Re: Spherical vs. toroidal top loads on tube coils

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Mddeming-at-aol-dot-com>

In a message dated 10/2/01 10:47:47 AM Eastern Daylight Time, tesla-at-pupman-dot-com
writes: 



>
> I don't happen to have a small toroid at the moment, but recently ran 
> across a fine spun 
> aluminum sphere about 7" in diameter.  Does anyone have any idea how a 
> spherical topload would 
> compare to a toroidal topload of the same general size?  Is there any 
> reasonable chance of it 
> working? 
>
> Thanks -- I'll look forward to hearing any ideas about this. 
>
> Dave 
>
>


Hi Dave! 
        If I remember correctly, and there are no typos, 
  The capacitance of an isolated sphere in picofarads is approximately 
         Cs=d/0.707 
where d is diameter in inches. 
The capacitance of an isolated toroid in picofarads is approximately 
        Ct=(1+(0.2781-d1/d2)) x 2.8 x sqrt[pi(d1-d2)(d2)/4] 
where d1 is Max diameter of toroid and d2 is diameter of the cross section,
both in inches. Just be sure that d1>2 x d2 or the inside diameter will be
negative and therefore not physically possible. 
        While you can't get a perfectly isolated terminal, the Ratio (Cs/Ct)
should allow you to work out a pretty good equivalence. 
Matt D.