RE: Gap Question

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

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

Bart:
I thought about what you said with the negative resistance thing.
May I lay something out that does not use real values but values
arbitrarily picked out to make the example simple.  I may be way off
base but would like some in put.  I think the idea has merit.

I was thinking it may appear to be negative resistance but may not
really be.  Maybe it is like having a gap that has different dimensions
when it heats up.

Let me try to explain.  And before anyone starts quoting some actual
values try to look past that for about 30 seconds just to get the idea I
am getting at.  Then fire away with all the real value stuff.

Let's pretend for the example that:
1:	The breakdown voltage of air is 100 volts per inch. And
2:	That an arc has a certain amount of resistance per length.
	But that resistance follows a logarithmic curve or spiral.
	What I mean by this is like that of a logarithmic spiral.
	Where the curvature gets tighter and tighter as the spiral
	Curves inward.
	Now draw a line from the center outward.  Measure the distance
	from center to where the line intersects each turn of the
spiral.
	So say 0.5=3, 1=6, 1.5=12, 2=24, 2.5=48, 3=96, 3.5=192 etc.
	

Imagine only the spark gap the primary coil and the capacitor.
And all this is at the time of break down for the gap.

Ok say we have a gap of 3" that would give 300 volts for break down and
 >From the curve above the resistance of that arc would be 96 ohms.
Using plain old ohms law you would get a current of 3.125 amps.

Now let's say the electrodes get hot.  Instead of just looking at it
like
The voltage breakdown got lower, lets assume it acted as though it made
the
distance between the electrodes closer, which would have a lower
breakdown voltage.  I think of it like the hot air/ions whatever might
act as an
extension of the electrodes making them have a larger diameter and
therefore
be closer together.

So lets say that the heat involved made the gap ACT as though the
distance was 2.5" even though the measured distance might actually be
3".

This would give a break down voltage of 250 volts and a resistance of 48
ohms.  So the current would be 5.2 amps.  So the voltage the cap charged
to was 50 volts lower but the current went up.  Not because of negative
res.
but because the electrodes in a way are now closer.

So is it that the gap has a negative resistance?
Or is it that the heat makes the gap act as though it has,
different dimensions (a closer spacing)?
so the gap acts different?

I know this might be reaching a little but I think there is some logic
in it I would like some opinions on.

If what I am saying had some truth to it then if one did not take into
account the gap acted as if the distance were closer it would seem that
there was indeed negative resistance.

Any thoughts?  And keep in mind I am no math whiz.  Just laying out a
concept and hoping to get some qualified people thinking / talking so I
can hear bout it.

Thanx

Luke Galyan
Bluu-at-cox-dot-net
http://members.cox-dot-net/bluu

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Sunday, February 22, 2004 3:45 PM
To: tesla-at-pupman-dot-com
Subject: Re: Gap Question

Original poster: Bart Anderson <classi6-at-classictesla-dot-com>

Hi Luke,

Yes, I'd agree fully with Gary. But, opinions are either how someone has

reasoned the logic or their experience, so opinions will vary, but they
are
needed. The second part of that is how you interpret the info and what
you
choose to do with it.

With that said, my opinion: the only way I see gap losses changing
between
gap types for a given breakdown V is heat dissipation and stabilization
of
breakdown V over consecutive bangs. It should be obvious that electrode
temperature affects breakdown V. If parallel pipes have good heat
dissipation characteristics, then that would aid stabilization of the
breakdown V. In that respect, they would tend to have lower losses in
comparison to some other type of gap which cannot dissipate the heat as
well. However, the term "losses" as described here isn't as though you
can
just add more power to the assembly to make up for the lower breakdown
V.
You would have to cool the electrodes to bring the breakdown V back to
equivalency.

The gap has a negative resistance characteristic, in that when the
breakdown occurs, there is a current across the gap and an associated
voltage drop across the gap. The voltage across the gap will increase if

the current decreases. Note this is just the opposite of what you might
think in terms of voltage and current. Now, with that in mind, if a gap
has
a lower resistance, and this resistance is negative, the current will
follow the resistance and decrease: higher breakdown V. So, does that
throw
a wrench into the works? I'm not the right person to really discuss this

situation (others know far more than I). That's about as much as I've
picked up on the situation.

Take care,
Bart

Tesla list wrote:

 >Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com>
 >Don't believe everything you read on the web, or this List.  Opinions
on
 >everything vary, and it's up to the reader to choose who they believe.
 >I would agree with your logic; I don't think you're missing anything.
 >
 >Gary Lau
 >MA, USA
 >
 >
 >Original poster: "Luke" <Bluu-at-cox-dot-net>
 >
 >It has been said that a gap using parallel pipes will be like having
 >smaller gaps in parallel and will lower the gaps resistance / loses.
 >
 >This does not make sense to me.  Maybe someone can enlighten me.
 >
 >If what is meant is, lower resistance before the gap breaks down then
it
 >
 >would be similar to decreasing the spacing.  This would be like
reducing
 >
 >the spacing of the gap.  That would reduce breakdown voltage and be
 >undesirable.
 >
 >If what is meant is, lower resistance while the gap is arcing that
 >doesn't
 >make sense.  The gap only arcs at one place at any one time.  So how
 >would
 >that gap have less resistance if the arc area or distance has not
 >changed.
 >
 >Can any one show me what I am missing?
 >
 >Luke Galyan
 ><mailto:Bluu-at-cox-dot-net>Bluu-at-cox-dot-net
 >http://members.cox-dot-net/bluu
 >
 >
 >
 >