■ FIGURE 5. The completed lightning
screen project.
construction of a lightning
screen — but which is highly
recommended for its
operation — is a variable
voltage transformer [VVT]
such as a variac, powerstat,
etc. The VVT allows full
control over operation of
the screen and can assist in
determining the correct
amount of ballast. Too much
ballast draws a near-zero
current and produces very
little sparking. A weak
ballast will fill the screen
with crackling discharges
but at the expense of
pulling an excessive current.
The VVT allows the
operator to find an
acceptable balance. Lacking
such a control requires
energizing the circuit at
full voltage. Although this
procedure can create
startling results, it is a
practice I choose to avoid.
Variable transformers
featuring both a voltmeter and ammeter are preferred over
the single or non-metered models. Unfortunately,
purchasing a dual meter VVT can be an expensive
proposition. Even a used double-meter model — if one
can be found — brings in big money. I surmounted the
problem by purchasing a 7. 5 ampere meterless VVT at a
hamfest for less than $10. I mounted it within an old metal
cabinet and added two inexpensive meters along with an
inlet, outlet, switch, fuse, and pilot light, for a cost of less
than $50. eBay is another good source for finding used
variable transformers.
■ FIGURE 6. A close-up showing
comparative sizes of the 16” and 8”
discs. Also shown are plastic retaining
clips to hold the disc in place. The
luminous glow paper behind the glass
disc provides the coloration.
rings can provide the electrical tinker with a superior
inductor core product.
A simpler and less time-consuming method is to
connect a 150 watt (or larger) incandescent bulb in series
with the transformer input line. Another approach is to
insert an electrical heating device (hot plate, toaster, etc.)
or similar resistance in the circuit to act as a ballast. My
project pulls between 5-7 amperes. No current control is
required when screens are powered by current limiting
ignition or neon sign transformers.
A piece of equipment not essential to the
■ FIGURE 7. An inductive reactance was placed in series
with the 120 volt line to control current draw. This unit
was once a component part of an old medical machine.
40 August 2009
■ FIGURE 8. An inductive reactance can be easily
constructed using readily-available materials.
