Re: SRSG gap distance?

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

Original poster: FutureT-at-aol-dot-com 

In a message dated 1/16/04 8:50:57 PM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:

>And if this is all true how do you determine how close the gap should be on
>a SRSG?
>Is there a formula for this?  Or is it just set really small and the
>distance doesn't really mater?
>
>Luke Galyan


As you may have guessed by now, there are a number of factors
that effect this, but basically the gaps are set very close.  If the
gaps are set too wide, gap firing will be erratic.  This is because
the swirling air in the electrode vicinity makes it more difficult for
the spark to jump a given distance at a given voltage.  If the gaps are
too narrow, and if the gap electrodes are thick in diameter, the mechanical
dwell time may be too long, and this may permit "re-firing" of the
gap while they are still aligned from a previous firing.  This leads
to poor operation and causes the coil to draw heavy current.
Re-firing mostly occurs with small rotor diameters turning at slow
speeds with small capacitor values which may let the caps
recharge to the firing voltage within the dwell time.  This tends
*not* to occur at 120 bps due to the larger (LTR) value caps
usually used.  Generally this refiring is not a problem, but I
mentioned it since it can occur.
Many of these issues are discussed in the list archives.  I hope
you are spending some time reading the old postings.  However
be forewarned that much incorrect information exists.  There
are also a *great* number of erroneous comments at various websites.
I realize it's difficult for a newbie to separate the wheat from the chaff.
But there are more issues.  If the
transformer voltage is very high, then the gaps can be spaced
further apart, since a higher voltage can jump a wider gap.
Generally small coils use a closer rotary gap setting than
larger coils.  Some coils may use more resonant charging than
others, so a wider gap may be tolerated due to the higher
available voltage.  Very thin electrodes may require closer gap
settings due to the shorter dwell time.  Normally these kinds of
parameters of Tesla
coils are not calculated using formulas, rather they are based
on experience and on trial and error.  Part of the process of
building a Tesla coil is this *tweaking* which must be done
to optimize the coil's operation after it's built.  As Gary mentioned
in his posting, so many factors interact that it becomes difficult
to calculate certain things, especially with the present degree
of TC knowledge and available data.  Folks who have built a
number of coils soon develop a sense of what works and what
doesn't, and how things must be adjusted.  I could tell you
many stories about folks optimizing their coils, etc.  It's great
that you want to gain a somewhat complete understanding
of coils before beginning to build.  Such a dedication to coil
understanding is to be commended.  However when you do build
one, a new level of understanding based on experience will be
gained.  Many of the questions that you ask are so basic that
experienced coilers sometimes forget that a new coiler has no
basis for *seeing* the obvious aspects of what is mentioned.
Most aspects of Tesla coils are pretty well understood
these days.  Be assured that there are many other types of
engineering challenges (other than Tesla coils) which also
use a large dose of empirical data and trial and error in the
design process.  One of the things that makes Tesla coiling
such a fantastic hobby is the wide range of knowledge,
understanding, theory, practical experience, controversy,
and research opportunity, that is needed/offered.

John