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Re: 2 questions on resonance
Tesla List wrote:
>
> Original Poster: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
>
> Dear all,
> After reading the responses on resonant rise, I would like
> to ask why it is said that resonant charging allows one to suck more
> power from a NST? I suggest that if that were true, one could set the
> gap wider than for a non-resonant situation and still have the gap
> fire at the 2Fmains rate. Any comments?
>
> Malcolm
Malcolm and all,
One can! Probably the best analysis of this was done by Glasoe in "Pulse
Generators", section 9.5 (AC Resonant Charging). Although the math is
fairly tedious, the result is that the capacitor voltage can reach Pi/2
or 1.57 times the peak of the applied sinusoidal voltage for the
lossless case. This means the output can reach up to 2.22 times the RMS
faceplate voltage (or 33 kV) for the lossless case. While Ohmic losses
will reduce this a bit, this implies that a 15 kV transformer might
stress the tank cap to over 30 kV. Upon oscillatory discharge, the
dielectric will be stresses to 2X this value, or about 60 kV. This is
another way of looking at why the tank cap's DC rating should be at
least 3-4X the expected applied RMS voltage. And it can get worse... if
the gap missfires and we catch the NEXT peak, the voltage could be Pi
times the peak of the input sinusoidal voltage (approaching 66 kV!).
Practically speaking, I believe this voltage multiplication effect
occurs in my resonant charging system, since I'm running with 18 gaps
(0.54") off a pair of 15-60's, and at full power the system is actually
firing at between 3-4X per half cycle (albeit somewhat chaotically).
-- Bert --