Tesla
Coil Paper and High Voltage Projects
(Updated May 2014)
I’ve always been interested in high voltage
displays, probably from watching lightning so often during summer thunderstorms
in Colorado. I had a particular interest
in Nikola Tesla, because our home in Colorado Springs was built on the top of
the same hill occupied by his Colorado Springs laboratory some 65 years
earlier. No one had built on that empty
lot until we moved there about 1964. I
was even the subject of a newspaper interview in the local paper, discussing
Tesla and his high voltage experiments.
I also thoroughly enjoyed a Tesla-themed conference at Colorado College about
1992. While I had some limited success
building a high voltage Tesla coil in high school, not until I had the time and
skills after graduate school could I really understand the design. Based on an air-coupled transformer with
resonant tuning, I developed the theoretical equations and initial conditions
that describe the Tesla coil. I made the simplifying approximation that the
conventional spark gap had a low impedance during its spark. In order to test my equations, I needed to
replace the spark gap with a transistorized component, which also allowed
operation at a low voltage. I was then
able to use an oscilloscope to measure the resulting waveforms, and of course,
the theoretical curves closely matched the experimental data. I built the low voltage Tesla coil using
enameled wire on PVC pipe, with an old AM radio variable capacitor and a simple
electronics breadboard. I wrote the
paper shortly after I moved to Colorado, and it was published in the American
Journal of Physics in 1992. I received
some inquiries from some college physics departments, and found out later that
they were using them in the student electronics lab courses. The paper was also selected by the editorial
board of the Journal as one of the best papers published that year.
It turns out that there are a number of hobbyists
who are interested in all things Tesla, and they have a newsletter. I subscribed for a few years, but simply did
not have time to contribute much. The
only mention was in a short note in 1987, where I noted the resemblance of this
grain silo to Tesla’s Wardenclyffe lab.
In addition to Tesla coils, I also put together a
Van de Graff generator, with help from my cousin Steve. I had some large hemispheres spun by a
machine shop and used PVC tubes and a latex belt. It was fun to play with, especially with
kids, but it never quite generated the spark length I thought it should. The photo shows one spark about 100 mm
long, and another about 50 mm long.
The air was always pretty dry in Colorado, so I left this with a friend
when I moved back to California.
My cousin Steve also gave me a neon sign transformer
that I used for a “Jacob’s ladder” in high school or college. The ladder was about 12” long, and the spark
travelled up the length in about 3 seconds.
This time exposure was published in “Science Probe” magazine in 1991,
although the slide was taken many years earlier.
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