Vacuum Gap

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

Original poster: "Jeremy Scott by way of Terry Fritz <teslalist-at-qwest-dot-net>" <supertux1-at-yahoo-dot-com>

So I've created my vacuum gap -- PVC electrical 'T'
junction and an old vacuum cleaner motor.

I've used 3/4" copper pipe with some very thick
copper screw fittings on the business ends. I figure
if the fittings get too corroded, I'll sand their
faces
down or buy new ones. :)

I've still got this notion in my head of creating a
digitally controlled spark gap. I'm still working on
the rotary gap, but for now I'm wondering if a static
air quenched vacuum gap would be a better candidate
for digital control.

The voltage and therefore the frequency of gap firing
is a function of the pressure and the distance between
the electrodes. The distance is fixed but the
effective pressure would be a function of how fast the
vacuum motor goes. (The one I've got is pretty
powerful -- I think it's from a huge shopvac)

I thought about affixing a phototransistor to the T
junction to sense when the big spark happens. That
phototransistor would turn the spark into a digital
pulse after buffering some of the noise out
with a few discreet electronic components.

The frequency and duration of that pulse could then be
counted by my Basic Stamp, which could then adjust the

speed of the vacuum motor.

So for example, suppose I adjusted the gap distance
too closely and the plasma-arc channel forms and
doesn't go away. (quench failure) The phototransistor
would inform the BS of a very long 'on' pulse. The BS
would decide that we need more quenching and step the
speed of the vacuum motor up until the spark goes
away. If there's a too long 'off' pulse, the BS would
lower the speed of the motor. So we bounce back and
forth between these inputs until the desired breakrate
is reached. This is assuming that the gap was set at a
'resonable' (if not exactly right) distance to begin
with.

If the BS steps the motor to it's highest speed and
there is still a quench failure, the BS could then
shut off coil power.

If there isn't a spark immediately after turning the
power on, then it'll step the motor down until there
is one, eventually shutting the coil down if no spark
when the motor is stopped.

Another sensor could be wired into the saftey gap,
which would help keep things under control by shutting
the coil down if arcs occured there too often.

The only issue I see with this setup is that there
might be some lag time between changing the motor
speed and when that actually affects the air pressure
in the gap enough to change the breakdown voltage.
If it's a long time, then bad things could happen.

What do you think?