the edge.
Temporarily attach the bowls edge to edge with tape on the inside.
Obtain some adhesive aluminum foil tape from a hardware store. This is
foil-type duct repair tape with a peel-off waxpaper back. Lay down the tape and
burnish it down with a plastic spoon. Avoid making any creases.
Another way to connect the bowls is with conductive epoxy, or epoxy
followed by a layer of conductive paint or aluminum tape. Place the
bowls edge to edge
and wind a couple of layers of masking tape along the gap to seal.
Working through the hole, fill the gap with epoxy, then add a temporary
layer of tape over the epoxy to keep it from running too badly. You'll
probably have to do this in sections, letting one section harden before
starting the next. Remove the tape and sand down the epoxy. If you're
using normal (nonconductive) epoxy, paint the epoxy with a coat of
conductive paint (available from some TV repair stores and mail order
CONDUCTIVE PAINTVarious plastic globes can be found, and these can be coated with conductive paint. One type is G.C. Electronics "Nickel Print", Number 22-207. It is fairly expensive, but take a look at their Silver paint, whew!, like thirty bucks for a couple of ounces! Once source is Allied Electronics (mail order), see their Catalog site Note: the paint only needs to be very slightly conductive. India ink or a mixture of carbon black and wood glue will work. However, if you want to create high-energy sparks, the resistance must be low, therefore use metal. OR PERHAPS... use carbon paint for the major part of the sphere, then use rubber cement to burnish down a large disk of aluminum foil onto your onto your inexpensive globe. On the other hand, if you want your VDG to be entirely safe, use diluted carbon paint, that way the painful sparks will simply be impossible, and kids can put their hands on the machine in full operation without getting "zapped."
POP CANSCola cans have fairly smooth bottoms. IF you remove the pull-tab of two cans and tape them mouth-to-mouth with electrical tape, you'll end up with a very smooth metal object. You can use this to create a good VDG upper terminal. Take 12 empty cola cans, bind them mouth/mouth to make six pairs, then connect them side by side with tape and glue, so that you make a large cylinder with hollow middle. This forms your VDG terminal. As long as your upper VDG brush assembly remains entirely within the hollow part, the cans will function the same as a hollow metal globe.
PAPIER MACHE AND INKHere's an untried method for sphere construction. I found that india ink is a fair conductor. If you make a papier mache sphere from glue-soaked newspaper strips on a balloon, a coating with India Ink should make the surface become conductive. While the conductivity might be too poor to generate impressive sparks, it should serve well for e-field demonstrations (hair raising, etc.)
QUICK AND DIRTYContrary to what you might think, a sphere ISN'T required in order to make a passable VDG. All that's really needed is a metal shield around the upper pulley/comb assembly. This can be accomplished in a variety of ways: one inverted mixing bowl, a large metal coffee can, four 90deg elbow furnace ducts mated together (or eight 45deg ducts), a bent piece of sheet metal, etc.
I highly recommend taking the quick and dirty path, just to speed the
initial construction of your device. Don't let the unavailablity of a
perfect polished sphere stand in your way, use a rusty tin can at the
Some of the above methods give sharp edges which lead to severe corona
leakage and reduced generator voltage. One simple cure is: thick beads
of silicone caulk. For example, if you use an inverted coffee can as
a terminal, simply build up several layers of silicon caulk on the top
and bottom edges of the can. A 1/4 in. thickness is good. Use care
to avoid getting bubbles or leaving gaps in the caulk. Another simple
cure: adhesive foil tape from hardware stores, or even rubber cement
and aluminum foil. If you use rubber cement, coat both surfaces and
let the cement dry, then stick it on.
LANCE F. JERALE'S METHOD:Buy a large balloon from a party/costumes store. Cover it with many layers of papier mache' (made from newspaper strips dipped in diluted white glue, mix glue with an equal amount of water.) Many layers are required, otherwise the surface will be too flexible. When dry, remove the balloon, repair any folds and loose paper strips with more paper and glue, dry thoroughly, then cover the sphere with adhesive aluminum foil tape (aluminum foil duct repair tape from a hardware store.) Burnish it down with an old spoon, and you've got a beautiful silvery VDG sphere.
If you're ambitious, you can shape an involute hole in your papier
mache'. Build many layers on a partially inflated balloon. Keep them
wet and soft, push it in to form a deep smooth valley, arrange some sort of
bracket or dangling weight to keep the valley in place until the mache'
dries, then repair the creases and folds with scissors and more mache.
Lance Jerale managed to build a FOUR FOOT DIAMETER sphere using this
method. He used a partially-inflated weather balloon as the form. His
finished machine produced bright & wicked lightning discharges
approximately 3ft. long!
Giant foam-stack sphere, by Mark Massey
I am having fun with a home built van de graaff. I am building a sphere for the collector. It is of an unusual construction. first i layed out the shape and size on CAD (computer adided design). It is 48" in diameter and built up from rings of extruded polystyrene foam (pink house insulating foam).
Oliver Schaefer's mache' and plaster spheres