This class teaches us to look at energy transfer methods and how many ways we can get to electricity. For my midterm I’m looking at one of the earliest forms of mechanical to electrical energy: Forced charge separation and resulting electrostatic discharge (ESD).
I am making a replica of the Wimshurst machine, following the instructions from Make magazine vol 17 on the blog of designer Jake von Slatt.
Because of the lovely sparks ESD devices make, I’m naming this project Fun-Spark (in honor of SparkFun). Briefly, the machine works as follows:
A hand crank moves metal disks past one another at speed, and stores the resulting charge imbalance in a capacitor/battery (called a Leyden Jar ) to be released by completing a simple circuit, making brilliant sparks if the circuit is completed through the air.
As you can see from the diagram above, there is no ground in this circuit. Circuits like this can generate high voltage (kV), which is dangerous if a large capacitor is used – a 55 gallon drum Leyden jar could easily kill someone. Mine will be smaller…much smaller. See this tutorial on capacitance for an interactive look.
But Allison, you ask, how can you just move a charge imbalance around? Doesn’t a charge induce the opposite charge in its surroundings? Isn’t that how the Leyden jars work in the first place?
Well I can’t deny it, that’s all true…let me explain a bit more about the machine. The trick to this machine is its two neutralizing rods set at right angles to each other, one per disk. This divides the wheels into four quadrants. The rods are the closest thing to a ground in this system, but they do not work the way a common ground does. Instead, they essentially short circuit the wheel they are attached to, zeroing at the charge on one side. But the other side is still charged. Remember the wheels move in opposite directions. As a charged sector goes by wires connected to the Leyden jars, they also induce a charge in the Leyden jars. Voila! We’re not violating the charge induction at all!
I will use the instructions and materials list from the blog to build, with minor modifications. The provided example used some scavenged parts and innovative workarounds – but given the materials and machines available at ITP, the process should be simpler.
Here is some background on the history of the Wimshurst, how sparks propagate via electrical breakdown of gas in the air, and a music video by Arc Attack to remind you that high-voltage sparks are AWESOME.
Materials and task list with minor modifications:
Cut 2 acrylic disks.
Attach the pulleys to the disks.
Cut the sectors.
Attach the sectors.
Prepare the drive pulleys and crank.
Cut and drill the disk supports.
Build the base.
Make the charge collector combs.
Prepare the charge collector mounts.
Make the discharge electrodes.
Fabricate 2 neutralizing brush supports
Fabricate the Leyden jars and shunt.
Mount the discs and drive line.
Align the disk and collector supports
Install Leyden jars and charge collectors.
Install discharge electrodes and neutralizing brushes.
Mount the Leyden jar shunt and add finishing touches.
Carpenter’s square, small
Epoxy, cellophane tape
Hacksaw, with fine tooth blade, coping saw, and miter box
Hobby knife, scissors
Metal files, fine metalworking, round (rat-tail), and flat crosscut intermediate (bastard)
Miscellaneous screwdrivers, and small pliers
Power Drill, and bits: 1/8″, 5/16″, countersink, and multi-step bit
Sandpaper, 400-grit, #00 steel wool
Screw tap, and handle, #6-32
Solder, rosin core
Tape measure, ruler
Fluorescent lamp protector sleeve for the Leyden jars
Staircase balusters (2) for supports for the rotating disks
Brazing rod, 1/8″ bronze from a hardware store or welding supply shop
Driveway marker rod, fiberglass, 5/16″ diameter
Tubing, 3/8″ OD thin wall, brass, 3′ section
Tubing (2), 3/8″ OD thin wall, brass, 6″ lengths
Pulley wheels (must be plastic)
Lamp chain pull balls (2), large, brass for the Leyden jar shunts
3/16″ Lexan enough to cut two 14″ circles.
Rubber feet (6)
Pipe hangers (2), 1″, copper Found in the plumbing section, they’re copper-plated steel.
Nuts (2), small, brass ball caps for the electrodes. Found in the electrical section, they’re commonly used to secure the top of brass outdoor lighting fixtures.
Screws (2), 2″ drywall with large washers
Casement window crank
Lamp finials (2), 3/8″ threaded for the charge collectors
Lamp finials (2), brass for the brush supports. These have a 3/8″ threaded hole in one end and a small hole in the other.
Screws (2), #8-32
Washers (2), flat, rubber
Threaded collars (2), 3/8″
Lamp nipples (2), 3/8″, 1″ long
Lamp washer nuts (2), threaded
Lamp finials (2), brass, with ½” ball end ½” ball end
Dowel, ¾” square, 12″ length or equivalent scrap. Pine works, but hardwood is preferable.
Nails (2), sixpenny
Milk jug, plastic
Bolt, 5/16″ with large (fender) washers
Foamboard, scrap about 15″ square
Alligator clips (4), and copper braid or solder wickfor the neutralizing brushes. Try RadioShack.
Wire, bare copper, 3′-4′
Closet pole mounting sockets (2), plastic
Setscrew collars (4), 5/16″ with setscrews for the axles/shafts
Setscrews (2), #6-32 for the neutralizing brush supports
O-ring belts (2), rubbber McMaster-Carr part #94115K259 (http://mcmaster.com), $15 for 8
Wire, 14 AWG solid copper, about 12″ length
Wood screws (2), small, brass