RE: Gap Question

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

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

That put it into words that clicked with me.
Thanx.

And negative resistance characteristic is easier to swallow than
negative resistance.

Still mulling this over.

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: Tuesday, February 24, 2004 4:17 PM
To: tesla-at-pupman-dot-com
Subject: Re: Gap Question

Original poster: Bert Hickman <bert.hickman-at-aquila-dot-net>

Tesla list wrote:

 >Original poster: "Luke" <Bluu-at-cox-dot-net>
 >So if the current goes up the gap widens.
 >If the gap widens the resistance of the gap goes down.
 >If the resistance went down when the current went up
 >That is resistance not negative resistance.
 >
 >Luke Galyan
 >Bluu-at-cox-dot-net
 >http://members.cox-dot-net/bluu
<SNIP>

Hi Luke,

In a normal resistor, the voltage drop increases linearly as you
increase
current since the resistance is a constant (not a function of current),
so
that doubling the current simply doubles the voltage drop. This is
defined
as positive resistance characteristic.

The resistance of an unconfined arc will tend to decrease as you
increase
current since the conductive channel becomes fatter. The effective
resistance of the arc no longer a constant, but instead is a function of

the applied current. The voltage drop across an arc that bridges a fixed

gap length rapidly stabilizes to a comparatively low steady state
"burning
arc" voltage (~20 volts to ~150 volts depending on the electrode
materials).

As you indicate, the overall resistance of the arc is always positive.
However, an arc has a "negative resistance characteristic" since an
increase in current causes a rapid DECREASE in the arc's resistance such

that the arc's voltage drop tries to approach the burning arc voltage
for
the gap.

Macroscopically, a spark gap can be envisioned as a pair of back to back

Zener diodes with a 100-150 volt drop (Egap). Adding more gaps in series

will add more discrete voltage drops into the primary LC circuit. Each
additional spark gap adds an increment of loss (Iprimary*Egap), so
multiple
gaps will tend to be lossier than single gaps (all other things being
the
same). Multiple gaps often handle high power levels more effectively
without needing to resort to a heroic level of forced air cooling.
However,
a well designed high velocity single-gap system (such as Gary Lau's
vortex
vacuum gap) will be more efficient than a multi-gap system assuming that

they both style gaps are capable of quenching at the same primary
current
notch.

Best regards,

-- Bert --
-- 
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