The Wimshurst Influence Machine

By Jake von Slatt
Category: Electronics
Time Required: 2 weekends
Difficulty: Moderate

When assembling a proper laboratory, the gentleman or lady experimenter should be sure to include a Wimshurst electrostatic generating machine. This device will serve tirelessly in investigations into the field of natural philosophy, and provide interesting parlor games such as the “electric kiss.” Herein we will demonstrate the construction of such a spectacular device, with materials easily acquired from your local home center and hardware store.

Electrostatic machines create high-voltage charges without the familiar coils of copper wire, permanent magnets, and commutators found in conventional generators. They’re made of brass, glass, and wood, and they look more mechanical than electrical.

The coolest thing about them is that you can feel them working. As you begin to crank a Wimshurst machine, you can hear it crackle and hiss with energy, you can smell the sharp tang of ozone, and you can feel the hair on your arms stand up as the Leyden jars begin to charge.

Note: The one item I couldn’t find in a home and hardware store was the pair of O-rings. The total cost of materials was about $100, but most are common items, so a little scrounging and perhaps some dumpster diving should net you significant savings.

Steps

Step #1: Make a circle cutting tool.

This is a moderately difficult project. No single operation is particularly difficult, but a variety of techniques are involved. You’ll likely find the soldering to be the most challenging, but don’t fear, it’s easier than it looks. Practice on some scraps before each operation, and you should be fine.
To cut the two 14" acrylic circles, we first need to make a tool.
Cut a 12" length of ¾" square wood dowel. Drill a pilot hole near 1 end and press or drive a sixpenny nail through the stick so the point sticks out about ¼". Drill a second hole exactly 7" from the first and insert another sixpenny nail.
Use a fine metalworking file to shape the second nail as shown. You want to make a chisel point with a slight undercut on the leading face.

Conclusion

Operation

There are 3 variables you can play with: size of the spark gap, angle of the neutralizing bars, and switching of the Leyden jars in and out of circuit.

Start with the spark gap set to about 1", the neutralizers at 45° to the collector combs (90° to each other), and the Leyden jars disconnected. Turn the crank smoothly at a moderate speed. The electrodes should produce a thin blue spark. Look closely and you’ll notice that one end is brighter; this is your positive electrode.

Stop cranking and engage the Leyden jars. These can hold a charge for days. From this point on, consider the machine “hot” until you short the electrodes by simultaneously touching both with the tip of a screwdriver. Also be warned that Leyden jars can acquire charge just sitting there, so you need to discharge them this way each and every time before you touch the electrodes.

Turn the crank again. After several revolutions you’ll hear the neutralizing brushes crackle, you’ll smell the fresh scent of ozone, and — CRACK! — a strong blue spark will jump the gap.

Adjustments

Short the electrodes and reposition them a little farther apart. Crank some more and you’ll see a bigger spark. Repeat this procedure until you see multiple small sparks jump from one of the collectors, across several sectors, to a neutralizing brush. You’ve reached your maximum spark length.

After you find the maximum gap, you can adjust the neutralizing bars. Narrowing their angle from 90° to about 60° will increase the maximum voltage at the expense of a small decrease in current.

Maintenance

Your machine should require little maintenance, but may require periodic replacement of the belts and cleaning of the disks. Use only water to clean them, or rubbing alcohol if you suspect there is oil on them.

The Electric Kiss (and Other Entertaiments)

Wimshurst machines had a place in Victorian entertainment. After a fine meal, guests might adjourn to the parlor for games, discussion, and scientific demonstrations. One can imagine the visceral impact of the Wimshurst machine, with its spinning glass disks, electrical discharges, and the loud report of 6" sparks.

For the adventurous, in the right company, there was a demonstration known as the electric kiss. Two volunteers would stand on insulating surfaces. Each would touch one of the 2 charge collectors and then they’d slowly, without any other part of their bodies touching, bring their lips together for the inevitable “tingle” of electricity.

CAUTION: Demonstrate the electric kiss only with the Leyden jars taken out of the circuit, to avoid a painful jolt.