Build your own Van de Graaff generator!

Last year I set out to build a van de graff generator, and after a year of tweaking, I have something that works (most of the time).

The first step in building these is understanding the principles of how it works. I will attempt an explaination here, but please check out the wikipedia here.

The charges for this machine accumulate on smooth conductive surfaces, which is the reason for the large metal globe at the top. Generally, the larger the globe, the higher the voltage. Inside the tube, there is a belt with 2 rollers. The belt is made from some electrically neutral material that is also an insulator (latex). The rollers are made from materials that have opposite polarizations in the triboelectric series. I chose aluminum(+) and silicone rubber (-).

When the belt comes in contact with one of these materials, electrons are either pushed to one side of the belt, or pulled from one side. In the case that electrons are pulled from the other side, the metal brush is there to provide replacement electrons. (the reverse is collecting the extra electrons). The belt moves along over the roller, and eventually seperates from the roller. When the belt is seperated from the roller, it will then have a charge on the outside of the belt. (for those concerned about the conservation of energy, dont worry. The work of seperating the clingy-belt from the roller equals the charge on the belt.)

A couple of mechanical challenges when building this:

• Attaching the bearings to the pvc pipe so they do not move.
• keeping the belt on the rollers
• keeping the brushes in place
• attaching the bottom roller to the motor

These are not really challenges for those that are mechanically inclined, but I found mighty-putty to of use in a couple of places.

Lets start with the metal globe at the top. This is essentially 2 14" steel salad bowls from ikea. a hole is cut in one of them for the pvc pipe to fit into, and they are taped together inside and out with aluminum tape. after you cut the hole, use a file to take off any sharp edges with a file.

The globe will be detachable, and connected to the brush by alligator clip. The wire must be inside the globe; The reason being, that the globe becomes the center of an electric field. If it has conductive points on the outside of the globe that are not smooth, they will spew electrons in a process called corona discharge. What you really want is electrical breakdown, which is more impressive.

Get a PVC pipe, and cut to about 4 or 5 feet. (if you have high ceilings, use a 6 foot pipe)

Cut a U shape into each end to mount the bearings on. Make sure the u-shaped cuts are lined up, which will line up the belt rollers for less friction. The bearings should fit snugly, so they do not vibrate.

Keep in mind you will be putting the metal globe over the top roller. For that reason, I used mighty-putty on the top roller to attach the axle to the bearing:

To make the roller, I used a 5/16" x 6" carraige bolt as the axle. For the top roller, I cut off the head. The bearings are held in place by bolts. (btw, axeman is a good place to get cheap bearings) The roller was made from a rubber sanding drum drill attachment, which was cut to size, and then screwed onto the bolt. The drum is then wrapped with electrical tape (or any tape you like) to give it the right shape. You want a "crown" in the middle of the roller, as the belt will naturally tend towards the center of the crown. (this is how you keep the belt on the roller)

The bottom roller (above) has an extra rubber roller with a notch to hold the drive-belt.

Aluminum Tape, usually used for ventilation ducts. Used to cover the bottom roller, and seal the globe halves together.

Silicone tape, used for plumbing, used to cover the top roller.

A toilet flange holds the pvc pipe upright. This is bolted to a wooden base, purchased from the IKEA damaged goods section. The brushes are made from braided copper grounding wire. Aluminum tape holds the brush in shape, and a screw/washer attaches it to the pipe, allowing you to align the brush before assembly.

The bearings for the bottom roller are held in place by plastic inserts.

The latex belt is made from one of those pilates yoga straps, but get the heavy-duty-tension version, for more durable, thicker latex. After the rollers and the bearings can be mounted, you will have an idea of how long to cut the belt. Make the belt 10% shorter than it needs to be, so that it will stretch and have some tension when it is on the rollers.

Use rubber cement to glue one end to the other. Cut on the diagonal for a stronger bond and less of a chance it will catch on a brush. When you put the belt on, make sure it is facing in the direction in which the seam will not catch on the brush.

Next, the electronics

Go to axeman or other surplus/hobby store to get a 120V AC 2-pole motor. Most hardware stores will have dimmer switches. You can buy 3-prong plugs and wire, but most likely you have this already. Be sure to look up which wire is hot, neutral, and ground. The hot should go to the switch first.

The wire on the left leads to the bottom brush. The right side attaches to the grounding leads on the other components.

The aluminum plate keeps he motor in place, acts as a heat-sink, and is conductive for grounding.

I attached the drive-belt-pulley with mighty putty.

Accessories:

You can use smaller serving bowls to make an electrode. drill a hole for a conductive handle, and attach handle to grounding wire.

With some aluminum tape and a jar, you have a Leyden jar. This will make the sparks 50% more painful.

