Re: sec input impedance

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

HI Jan,
        The easiest way to determine Zbase for your coil is to 
measure it. The result will depend on the coil's proximity to its 
surroundings among other things.  For a discussion of the finer 
points, I recommend you read literature available at:

 http://www.abelian.demon.co.uk/tssp/


On 30 Jul 01, at 16:41, Tesla list 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.

Yes, but what happens when the sparks start flying? Remember, for a 
1/4 wave transformer, Zo = SQRT(Zbase * Ztop).  When a discharge 
occurs, Ztop drops to a degree which depends on the discharge current 
and output voltage under loaded conditions and as a result, Zbase 
rises considerably. You might think of the values swinging about Zo^2.
     Others building solid state drivers have found out about this 
phenomenon (to their cost on occasions). 
 
> To get the simplest estimate of the input impedance, is it just the AC
> resistance of the coil? 

No.
 
> 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?

The AC resistance of the coil is a dissipative value. An ideal 
transformer dissipates no power. Therefore, you are interested in the 
transformation ratio when looking for a matching impedance. 

Regards,
Malcolm