Re: xformer/cap - match

To: tesla-at-PUPMAN-dot-com
Subject: Re: xformer/cap - match
From: Hollmike-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Sat, 23 Oct 1999 10:44:05 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

In a message dated 10/23/1999 5:48:40 AM Mountain Daylight Time, 
tesla-at-pupman-dot-com writes:

<snip>
> 
>  Are these assumptions correct? Any comments are welcome!
>  
>  Safe coiling to you!
>  
>  Herwig
>  
    It seems to me that Terry F. has been using a what he terms, a  
"Larger-Than-Resonance" capacitor with good success.  He can correct me if I 
am wrong, but I think he has been using a cap with a value about twice that 
of the calculated impedance match.  
    On the other hand, NST's (at least Allanson brand) are meant to be 
operated at a voltage of about 1/2 of the voltage shown on the nameplate.  
The 15kV is need to get the neon light started, but then the load of the tube 
is supposed to cause the RMS voltage to be 7500V during continuous operation 
for the transformer to last longer.   I read this on Allanson's web site - 
probably in their online catalog (but don't hold me to that). 
    So if one equates the two conditions above, it seems to me that really 
one should use a capacitor value of   0.5*maxV/I = 1/(2*pi*f*C)  or if this 
is rearranged, C = 1/(pi*f*V) where V is that nameplate voltage.  This would 
suggest that the primary capacitance should be twice what we have been using. 
 
    I do remember reading a note by Tesla that the primary cap should be able 
to take ALL of the energy provided by the transformer and it would seem that 
in the case of NST's, doubling of the capacitance we have been calculating 
would certainly do that.  It would also be simple to adjust the spark gap to 
fire at one half voltage by simply adjusting it to fire when the variac is at 
50%.  It would save a lot of NSTs from early death too. 
      This would not be the case for pole pigs, MOT's or other transformers 
that are not current limited.  The caps for these should be designed in the 
normal manner - based on the power they are designed to be used at.
    I would like to hear comments on this as I haven't heard of anyone 
mentioning this before.  It is just a thought that recently occured to me and 
since Herwig brought up the subject, I figured I would present this idea.
Mike