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Re: High Voltage Output

Original poster: "Antonio Carlos M. de Queiroz" <acmdq-at-uol-dot-com.br> 

Tesla list wrote:
 > Original poster: "Chris Fanjoy" <zappyman-at-hotmail-dot-com>
 >    As someone relatively new to this hobby (still building my first TC) I
 > haven't fully grasped all the principles involved. One thing that has me
 > puzzled is this: what determines the high voltage output of a Tesla coil?
 > If not the step-up ratio of the coil itself, then how about:
 > -Firing rate of spark gap
 > -Size of tank capacitor
 > -Operating frequency of coil
 > -All of the above?
 >    Just curious, as this may be something to consider as I design my own TC.

Essentially, the ratio of the primary capacitance to the secondary
(distributed) capacitance. A classical Tesla coil is a pair of coupled
LC tanks tuned to the same frequency, one, the primary, with low
impedance, and another, the secondary, with high impedance. When some
energy is put in the primary, causing it to oscillate, the oscillations
gradually transfer the energy to the secondary, and after some cycles
all (or almost, allowing for losses) of it can be transferred.
Considering that the initial energy is in the primary capacitor C1 and
the maximum output voltage occurs if all the initial energy ends
in the secondary capacitance C2, the ideal voltage gain is sqrt(C1/C2).

The energy transfer tends to revert direction after it is complete,
returning the energy to the primary tank in the same number of cycles,
and the sequence repeats. It happens, however, that eventually the
primary gap ceases to conduct at one of the times when all the energy
is in the secondary system ("quenches"), and after this the remaining
energy is trapped in the secondary system until complete dissipation.

Curiously, as both tanks are tuned to the same frequency, and so
L1*C1=L2*C2, the gain is also equal to sqrt(L2/L1). If both coils
could be wound with the same geometry, this would be precisely the
turns ratio between the coils.

Antonio Carlos M. de Queiroz