Re: Racing Spark Prediction

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FutureT@xxxxxxx 

In a message dated 5/21/06 3:12:38 PM Eastern Daylight Time, 
tesla@xxxxxxxxxx writes:


> > I would think that the peak capacitor voltage would be lower in this
> > (over-heated gap) mode.
>
> another post about the racing sparks at lower than normal voltage:
>
> http://www.pupman.com/listarchives/1998/July/msg00132.html
>
> and your explanation of this:
>
> http://www.pupman.com/listarchives/1998/July/msg00163.html
>
> i`m starting to think, that racing has something to do with the first
> notch quenching, probably not exclusively with a fact of quenching
> itself, but also with set of conditions that assist in it - more
> distance between pri & sec, good streamers loading, e.t.c.
> and of coz the fact that secondary after quench may ring freely on
> it`s own natural freq only is helping too.
>
> do you remember any racing on first notch in your coils?
> can it be such way, that most of D.C.`s coils quench after first
> energy transfer, because of relatively low coupling?


Deema  ( I understand this is a nickname for your name),

Yes, I liked my own explanation that you refered me to.  On many
coils when the quenching fails for whatever reason, the output
sparks get weaker but no racing sparks occur.  On
some coils, racing sparks result.  Maybe it depends on how
close the coil is to being on the verge of producing racing sparks
in normal operation.  Most of my coils quenched on the 2nd or
3rd notch.  I had to use special methods to obtain 1st notch
quenching.  It seems that larger coils have an easier time
obtaining 1st notch quenching.  I never had a large enough area
to run large coils.  At one of Ed Wingate's Teslathons, Bert H
scoped Ed's magnifier and found that it quenched on the first
notch at full power, as the power was decreased the quenching
moved to the 3rd or 4th notch due to decreased streamer loading.

In the example of my coil which gave many racing sparks when
the gap overheated, I unfortunately don't remember if my streamers
shortened and if so by how much.  If the streamers didn't shorten,
then it can't be the decreased spark loading that contributed to
the racing sparks.  Certainly the quenching would have been
very poor though with such hot gaps.  But the question is how
poor?  Did it quench on the 6th notch, the 10th notch, etc.
It seems to me there wouldn't be much energy left by then.
Usually by the 3rd or 4th notch there's not much energy left
in the system.  Is there enough energy left to create racing sparks?
As the energy swaps back and forth, various new
frequencies (sidebands) are produced, but
do they carry the needed energy and voltage to create racing sparks?
Or is there something else we are missing.

Yes, D.C's coils might quench on the 1st notch due to relatively
low coupling,  But in general a coil can quench on the 3rd or
4th notch and still not show racing sparks.  The onset of racing
sparks is sudden once the coupling is tightened too much.  For
example on my TT-42 coil, simply removing 1/2" of winding at
the bottom of the secondary cured the racing sparks.  Originally
it was plagued by racing sparks which actually destroyed some
turns near the bottom of the secondary winding.  Later I installed
a much larger toroid onto the TT-42 coil as a test.  This prevented
streamer breakout completely at times, but no racing sparks
appeared.  So even without breakout at full power, no racing
sparks appeared.  Perhaps the larger toroid improved the
linearity of the voltage along the secondary and prevented
racing sparks by that mechanism.  Recently I was demonstrating
the TT-42 to a visitor, and I saw racing sparks.  The normal
toroid was installed, not the much larger one.  My guess is
that the house ac line voltage was higher because it was wintertime.
In the summer they reduce the voltage some because the
power distribution system can't handle the peak loads with
air conditioning, etc.  Or maybe the coil is getting more
powerful with age (sort of like an aged cheese).  Or maybe
the insulation is getting weak (sort of like a rotting cheese).

To continue (yes this post is getting long in the tooth)...
It is commonly accepted that better quenching permits tighter
coupling.  That is the theory.  If the energy doesn't actually
swap back and forth, it doesn't get the chance to create
multiple side frequencies which then create voltage ripples
along the secondary.  I once made a tube coil which had
such strong voltage nodes along the secondary that I could
move a fluorecent tube along the secondary from bottom
to top, and it would light, go dark, light again, go dark, etc,
and clearly show where the modes are.  Although a spark
gap coil runs in disruptive mode (contrasted with continuous
mode for the tube coil), still the disruptive coil's behavior
may become more continuous-like in the sense of the
continued energy swaps, and continued interactions of
the primary and secondary causing the sideband frequencies
which may lead to the racing sparks.  It would be interesting
if someone who has the ability could calculate the energy
and voltages that might appear under such conditions and
see if they are indeed great enough to form racing sparks.

One time I built a coil and ran it with a rotary gap.  There
were no racing sparks.  Then I removed the rotary and installed
a static gap.  Now there were racing sparks everywhere on
the secondary.  I had to raise the secondary by 3 inches to
stop the racing sparks.  The streamers were the same
length in either case.  The static gap had a few sections
making it a series static gap.  I have no idea how well
it might have quenched compared to the rotary.  I didn't
measure the bang sizes so I can't comment on that either.
I remember Harry Goldman mentioning in TCBA News that
coils using rotaries usually tolerate a considerably tighter
coupling than coils using static gaps.  Yet I remember
Terry saying that his static gaps quenched very well,
and that rotaries don't quench at all.  So I wonder if Terry's
coils with rotaries can tolerate a tighter coupling than
his coils with static gaps?  Maybe Terry has done this
test?

I remember the heydays a few years ago when many folks
were doing many tests.  These days I don't see many
such tests except for solid state coils.  Of course the
solid state work is very interesting and very good.

John