The Turn Of The Century
Electrotherapy Museum
Tesla's Tesla Coils Article

 Three forms of 1890s Tesla Oscillators reproduced by Jeff Behary of The Turn Of The Century Electrotherapy Museum, 2004.

Tesla Coils:
Defining a Tesla Coil using Nikola Tesla's standards.

The modern definition of a Tesla Coil is drastically different than that which is represented
in Nikola Tesla's series of High Frequency patents.  To better understand Tesla Coils, and
how they operate it is vital to study the earliest working models of these coils created by
Tesla himself.  The following excerpts are from an article* written by Tesla in 1919, describing
the early forms of "universal" Tesla Coils.  These devices could operate on alternating or
direct currents, utilizing a variety of voltages from 110V to 220V.  The three color photos above
depict reproductions of three different styles of these coils.  The clickable thumbnail images on
the left will bring you to a photo gallery of images.  These coils consume from 5 - 20 watts from
a 110V power source and produce up to a shower of 4" sparks.  As seen from the photos,
these devices supply more than enough power for the average Crookes tube, yielding penetrating
Röntgen Rays - one of the many functions envisioned by Tesla for the practical use of these devices.

"... From the very beginning I felt the necessity of producing efficient apparatus to
meet a rapidly growing demand and during the eight years succeeding my original
announcements I developed not less than fifty types of these transformers or electrical
oscillators, each complete in every detail and refined to such a degree that I could not
materially improve any one of them today.  Had I been guided by practical considerations
I might have built up an immense and profitable business, incidentally rendering
important services to the world.  But the force of circumstances and the ever enlarging
vista of greater achievements turned my efforts in other directions.  And so it comes
that instruments will shortly be placed on the market which, oddly enough, were
perfected twenty years ago!"...

What are the components of a Tesla Coil?

"The essential parts of an oscillator are:  a condenser, a self-induction coil for
charging the same to a high potential, a circuit controller, and a transformer which is
energized by the oscillatory discharges of the condenser."...

How do Tesla Coils operate?

"The operation is as follows:
When the switch is thrown on, the current from the supply circuit rushed through the
self-induction coil, magnetizing the iron core within and separating the contacts of the
controller.  The high tension induced current then charges the condenser and upon
closure of the contacts the accumulated energy is released through the primary, giving
rise to a long series of oscillations which excite the tuned secondary circuit."...

How efficient are Tesla Coils operated by this method?

"Under favorable conditions an
efficiency as high as 85% is attainable, that is to say, that percentage of the energy
supplied can be recovered in the secondary of the transformer.  While the chief virtue
of this kind of apparatus is obviously due to the wonderful powers of the condenser,
special qualities result from concatenation of circuits under observance of accurate
harmonic relations, and minimization of frictional and other losses which has been
one of the principle objects of the design."

Are the interrupters of these apparatus a source of inefficiency?

"Contrary to what might be naturally
expected, little trouble was experienced with the contacts, although the currents through
them were heavy, namely, proper conditions of resonance existing, the great flow occurs
only when the circuit is closed and no destructive arcs can develop.  Originally I employed
platinum and iridium tips but later I replaced them by some of meteorite and finally of
tungsten.  The last have given me the best satisfaction, permitting working for hours and
days without interruption."

Behary Reproduction of 1kW Tesla Oscillator.


(C) Jeff Behary, 2004