Re: sec input impedance

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gary Johnson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <gjohnson-at-ksu.edu>

Jan:
The input impedance of the dozen or so coils that I have tested have been in
the range of 25 to 100 ohms. If you design your driver for 50 ohms, you
should be in the ball park.  Input impedance is a function of the coil
height to diameter ratio, the wire thickness to wire spacing ratio, and the
skin effect, which in turn is a function of the wire thickness and
frequency. I have been working on some simple empirical equations for input
impedance for some time, and hope to have them available in the next few
months.
   When the discharge occurs, the input changes from constant impedance to
constant current.  That is, the current remains constant as the input
voltage increases.  At a minimum input voltage that is adequate to produce a
discharge, the impedance may change from 50 to 200 ohms when the discharge
occurs. Crank up the variac to double the voltage, the input current stays
the same, so the impedance has gone to 400 ohms.

Gary Johnson
At 04:41 PM 07/30/2001 -0600, you wrote:
>Original poster: "Jan Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jwagner-at-cc.hut.fi>
>
>Hi,
>
>after quite some pause, I finally got around to carry on with my solid
>state TC project. 
>
>My question now: how do you calculate the TC secondary input/base
>impedance, for an unloaded seconday coil? Ok measuring some arbitary
>coils might be easy, but I'd like to get the height&diameter&turns
>values so I could make a coil of driver matching impedance, without
>trial and error.
>
>To get the simplest estimate of the input impedance, is it just the AC
>resistance of the coil? 
>
>I've some tables with AWG# vs. AC/DC resistance ratios. My thinking is
>that 1) calculate dimensions for wanted f_res with given wire AWG#, 2)
>calculate DC resistance from total wire length, 3) calculate AC
>resistance with help of table. Ok the table is valid only for straigt
>conductors, but any ideas if the calculated value is still "in range"
>(+-10%?) of actual AC resistance? Anyone done this before or know if
>this is totally wrong?
>
>many thanks!
>
> - Jan
>
>
>