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Re: Tesla Coil Understanding

Subject: 
           Re: Tesla Coil Understanding
      Date: 
           Fri, 28 Mar 1997 13:47:44 -0800
      From: 
           Bert Hickman <bert.hickman-at-aquila-dot-com>
        To: 
           Tesla List <tesla-at-pupman-dot-com>
References: 
           1


Tesla List wrote:
> 
> Subject:
>         Tesla Coil Understanding (fwd)
>   Date:
>         Thu, 27 Mar 1997 20:55:50 -0700 (MST)
>   From:
>         List owner <listown-at-poodle.pupman-dot-com>
>     To:
>         tesla-at-poodle.pupman-dot-com
> 
> ---------- Forwarded message ----------
> Date: Thu, 27 Mar 1997 11:02:26 -0700
> From: Scott Taylor <staylor-at-ppco-dot-com>
> To: tesla-request-at-pupman-dot-com
> Subject: Tesla Coil Understanding
> 
>  I have read and enjoyed the pointed posts to this list and it has
> helped a
> great deal of my understanding of Tesla Coils.  One common thread that
> seems
> to be apparent, and this is what I am seeking comments from the list on,
> is
> that, in general, Tesla Coils are not all that well understood.  Would
> you
> (the list) agree or disagree?  Is the interaction between the primary
> coil
> and the secondary coil well documented and understood?  Is the
> efficiency of
> a Tesla Coil understood, i.e., the whole Tesla Coil system consumes
> power
> from the wall, how much of the energy "makes it" to the top of the
> secondary...or is that even a legitmate question?  Perhaps these are the
> incorrect questions...lets ask just one more in this fashion...What is
> NOT
> understood, documented in the literature, etc, about Tesla Coils?
> 
> Thanks much to all,
> 
> Scott Taylor
> staylor-at-ppco-dot-com

Scott,

WOW! 
Trying to answer this post could fill a book! The underlying principles
of coupled resonant circuits, transmission lines, and breakdown
phenomona are all quite well known and "mostly" understood by those in
the physics and engineering communities. In reality, there's not very
much mystery surrounding the coupling of energy between the primary and
secondary of a 2-coil Tesla Coil. A number of authors have excellent
treatments of dual-tuned, coupled resonant circuits (Terman, Skilling,
Smythe, and the Corums), spanning the lossless case to the more general
(and mathy) lossy cases. The theory, and the math, although tedious, is
quite well defined and has also been confirmed by numerous experiments
going back from Tesla, through spark radio, to today's experimenters on
this list.

However, what is NOT well known is the overall interactions which come
from the "non-linear" portions of the system (mainly the primary
spark-gap and secondary streamers). Although it's possible to predict
(in theory) what may happen, in practice the combination of linear and
non-linear effects typically combine in ways that are not (as yet) fully
predictable. Also, knowing that "optimal" perfomance should be
obtainable by quenching at a certain time is nice.... knowing exactly
_how_ to consistently do this would be even nicer! 

It's known empirically that some combinations of incoming ballast
inductance and resistance work better with certain primary-tank
capacitor combinations. If we then couple this to the "properly
configured" secondary:toroid pair we sometimes obtain "synergistic"
operation - long spark lengths with relatively low input power and
component stress. However, having a firm theoretical understanding of
just how/why this comes about, and how best to achieve it, is still the
subject of considerable mystery. The fact that experienced coilers get
to the point where they can design a "synergistic" system does not mean
we understand WHY. The interplay you see at work on this list is really
a combination of people experimenting and trying to make sense out of
the results. Sometimes its the other way around - formulating a theory,
then subjecting them to the acid-test of experimental reality. If we can
understand, in detail, how the critical elements of the system work from
a theoretical and practical standpoint, we should be able to design
better coils.

There's great difficulty in precisely measuring many of the parameters
of a Tesla Coil (input power, outpout power, efficiency, etc...), and
you'll find LOTS of opinions on how best to do these. In reality, most
coilers (if they measure anything at all!) simply look at analog meter
readings of input current and voltage versus output spark length to
judge "efficiency". While not scientifically precise, spark length vs
KVA IS a measurement that almost anyone can make without having a
laboratory of specialized equipment. While this doesn't exactly tell us
how much energy "makes it to the top", it DOES give us a relative
measure of performance that most coilers on this list can measure and
understand.

Scott, in the final analysis Tesla Coiling is a lot like peeling an
onion... there's always another layer below. Once you've answered one
question, another one emerges. But isn't it really more interesting that
way?? :^)

Safe coilin' to you, and have _fun_ searching for the answers!

-- Bert H --


If you're REALLY interested in the gory details, here is a partial
listing of potential reading material (available at larger technical
libraries). Some of these may also appear in the used book market
(Powell's, Advanced Book Exchange, etc...):

Breakdown Phenomena:
====================
Cobine, James, “Gaseous Conductors; Theory and Engineering
Applications”, Dover Publications, 1958, 606pp 

Loeb, L. B., "Basic Processes of Gaseous Electronics 2ed", U of
California Press, 1955, 1012pp 

Maxfield & Benedict, “Theory of Gaseous Conductors and Electronics”,
McGraw-Hill, 1941, 483pp 

Meek, J. M. and J. D. Craggs, "Electrical Breakdown of Gases", Oxford,
1953, 507pp

Spark-Gaps, Capacitors, High Power Electronics:
==============================================
Frungel, F., "High Speed Pulse Technology", Vol 3, Academic Press, 1976

Glasoe, G. N. and J. V. Lebacqz, “Pulse Generators”, Dover Publications,
1965, or McGraw-Hill, 1948 

Sarjeant, W. J. and Dollinger, R. E., "High Power Electronics", Tab
Professional and Reference Books, 1989, 392pp

Coupled Circuits:
================
Skilling, H. H., McGraw-Hill, "Transient Electric Currents”, 1952, 361pp

Smythe, William R., "Static and Dynamic Electricity, 2nd Edition",
McGraw-Hill, 1950, 616pp  (Very technical)

Terman, F., “Radio Engineer's Handbook”, McGraw-Hill Book Company, 
1943, 1019pp  (Excellent coverage of skin effect, coupled resonant
circuits)

Tesla Coils in General:
======================
Bylund, Duane, "Modern Tesla Coil Theory" (Excellent - easily readable)

Corum, Kenneth, “TC Tutor”, Book and SW (Excellent - more technical)

Couture, John - various books/design tools (such as the latest, JHCTES
V2.3) (Solid experimental information and good design tool. John's also
an active contributor to this list, BTW)

Potential Sources for the Tesla Coil books above:
------------------------------------------------
21st Century Books, 970-453-9293 (very highly recommended)
Tesla Book Company, 1-800-398-2056
International Tesla Society, 1-800-397-0137