s, use single-side board.
To prepare each board, start by etching away a 1-inch strip from around all its edges. That process can be simplified
by first masking off the strip, spraying the bare copper with an etch-resistant paint, removing the masking tape, and
Clean the board after etching, and rinse with de-ionized or distilled water. Thoroughly air-dry the sections, or use
a blow dryer. Attach strips of aluminum foil to each plate.
If you are building a multiple-section capacitor, connect the aluminum foil strips together as shown in Fig. 3 and
secure them using glue or nylon bolts at each corner. Spray the finished assembly with several coats of an insulating
product, or paraffin.
If you use the dimensions shown in Fig. 2and a 0.060-inch gap between plates, you can achieve a capacitance of 1.94nF
(1940pF) per section. When deciding on the gap width to use, keep in mind that the greater the space between
successive plates the lower the chance of arcing. For example, a 1-inch spacing gives you a 30% larger gap than a
20-Kv spark can jump. Insulation will further improve that margin.
The Stacked Sheet Design:
This type is virtually identical to our PC board capacitor, but it can be designed to handle considerably more voltage.
You simply substitute sheet plastic or glass dielectrics, and glue aluminum foil in place of the copper for each
section (refer to the PC board capacitor drawing in Fig. 3 as needed). All in all, it's an easier design to build,
as it does not involve the effort of etching copper, and you can continue to add sections to your original prototype
to increase its capacity as future demands require.
When building a large capacitor of this type, we suggest that you use nylon bolts at the corners to hold it all
together. The bolt holes should be pre-drilled before assembly, and all chips cleared away. Make sure the
plate-to-edge spacing is adequate for the voltage you will subject the capacitor to. Add extra spacing if you intend
to use bolts at the edges.
Glue foil carefully to the top of the first plate using a small amount of spray adhesive, Krazy Glue, or RTV
silicone. Press it smooth and let it dry. A photographic finishing roller is hand for flattening foil. Repeat the
procedure for the second sheet, orienting the foil connection tab in the opposite direction. Keep the plates and
dielectrics aligned as assembly proceeds. Repeat this procedure for as many sections as you want. Always keep the
final number of plus and minus plates equal.
Put an insulating sheet above and below the last plate and secure the assembly with nylon bolts. Do not over tighten
or the center of the assembly will "bow". Finally, clean the ends with a very small amount of isopropyl (rubbing)
alcohol and wipe dry. Smear a coating of silicone RTV over all the edges.
The kind of capacitor depicted in Fig. 4 can provide large capacitance in a small size. They are a little trickier to
make than stacked-section type capacitors, so you might want to try a few small prototypes first. The design uses a
layered approach (as shown), and we suggest using only one section as it is difficult to align and wrap multiple
sections. By contrast, a single section several feet long is not too unwieldy.
Aluminum foil works great in these capacitors. You'll find the oven/broiler type, with is heavy-duty foil, far easier
to work with than the plain variety. Polyethylene and Mylar are the most common dielectrics, but you can experiment
with other materials.
Looking at the figure, note the orientation and shape of the foil plated (A) and (C). They can be easily secured to
the dielectric (B) using double-sided Scotch tape. Note also the edge spacing. An outer covering of dielectric (D)
will prevent the finished capacitor from having a "hot" case, which might be a hazard. With those points in mind, lay
the foil out on a smooth sheet of paper, which in turn should be laid out on a smooth, hard surface to prevent
wrinkling. Carefully assemble the four layers as shown in the drawing. Strive to make them flat and smooth.
Warp the capacitor "sandwich" around a 