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Re: What IS special about a Tesla coil?
At 11:38 AM 4/19/00 -0600, you wrote:
>Original Poster: "Benkanosan" <benkanosan-at-townsqr-dot-com>
>
>Dear Terry and Bob,
>Following your e-conversations is a great educational experience for a novice
>coiler, but it's like sneaking into a lecture on tensor calculus when you've
>only just completed algebra one! I want to assure you that I, at least one of
>your gallant fellow coilers here on the list, am not an electrical (nor any
>other) engineer - and if I did have a functional Tek scope at this stage
of my
>coiling - oh, coiling were Paradise enow! (Pardon my inexcusable literary
>allusion - it's my poor defense against the swarming masses of you-all
>engineering geniuses). But a central and pivotal question jumped out at me in
>the most recent cited interchange; I think Bob asks: "WHAT IS SPECIAL ABOUT A
>TESLA COIL?" Yes! Isn't that what all coiling is about, after you get
through
>the cow manure, the horse manure, and the rabbit tracks through it?
[Credit for
>that colorful reference to an old desert rat (who died several years later
>searching for the Lost Dutchman gold mine - his life's dream; some search for
>lost gold mines, others dream of building the perfect coil!) with whom I was
>lucky enough to share a campfire and some beans in the high desert country
>outside of San Berdoo many (many!) years ago.] But, a parenthetical
digression
>is as annoying as any other, so let me continue: And since the question is
put
>so succinctly now, what is the answer - in the broadest terms? I make the
>following proposal, introducing a new acronym into the already bewildering
maze
>of abbreviations, initials, jargon, and other shorthand that I have read here
>on the site. The acronym was born out of Bob's question and a small flight of
>fancy. I imagine myself sitting in a lecture hall, all dark brown wood and
>uncomfortable pews, the afternoon sun lighting motes of dust that glint,
>hovering like tiny diamonds in the air. (I know you engineers need some of
this
>- so read on!) At the chalkboard in the front of the room is a dark-eyed.
>fierce man, furiously scrawling symbols and equations, stirring up even more
>clouds of dust. The swirling white lines and bizarre symbols he creates on
the
>board are dazzling, but their meanings are, to my unlearned mind, recondite,
>occult, overwhelming. I impulsively raise my hand - and now it is too late to
>withdraw it back to comfortable anonymity - the movement has already
caught the
>lecturer's eye! He stops, and with obvious pique, curtly nods his head at my
>raised, now almost trembling, hand as he puts down his chalk and takes two,
>slow, measured steps to the edge of the podium. He is not a large man, but he
>looms over me, a giant. He is terrifying. But his face changes, becomes
>gentle, concerned. He actually smiles. He speaks, a soft, well-modulated
>baritone, "Yes?" This one simple word projects interest, compassion, focus. I
>swallow hard and try to avoid looking directly into the bright intelligence
>that streams from his eyes. Again I swallow once, twice, and then manage to
>croak, "Dr. Tesla, what is SPECIAL about a Tesla coil?"
>My acronym: WWTS - What Would Tesla Say?
>Well, guys, please help me here, what WOULD he say? WWTS?
The main purpose of my coil is to demonstrate a great electrical
disturbance, that is, it produces large sparks and sheets of electrical
fire. What is "special" about my coil, is how this feat is accomplished.
Other scientists may fill volumes trying to describe the operation of my
coil. In fact, the operation of my coil may be a great mystery for 100's of
years. I will reveal to you, in just a few words, the basic concepts of my
resonant coil:
"The magnitude of the resonance effect depends, under otherwise equal
conditions, on the quantity of electricity set in motion or the strength of
the current driven through the circuit. But the circuit opposes the passage
of the currents by reason of its impedance and therefore, to secure the
best action it is necessary to reduce the impedance to a minimum. It is
impossible to overcome it entirely, but merely in part, for the ohmic
resistance cannot be overcome. But when the frequency of the impulses is
very great, the flow of the current is practically determined by
self-induction. Now, self-induction can be overcome by combining it with
capacity. If the relation between these is such, that at the frequency used
they annul each other, that is, have such values as to satisfy the
condition of resonance, and the greatest quantity of electricity is made to
flow through the external circuit, then the best result is obtained. It is
simpler and safer to join the condenser in series with the self induction.
By taking a coil with a very large self-induction the critical capacity is
reduced to a very small value, and the capacity of the coil itself may be
sufficient. It is easy, especially by observing certain artifices, to wind
a coil through which the impedance will be reduced to the value of the
ohmic resistance only; and for any coil there is, of course, a frequency at
which the maximum current will be made to pass through the coil.
As regards the rise of potential through resonant action, of course,
theoretically, it may amount to anything since it depends on self-induction
and resistance and since these may have any value.
Thus coils of the proper dimensions might be connected each with only one
of its ends to the mains from a machine of low E.M.F., and though the
circuit of the machine would not be closed in the ordinary acceptance of
the term, yet the machine might be burned out if a proper resonance effect
would be obtained."
And that, sir, is what is "special" about my coil!
Nikola Tesla, February 1893