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



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 
we going?

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 
essentially wasted.

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.