Tesla Coil Future Part I
From: Richard Wayne Wall[SMTP:rwall-at-ix-dot-netcom-dot-com]
Sent: Sunday, August 03, 1997 4:55 PM
To: tesla-at-poodle.pupman-dot-com; rwall-at-ix-dot-netcom-dot-com
Subject: Tesla Coil Future Part I
TESLA COIL FUTURE Part I.
In a TCBOR video last year John Freau gave a short ending editorial on
Tesla coiling. To paraphrase, John talked of current Tesla coiling and
how we are on the brink of new and exciting discoveries. John's
optimism port ends new discoveries and even radical departures in the
field of Tesla coiling. Many of us are independently researching our
own new ideas and are incrementally moving our field into unchartered
territory. More often than not, new discoveries are built on the work
of those who precede, us as well as, our contemporaries. So where are
For the most part, modern Tesla coiling is tied to 60 Hz alternating
current. It's cheap, easy and readily available. However, frequency
is a limiting factor. We try to get around this frequency limitation
with various devices and schemes such as rotary spark gaps and vacuum
tube cw coils, to name a few.
A second major problem is switching the TC driver. The vast majority
of time, unless its a cw coil, switching is by a spark gap. Gaps, as
we know, are extremely energy wasteful. But, they are rich in
harmonics and have very high dv/dts. A TC secondary or maggey
resonator is extremely efficient at instantly selecting and choosing
it's resonating frequency(ies) and harmonics from the infinite variety
offered by the spark gap driver. The rest of the SG energy is
Father Tom a few months ago wrote an excellent post regarding frequency
content of nonsinusoidal waves or portions of waves. Even a small
portion of a wave will contain immense information about its wave
component makeup and harmonics. For instance, the initial rise time of
a pulse, as well as the fall time to a lesser extent, contains vital
information about the harmonics of the wave even though its only a
limited part of the total wave. As an example, a square wave contains
in its sharp rise a whole series of odd harmonics.
Richard Hull and others are experimenting with alternate switching
devices such as H2 thyratrons to provide very fast rise times and
multiple harmonics for the resonator to choose from. He also
mentioned a reference on hard driving vacuum tubes to produce discrete
TC driving pulses rather than a continuous wave. The slope and shape
of the driving pulse determine the spectral content of the energy
available to the resonator. Could the slope be too fast or of the
wrong form? Sure, this would affect subsequent wave content and
harmonics available to the resonator. Eventually we will be able to
judge the exact frequency "needs" of the resonator. By constructing a
wave with an arbitrary wave form generator or other wave synthesis
generator, the exact frequency requirements of the resonator may be
provided with no wasted energy. Then we will be able to pump very
significant amounts of energy into our resonators. Ultimately we will
build super coils with totally experimentally derived synthetic wave
forms to drive them. These synthetic waves will have wave forms and
harmonic content that even spark gaps are incapable of producing.
As a result of these changes, 60 Hz AC in highly advanced coils will be
abandoned. Direct current will be the order of the day. And, large
amounts of energy will be provided to our resonators with resonant
synthesized wave forms.
Having made these statements, I do not totally predict the demise of
spark gap coils in the near future. Who can deny the almost orgasmic
rush that a new coiler experiences at first light with the raucous roar
and brilliant white flashes of a new Tesla Coil as it comes to life?
New coilers will continue to come into our field in the time honored
fashion of their predecessors.
Advanced coiling will change radically though. Coil configurations
will change. They already are. TCBOR resonators currently use smaller
and smaller capacitors. Eventually discrete capacitors may be
eliminated altogether. Steinmetz described a coil that used inductors
only to drive the resonator. Then, of course, resonators will also be
driven directly with synthesized wave forms.
Available materials and components are continually improving. I
currently use large bipolar transistors (dual and single modules) that
have huge power capabilities. They are diode protected and handle 200
A at 1500 V. Their rise time to 600 V resistive is 3 uS. It's a
little longer with reactive loads. Current limiting and rectification
can also be accomplished with these BPTs. Also, IGBTs are rapidly
coming down in price and their rise time is on the order of tens of nS.
Then there is the hard driven vacuum tube driver mentioned by RH.