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Re: TC Output Voltage
Tesla List wrote:
>
> >From lod-at-pacbell-dot-netMon Nov 11 23:18:12 1996
> Date: Sat, 11 Nov 1995 21:37:05 +0000
> From: GE Leyh <lod-at-pacbell-dot-net>
> To: tesla-at-pupman-dot-com
> Subject: Re: TC Output Voltage
>
> Malcolm Watts wrote:
>
> > Point taken :) I think effective arc resistances can only be measured
> > for and be singly applicable to a well defined set of conditions for
> > a particular system. I remember doing a rough estimate on one running
> > coil of several kilohms. Channel current and channel length are both
> > rather variable quantities. A low Zo is going to give a rather low
> > unloaded Zshunt which equates with low voltage production for a given
> > Zbase IMO. (Zo^2 = Zbase x Ztop)
> >
> > Malcolm
>
> How did you estimate Zarc? Do you think that it can be determined by
> watching the decrement of the current waveform at the base of the
> secondary coil?
> If I remember correctly, a resonant tank ckt is critically damped
> when SQRT(L/C) = 2R, and max power xfer occurs at SQRT(L/C) = R.
> TC secondaries seem to ring for quite a few cycles, indicating that
> the typical Zsec is actually much _lower_ than Zarc. If this is the
> case, how does adding a toroid help with spark production?
>
> -GL
Greg and Malcolm,
For a given coil setup, it should be possible to measure the secondary Q
by doing cycle counting on the output waveform via a pickup plate while
the coil is producing heacy streamers. Admittedly, this is kind of tough
to do, as the arc characteristics are constantly changing. I've had
limited success by taking a number of successive measurements on my 10"
coil by using a storage scope and trying to estimate the "average".
My primary Q with gap firing is about 11, and secondary Q runs at about
19 (single shot, breakout case), declinings with increasing power levels
to around 11-12 under full power with streamers. The streamers will
appear as "leakage current" across the secondary cap - as Greg suggests,
this seems to imply a fairly high "average" arc impedance (about 460K
Ohms) versus secondary surge impedance Zo (about 42000 Ohms) even at
full "cook". However, I have little doubt that the peak streamer
currents are significantly higher, and that below a certain voltage
value the current drops sharply as the streamers can no longer be
maintained. BTW, the top toroid has about 26pF of effective capacitance,
and I've got about 15 pf of secondary self-C, and Fo is about 91 kHz.
I'd take more meaurements under high-power, but I'm concerned about
"frying" my scope - I get "zapped" from near-field effects just touching
the scope to make adjustments. Maybe a chicken-wire screen to block the
electrostatic field betwwen the coil (and me) and the scope??
Safe coilin' to ya!
-- Bert --