dirt,
and accidental discharge. Plastic cases for dry capacitors are easy to make with acrylic sheets glued at all corners
with Silicone RTV. Oil-proof cases can be made for immersed models, but you will need to rough-up the plastic at the
sealing edges with sandpaper and use both a bonding and a second fillet glue coating for a liquid-proof seal. Metal
cases can be made from PC boards cut on a shear or large paper cutter and soldered at the edges. Copper roof flashing
(available at hardware stores) works well too. However when using metal always beware of contamination by solder
rosin, solder bits, and other crud, which can short out plate or otherwise reduce efficiency.
Whether a capacitor is enclosed or exposed, discharge paths must be wide enough to avoid arcs to the case, adjacent
plates, terminals, connections, or components. That is especially important in situation where conductors must be
left uninsulated. Note that the space from each plate to the edge of the dielectric must be wide enough to stop any
spark from "crawling" over the edge of one plate to another.
Power leads must be capable of withstanding the full voltage of the charge plus at least a 50% safety margin. TV
anode wire, which comes rated up to 40 Kilo Volt DC, makes great leads. Vinyl tubing or aquarium air hose may be
slipped over leads to increase their voltage rating.
Make sure the plates are securely mounted or they will tend to shift, or make a noisy rattle when used with AC. Glue
or compress the assembly to hold it secure. With regard to mounting, keep in mind that glues that dry by evaporation of
a volatile chemical might not set properly if "buried" inside an assembly away from air, and could thus become a
Rolled-up capacitors may be held securely by wrapping the interleaving layers of foil and insulator tight around an
insulating mandrel and then taping with a clear PVC tape. Where necessary, coat the ends with Silicone RTV. That
will eliminate end-arcing flash-over and corona loss. Alternatively, although is is somewhat brittle, 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 g