Re: Spark Gap Behavior (fwd)

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---------- Forwarded message ----------
Date: Sat, 28 Oct 2006 22:41:55 -0600
From: S&JY <youngsters@xxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Spark Gap Behavior (fwd)

Greg,

Regarding Bert's reference to negative resistance of the arc, search the web
for "Poulsen Arc Transmitter".  Before vacuum tubes came into widespread
use, a powerful DC arc from a carbon electrode to a water cooled metal
electrode in a hydrogen atmosphere and in a very strong magnetic field was
used for low frequency radio transmitters (power oscillators), made possible
by the negative resistance characteristic of the arc.  The really big ones
could generate 10s to 100s of KW.  As you can imagine, they were very
inefficient, and one had to be careful with the hydrogen filled chamber to
avoid an explosion.  A few years ago, an adventuresome experimenter built
one to drive a small Tesla Coil.  Very interesting reading, but I know of no
modern application.
--Steve
> > ---------- Forwarded message ----------
> > Date: Sat, 28 Oct 2006 10:46:59 -0700 (PDT)
> > From: G Hunter <dogbrain_39560@xxxxxxxxx>
> > To: tesla@xxxxxxxxxx
> > Subject: Spark Gap Behavior
> >
> > Does anyone know offhand how a TC single static air
> > gap behaves when conducting? Does it exhibit a fixed
> > voltage drop? A fixed resistance? A dynamic voltage
> > drop or resistance? Positive or negative
> > characteristic? If anyone has the data handy or if you
> > can point me at a link, please do.
> >
> > Thx,
> >
> > Greg
> >
> >
> >
> >
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>
> Hi Greg,
>
> A short, unconstrained (free burning) spark gap in air has a dynamic,
> negative resistance characteristic. As you increase current, the
> effective resistance drops such that the overall voltage drop across the
> gap remains relatively constant. For gap currents of 10 amps or more in
> TC tank circuits, a first cut approximation for a single gap's "on"
> behavior is a pair of back-to-back Zeners in series, each with a "Zener
> voltage" of between ~150-200 volts. The actual voltage drop for a given
> gap will be a function of electrode material(s), spark length, and (to a
> lesser degree) the peak current flowing through the gap. At very high
> currents, the resistance characteristic becomes slightly positive.
>
> Here's a link you may find useful - although it discusses triggered
> gaps, much of the information is applicable to simple 2-terminal gaps.
> http://www.reb3.com/pdf/sg_appl.pdf
>
> Bert
> -- 
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