Taken from KeelyNet BBS (214) 324-3501 Sponsored by Vangard
Sciences PO BOX 1031 Mesquite, TX 75150
August 28, 1990 courtesy of the Tesla BBS at 719 486-2775
Tesla Coil theory
Line voltage is stepped up by the high-voltage transformer
to a magnitude sufficient to charge the capacitor and force the
spark gap to break down. This action is repeated at the 60 hertz
line frequency. Efficient energy transfer is enhanced by choosing
a capacitor whose impedance is equal to that of the secondary
winding.
Essentially, the capacitor and tesla coil primary form one
pair of tank circuts: when the spark gap arcs, the momentary
short circut created dumps the capacitor's charge into the coil's
primary. The resulting L-C circut rings as the charge oscillates
back and forth between the capacitor and the coil. The oscillations
decrease in amplitude as the charge is dissipated by resistance.
The ringing generates what is refferred to as a "damped
wave". The next half-cycle of 60-hz recharges the capacitor,
starting the process anew. A train of hi-frequency waves, spaced
at 60-hz intervals, is the product.
Resonance must be achieved to effect ringing: this demands
the capacitor and primary have the same reactance:
X(L) = X(C) The circut resistance (capacitor, coil and intermediate
wiring) limits the overall efficiency of the tank circut. Efficiency
is rated in terms of "quality factor", represented
as 'Q':
Q = W(L)/R = X(C)/R
Increasing resistance reduces Q, thereby reducing efficiency.
The effect is minimized by winding the primary with a few turns
of heavy conductor, well-spaced, over a large radius form - the
larger the better. The capacitor size and construction also bear
upon Q: the physical size and area should be minimized. This,
however, works against large capacitance values and dictates
the coil be wound with more turns. The goal, then, is to achieve
a workable range of component specifications rather than to strive
for overly close tolerances. Coils often are wound with tapped
primaries to facilitate fine tuning.
The secondary coil is situated both electrically and physically
within the primary. The secondary and its discharge electrode,
generally a sphere or toroid, make up the second tuned circut.
The winding supplies inductance; the capacitor is created by
the electrode and the (earth) ground-plane. Air is the dielectric.
Most tesla coils employ secondaries of 1/4-wavelength at their
operating frequencies. This establishes a configuration with
maximum current at zero voltage with minimum current at the electrode.
This situation proves to be beneficial, in that it enhances coupling
with the high current primary, avoids arching between the primary
and secondary and generates the desired high voltage at the top
end. The "oudin" coil is a 1/2-wave variation on the
tesla coil. It possesses the essential tesla coil operational
characteristics, but it employs a horizontally placed secondary
with discharge electrodes at both ends and a primary at the center.
The oudin primary sometimes is merely a pair of taps on the secondary
(an autotransformer). The 1/2- wave arrangement affords a coil
with maximum discharge at each end and a virtual ground at the
midpoint of the winding(s).
If you have comments or other information relating to such
topics as this paper covers, please upload to KeelyNet or send
to the Vangard Sciences address as listed on the first page.
Thank you for your consideration, interest and support.
Jerry W. DeckerRon BarkerChuck Henderson Vangard Sciences/KeelyNet
If we can be of service, you may contact Jerry at (214) 324-8741
or Ron at (214) 484-3189
Nikola Tesla
Science
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