lso minimizes the production of ozone--a gas created when high voltage causes three oxygen atoms to join
together. Ozone has a tart, sweet "electrical" smell, and is 100 times as poisonous as carbon monoxide. Beware: it
quickly causes headache, nausea, vomiting, and respiratory irritation. In addition to insulating all the exposed HV
areas, you should also operate your equipment with good ventilation if it produces any ozone.
Closely linked to ozone generation is corona leakage. It is produced by a charge being leeched off a highly charge
object by the air. That typically produces ozone. However, sometimes a device (such as a Van de Graaff generator) is
constructed specifically to display corona discharge, and insulating it would defeat that purpose. In such cases,
good ventilation is the only practical means of hazard prevention.
Ozone can also be created by arcing, which can occur anywhere. However, ozone production is not the greatest hazard
arcing presents. At 50Kv, a spark can arc between an uninsulated contact and your body if you come within 2 inches of
the contact. Arcing commonly takes two forms; directly through a capacitor's dielectric (as mentioned earlier), or
across the edges of a capacitor's plates to an adjacent plate. A snapping sound indicates the presence of arcing, so
keep your ears open.
Arching from the edges of a capacitor plate, or anywhere the shape of a conductor changes abruptly (such as the tip of
a nail) is called point discharge. It can be readily observed in a dark room at very high voltages,. Small, bright
blue pinpoint(s) are seen leaking electrons into the air, accompanied by a hissing sound and copious ozone production.
Once again, insulation and proper ventilation are the proper solutions to all these problems, and there are some
specialized techniques to insulate your capacitors and otherwise improve the safety of your high voltage projects.
Let's get to those now.
A key ingredient in a good assembly is a proper case. Your capacitor's housing must protect it against moisture, 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, 