paraffin
(with a a puncture voltage of 250 volts/mil) is an excellent insulator for the ends of rolled-up capacitors and the
edges of flat-plate type capacitors. If you want to use melted paraffin wax, heat the wax only in a double-boiler
pan, since if it gets too hot it can catch fire. Be sure to apply several coats, allowing the wax to harden between
each coat. Liquid electrical tape also makes a great end seal, however it is somewhat hard to find. Try mail-order
distributors for that product.
High voltage terminals for your projects can be made from plastic rods drilled through to accept connection wires. You
may add a nut and bolt on top for convenience. However, beyond about 3,000 VDC this method suffers from point
discharge. Metal balls make good terminals. Clean them up with a wire brush or steel wool to eliminate rough spots.
The author uses fishing floats covered with aluminum foil or nickel print paint for up to 10KvDC. Split the bobbin
first with a razor blade, remove the line holder and spring, and glue it together again with epoxy.
Furthermore, as you work, keep all materials as clean as possible. Not only will your work have better appearance,
but arcs and burn-throughs due to contaminants will be prevented. High voltage easily tracks along dust, surface
contamination, and even finger oil (which contains salt). Also, we shall refer to a "section" as consisting of two
conducting plates with an insulating dielectric between them.
By now, we hope you have a good understanding of the principles and techniques involved in making your own capacitors.
Without forgetting safety, let's talk about how to build some simple capacitors, any of which can be modified for
A Leyden Jar Capacitor:
Leyden Jars are one of the first types of capacitors made, having been invented nearly two and a half centuries ago.
Their development was first recorded in 1745 by Ewald von Kleist. In 1746, Pieter van Musschenbroeck of Leyden,
Holland, experimented further with the invention. We can build our own modernized units with a gallon-size
wide-mouthed mayonnaise jar. The project only cost about $2.00 and is good to at least 10 KvDC at 2.5 nF. Units we've
tested at 15 KvDC did not fail; at that voltage, the capacitors stored just under 1/3 joule each.
First select a jar without bubbles, cracks, or blemishes and that has a mouth large enough to comfortably slip your
hand through. Next, carefully clean it out. You'll use aluminum foil inside and out as the conductive plates (see Fig.1).
Cut a foil disk 1-inch bigger that the bottom of the jar. Now coat the dull side of the foil and inside jar bottom
with a thin, even layer of rubber cement. Let both dry for 10-minutes, and press together. Smooth with firm hand
pressure. Avoid excess wrinkles. Do the rest of the inside except the top inch of the bottle using three of four
pieces of foil. (It is easiest to do the plate in pieces instead of all at once, since rubber cement "grabs" and it is
difficult to reposition the foil once contact has been made.) Now do the outside foil plate in pieces, leaving the
top inch bare. Check the foils with a continuity tester to determine if the pieces are in good electrical contact.
Areas of foil not in contact can be bridged with strips of foil or nickel-print paint.
For the top cover, cut two disks of clear plastic, one slightly smaller than the rim, the other 1/4-inch larger than
the rim. Glue the two pieces together to form a plug. Drill a 1/4-inch hole through the plug's center. Cut and
insert a length of 1/4-inch (outer diameter) metal rod or tubing through this hole. Attach a ball to its top, and
solder a wire or small-link chain to its bottom. The wire must make good electrical contact with the foil. Let the
assembly dry for a day with the cover off, to allow vapors from the rubber cement to dissipate, then cement the cover
on with silicone or Krazy Glue.
Some nifty low inductance capacitors can be made from pieces of copper-clad epoxy circuit board (see Fig.2). For a
simple two-plate capacitor, you can use one double-sided sheet. For multiple section