Re: Measuring self-capacitance directly (Re: flat secondary)

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

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Peter Lawrence wrote:
> what would happen for a center feed coil if ID/OD where about
> 0.2 to 0.3

I'll model Marc's coil with the inner 30% of turns removed, so that
ID/OD = 0.3.  Also, I'll add a helical primary 10cm beneath the
flat secondary, of radius equal to the secondary OD. 
Acmi description is

  secondary {         ; A flat secondary with a 30% hole
     radius1 0.254
     radius2 0.076
     height 0          
     turns 529 conductor 28 awg
  }  
  
  primary {           ; Helic primary aligned with secondary OD
     radius 0.254
     height1 -0.1
     height2 -0.2
     turns 10 conductor 8awg
  }  

generating

    SCNY.L| SCNY.R|    PRMY.L| PRMY.R|SCNY-PRMY.M|SCNY-PRMY.K
  91.20 mH| 118.53|  80.33 uH|   0.03|  696.15 uH|     0.2572

which resembles a normal TC with quite high coupling.  Now I'll run
this through the tssp model...we get, for the rim-fed secondary
response profiles

 http://www.abelian.demon.co.uk/tssp/tmp/plf1.f1.gif

and a comparison:

             Full Spiral    70% spiral
 
       Ldc:    93.1 mH        90.6 mH      
       Les:   129.6 mH       102.7 mH
   Les/Ldc:     1.39           1.13
Imax/Ibase:   200%           160%

The current max is reduced in the incomplete spiral, thus causing
the lower Les/Ldc ratio.  So those discarded inner-most turns may 
not be contributing much to Ldc, but their presence encourages 
internal capacitance to raise that current max and thus boost Les.
The same effect could no doubt be achieved by a non-inductive flat
central plate, or a central sphere or toroid.

      Fres:   161.5 kHz      151.6 kHz
       Zft:   131.5 Kohms     97.8 Kohms
  Q-Factor:   213            175

Next we'll choose a primary cap to tune the 80.33uH to 151.6kHz,
lets say 13.72nF.  And let's have a 10kV firing voltage.  Then the
time domain response of the dual resonator would be

 http://www.abelian.demon.co.uk/tssp/tmp/plf1.f1-td.gif

The two mode frequencies here, are 132.4 kHz and 172.7 kHz.
Despite the fairly high coupling coefficient, the voltage profile
seems very smooth, with little in the wave of higher modes. The peak
voltage gradient is 905 V/turn at around 13% position (in from the
rim). 
--
Paul Nicholson
--