Re: Topload and Arcing

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

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

In a message dated 8/13/01 10:35:38 PM Eastern Daylight Time, 
tesla-at-pupman-dot-com writes:

> I've seen on the web have two toroids, 
>  and I recall reading somewhere on the list that this configuration can 
>  prevent (or alleviate) arcing to the primary. Is this correct? If so, how 
>  does this work? Is this primarily why the stacked toroids are used?
>  Finally, how do I calculate the total capacitance of the stacked toroids? 
>  Do I treat them as two separate toroids, calculating their free-space 
>  capacitance (from the equation) and summing them as two parallel 
capacitors?
>  
>  Thanks,
>  Danny

Danny,

If you coil is 30" tall, and the sparks are 40" long, they won't
have much of a tendency to arc down and strike the primary,
no matter what toroid you use.  The double toroid idea is
needed when the secondary is rather short.  For example on
my TT-42 TC, the secondary is only 19" long, and the sparks
are 42" long.  Without the small toroid under the main toroid,
(which raises the main toroid), the arcs do hit the primary at
times.  The small toroid raises the main toroid a little, so
the arcs don't hit the primary.  I could have simply made
the secondary 2" taller, and the sparks would not strike the
primary.  Since your planned secondary is much taller than
19", you shouldn't have any problem.  If only a small toroid
is added such as I did, it hardly changes the toroid capacitance
much.  But larger toroids will have more effect.  The capacitance
will not double with 2 identical stacked toroids, but will be maybe
50% larger than 1 toroid.  I think Bart or someone on the list
has some formulas or programs that will calc this.  Maybe
Bart's JavaTC program does that calc.  Stacked toroids can
be used for two purposes; to raise the main toroid, or to 
increase the total toroid capacitance.

  My TT-42 coil can be seen at:
    http://hometown.aol-dot-com/futuret/page3.html

John Freau