Well, once you are finished, show it to your friends after they have had a couple, and they will be more likely to volunteer for shock therapy.

Server cooling fan becomes ugly lawn ornament

So, you may think that I have too much free time, but the thing is, I like to tinker.

Here is a server fan turned ugly lawn ornament that will blink 2 red LED's when the wind blows faster than 5 mph (estimated).

If you happen to have one of these cooling fans (which you probably do, if you have as much outdated technology as I do), take it out of the computer case, and remove the plastic around the circuit board (wear goggles, plastic pieces will go flying everywhere). If you have outdated technology that may still be useable, consider donating it to this charity for re-use.

On the circuit board, you will see 3 gobs of solder that are a little bigger than the other gobs. use a knife to cut into the circuit board around these gobs, to prevent the electricity from leaking to other components on the board.

solder a wire to each one. (come to think of it, solder first and then cut. then you don't have to worry about your pathetic messy soldering job messing things up.) Attach 2 led's to each pair combination of wires, and determine which pair gets the most blink. with 3 wires, this will be 3 combinations. (n^2 + n)/2 = 6, but /2 since ba=ab. maybe you use 4 led's and all 3 wires?

Next, get a 2-liter plastic bottle and a glue-gun. Cut out the smooth mid-section of the bottle. Divide the width of this (the circumference of the bottle) by 7 (the number of blades on the fan). Cut the curved plastic into 7 equal rectangular strips. Next, figure the shape of the blade as something similar to what is pictured below. The reason the blade must be thinner at the edge has to do with the pitch angle. The angle of attack from the point of view of the wind must be the same for the whole blade. This varies as a function of (distance from center) * Pi * (rotational interval) There is an interesting video about how to make one out of pvc.

Use the glue gun to adhere the blades to the fan. make sure the straight edge is perpendicular to the tangent of the center circle (i.e. the blades are pointing straight out)

Glue-gun a stick to the back circuit board, and walla! a lawn ornament that is guaranteed to embarrass whoever you live with.

DIY windbelt with Wood and Duct Tape!

If you have not heard of the wind belt, read about it here.

I wanted to make one of my own, so I set out to build one on my own out of wood, duct tape, copper wire , magnets, and carriage bolts.

This first image shows the first material I tried - duct tape (aka duck tape, gun tape, handyman secret weapon)

I could not find a store that carried the Mylar-coated-taffeta that the video recommends, so I had to resort to trying a plethora of other materials. (to name a few: polystyrene ribbon, packaging tape, latex, scotch "extreme" tape)

I found that the material has to have the right balance between elasticity, density, and plasticity to be a candidate for this device. The latex fluttered a great deal, but the range of motion was too high. The extreme tape did not have enough motion. The duct tape worked well, but the material I finally settled on: gorilla tape in the 1" roll. I had to put two pieces together with the sticky sides facing each other. (I still plan on trying out the taffeta, once I find it...)

The support structure is about 5 feet long, 5 inches wide. There are 2 clamps to hold the tape. a clamp on 1 side has longer carriage bolts to adjust the tension. I found that one needs an even tension across the belt to get it to vibrate.

There are many factors in this vibration system: the tension, the placement/mass of the magnets, the mass/length of the band, the length of the band, and the resonances of the support structure. I'm sure you could apply some string vibration equations to calculate your ideal tension and length. I chose to spend hours in a windy basement with a wrench. Besides, I forget the name for this type of motion, but the 1 dimensional Helmholtz equations do not fully describe it. In addition to a propagation along the band, there is a side to side wobble, like the Tacoma Narrows bridge.

I already had the button magnets, which I got for another project here. I had to wind the coils myself. The wire - I got at Axeman for $20. You can also get it from guitar-part stores... like here .

Once you wind the coils, you need to solidify them - I soaked these in a bath of molten beeswax/paraffin for an hour or so. Once you get your coils solidified, you can solder on leads, and attach whatever led's / rectifiers you have in mind. I could not get enough voltage as of yet to power any low voltage inverters I had laying around, but once you figure the right circuitry you could most likely power a light, recharge a battery. Maybe a couple of these could run a wireless repeater? I have it hooked up to 4 LED's (2 for each coil). The reason: the electricity coming out of the coils is AC, alternating current. LED's only conduct electricity in one direction. If you attach 2 LED's in opposite orientations to a coil, together they will conduct both currents coming out of the coil (one for +, one for -)

I don't have a use for this ... but it is kinda cool to have. If anything, it is entertainment for the neighbors when they see me running back and forth in my backyard in the middle of the night, holding this big wood thing with blinking lights.

More pictures:

The top non-adjustable clamp:

The "bridge", to adjust the length of the belt:

4 LED's in the lamp enclosure: