st 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 non-conductive mandrel or spool--ideally made of plastic or a glass rod
(be careful not to break a glass rod). Try to make the roll straight and free of lumps and wrinkles. When it's all
rolled up, secure it with plenty of tape. The author uses clear package-sealing tape for this. Now secure the
positive foil tab (assuming it's going to be for DC) to the mandrel using tape. Finally, coat the exposed ends with
an insulating product like silicone RTV.
The remaining foil connection tab may be reinforced by rolling it around a small metal dowel. A nail, or a cut-off
piece of 1/8-inch uncoated brazing rod is suggested. Apply glue to hold the assembly tog ether.
Foil tabs can be strengthened by adding "ribs" of adhesive from a hot glue gun. Similarly, the tabs can be made
tear-resistant by applying hot glue where they enter the capacitor.
Note most problems with this design come from particle contaminants that stretch a dielectric thin in spots where
they are trapped by the tightly rolled dielectric. Another trouble is inadequate edge spacing, causing arcing across
the ends. Careful planning and assembly will eliminate both headaches.
High Voltage Safety and Warning Label:
High voltage is considered any value over 500 volts AC or DC. When you attach a capacitor to
high voltage, you are multiplying its hazard many fold. There fore, experimenters must take extra precautions to avoid
painful shocks and possible electrocution. Here are a few guidelines to follow when working with high voltage:
Label your project in several location with: "Danger, High Voltage" where appropriate. Such
a warning label is provided here for you to copy (See Fig. A). Keep children, pets, and curiosity seekers away from
the apparatus. Cover all bare leads, wires, connection terminals, and possible points of contact with high voltage
putty or a cover fabricated from thick clear plastic.
Work in a dry location. Working in a damp basement of workshop courts disaster. Wear
rubber-soled boots or sneakers. Stand on a thick rubber mat.
Never put your b