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Re: Toroid size

In a message dated 9/11/00 11:35:20 AM Pacific Daylight Time, 
tesla-at-pupman-dot-com writes:

>  Original poster: "Kennan C Herrick" <kcha1-at-juno-dot-com> 
>  Are there experienced people here on the "List" who can advise as to the
>  appropriate size of a >smooth< toroid vs. the length of spark at
>  "breakout"?
>  On the basis of my current experience, using a 4" c.s.d. x 20" o.d.
>  corrugated toroid, I find that that yields ~24" sparks with my present
>  set-up.  I'm ultimately anticipating trebling my primary current (as I've
>  mentioned before in prior postings), so as to up the secondary voltage
>  proportionally, and I need to get a feel for a) the improvement in
>  breakout capability that I might expect using a smooth vs a corrugated
>  toroid and b) whether, for an anticipated spark length of 4-5 feet, a 4"
>  c.s.d or a 6" c.s.d. would be more appropriate, atop a 12" dia secondary.
>  It would seem that, if too-big a c.s.d. is used, spark "breakout" might
>  not occur.  That would necessitate the use of an auxiliary electrode of
>  lesser radius for producing the spark--and thus the "dancing around" of
>  the spark, that has been mentioned and that we all favor, I am sure,
>  would be precluded.
>  Any comments would be appreciated.
>  Ken Herrick


You are correct that a radius that is too large will prevent
breakout.  Whether or not breakout occurs or not will also 
depend on the tuning of the coil.  If the primary is tapped
"inward", this lets the breakout occur more easily, but tends
to give shorter streamers.  I use a 4" by 13" smooth toroid
for 42" streamers at 600 watts, but the streamers can break
out at a lower power and voltage.  For instance 24" sparks
can easily break out also, depending on how the tuning is
adjusted.  I like to make the minor radius about 1/10th the
expected spark length.  The sparks can go farther than this,
but seem to take a disproportionate amount of power.

When I use a corregated toroid, I have to use a 4" by 17" or
even a 5" by 20" to get the same 42" lengths, but I am
still plagued by multiple breakouts which tend to rob the
spark of length.  I consider a 4" by 13" smooth toroid to be
more effective than a 5" by 20" corregated one.

A 4" by 13" is barely large enough for a 4 foot spark (at 120 bps),
but at higher bps it is probably fine.  Also a smaller toroid can
be placed below the main toroid to help increase the spark length.

A 5" by 20" smooth toroid works well for 70" sparks I am told.

I don't like to use anything as large as 6" by 26" corregated for a
small coil that uses only 600 to 800 watts and gives up to 49"
sparks although it does work.  The 6" by 26" corregated unit 
hit's it "zone" when the sparks reach 57" to 67" + as a minimum.
Of course the smooth toroid of this size can give much longer
sparks, up to 10 feet long I believe.

Of course the breakout will be influenced by the bang size also,
and a high bps coil may have trouble breaking out at the same
power input as a low bps (large bang) TC.  So all my comments
here are necessarily of a general nature.

John Freau