RE: Static Gap question.

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

Original poster: "Luke" <Bluu-at-cox-dot-net> 

Thanx for the input.
You say do not get too hung up on the small increments of adjustment for
a static gap.  Obviously there has to be some point to consider
starting.  For instance if a the approx gap desired is .3" then I could
just make it 3 gaps in series at 0.1" each.  That would be large
increments compared to what seems to be the norm.

So in your opinion at what would be a good increment to consider using?
Before I get the "depends on power rating etc." lets set up an example.

Say for a coil using a 15KV 60ma NST and a cap of say .02 mfd.
Yes I know that is not the LTR size, just picked a number and threw it
out there so we had a starting point for the example.

I am playing with design ideas and an opinion from someone with more
experience will help at least point me in a direction for an increamet
amount.

Thanx.

Luke Galyan
Bluu-at-cox-dot-net

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, February 12, 2004 7:11 AM
To: tesla-at-pupman-dot-com
Subject: RE: Static Gap question.

Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com>

I know of no mechanism or previous reference to a gap's on-resistance
being
related to its area.  I think the benefits to a large area are:
1) electrode erosion is minimized if it occurs over a large area
2) localized heating at the point of discharge is minimized if it occurs

over a large area
3) ionized air is more easily blown away if the discharge area is large,

leading to a more consistent breakdown voltage

Remember that the cross sectional area of the gap arc (arc resistance)
is
determined by the gap current, not the electrode geometry.  When you
have a
gap between two cylinders, it only occurs at one point (more or less) at

any given instant.  Why it doesn't tend to favor the ends with sharper
features or linger at some arbitrary site where ionized gasses and
temperatures are more favorable to breakdown is a mystery to me.

  >From another of your (Luke) posts, you ask about the consequences of
rather small gap distance adjustments.  Don't get hung up on this.
Static
gap breakdown voltage is not as predictable as any Tesla design
programs,
tables, or formulas may lead you to believe.  None of these predictors
takes into account the very recent history of the gap - i.e. how
recently
it has fired, which affects air temperature and ionization levels.  Look
at
this actual scope waveform taken on a static gap:
http://www.laushaus-dot-com/tesla/measured_waveforms.htm.  Notice how much
variation, both time and voltage,  there is from bang to bang (the rapid

vertical traces).

It is imperative to understand and believe that a static gap will never
(except for 5 seconds on the 5th Sunday of each month) fire at the peak
voltage of each mains half-cycle 120 times per second.

Gary Lau
MA, USA

.

Original poster: robert & june heidlebaugh <rheidlebaugh-at-desertgate-dot-com>


Luke: Yes the large area has two advantages; The total resistance of a
large
area gap greatly reduces gap resistance. When mounted vertical the gap
is
self cooling. When the small space of the series gap fires the total gap
spacing drops to minimum by the ion cloud conduction within the large
pipe
area dropping the total capacitor charge to a low voltage delivering a
large
ammount of total capacitor discharge power to the primary coil.  In
contrast
the safety gap dampens over voltage but dose not discharge the capacitor
charge acting like a voltage limitor not a spark gap. The same basic
service
but totaly different results.
               I use plate discharge spark gap discharge in my gas
lasers.
The
large space involved produces another action not noticed on small spark
gaps. That is a traveling wave action. I start  the discharge at one end
of
the laser and the arc travels the length of the tube with the light to
compound the intensity at the output end of the laser. THIS DELAY LINE
TRAVELING WAVE IS NOT SEEN ON TC SPARK GAPS, Because they are not 1
meter
long and the capacitors are not strip line capacitors.
       Robert   H
-- 


    > From: "Tesla list" <tesla-at-pupman-dot-com>
    > Date: Wed, 11 Feb 2004 08:03:37 -0700
    > To: tesla-at-pupman-dot-com
    > Subject: Static Gap question.
    > Resent-From: tesla-at-pupman-dot-com
    > Resent-Date: Wed, 11 Feb 2004 08:13:25 -0700
    >
    > Original poster: "Luke" <Bluu-at-cox-dot-net>
    >
    > I have looked around at the types of static gaps and have a couple
thoughts
    > of my own.
    > But let me see if I get this right.
    >
    > Assumptions.
    > The versions using the copper pipes in parallel to on another work
well
    > because they allow lots of surface area for the gap to cool thus
quenching
    > it rapidly?
    >
    > Gaps like the hyperbaric do not use the large surface area but the
good
    > quenching is assisted by the high volume of air?
    >
    >
    > Question 1.
    > If the gap is cooled off sufficiently and the gap is quenched well
say by
    > large amounts of air is there any other benefit to using a larger
surface
    > area for the spark gap?
    >
    > And question 2.
    > The JavaTC program estimation of the arc distance in relation to
potential
    > is based on the surfaces of the spark gap being curved like as in
large
    > dia. balls or pipes in parallel.
    > This assumes the distance between electrodes is not greater than
the
    > diameter of the electrodes.
    >
    > Would the same approximate distances be obtained for said voltage
if
flat
    > electrodes were used parallel to one another?  Say like two 1" dia.
discs
    > separated by ½".  Would that have a breakdown voltage close to the
    > breakdown voltage of two 1" dia. copper pipes in parallel to one
another?
    >
    >
    > Thanx
    >
    > Luke Galyan
    > Bluu-at-cox-dot-net
    >
    >
    >