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Re: ISEF display
Jeremy,
Good luck at ISEF. I saw an idea for demonstrating the "skin
effect" in
a physics demonstration book- you have different diameters of copper pipe
that are arranged coaxially, maybe six pieces in all, all soldered into
an endcap at one end and open at the other. The capped end is attatched
to one output of an RF oscillator. Little incandescent bulbs are attached
to each free end of the pieces of concentric pipes, and the other ends of
the lamps are connected to the remaining output terminal on the
oscillator. Ideally as an indication of the skin effect, the bulb on the
outermost piece of pipe will light up and the others will stay dark or
light very dimly.
I was thinking that your coiling needs (for the fair at least) would be
satisfied with a small simple tube coil, maybe with an 811 or two (very
cheap) or even some TV sweep tubes. There's not much noise or ozone, and
your primary voltage will be around 2000 volts, much easier to properly
insulate than 10,000. You can run such a little coil without a separate
counterpoise or dedicated RF ground. I had a tesla coil (sign-transformer
powered) in a science fair a few years back, and I recall that the judges
had a big problem with the neon transfomer. They did not, however, have a
safety problem with a 1500-volt capacitor charging supply which I also
had entered, which blew up aluminum foil sheets. So I think that while a
tube coil is not necessarily any safer electrically, it won't make the
judges as uneasy as will your big sign transformer. The same tube
oscillator would also suffice for the skin effect arrangement.
If you must shield the arrangement, that wouldn't be too hard with some
chicken wire. On the other hand, if you bring your million-and-a-half
volt coil in, you will obviously have a much more difficult task if the
shielding is required.
Carl