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Re: Vacuum Gap



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

Sounds like your setup is similar to mine --
I have a 7" coil, 1.5 - 3KVA PT. I'm not sure
what the vacuum cleaner motor is rated at, but
when it's on full blast it consumes about
3 amps -at- 120V (360W ? )

My tank cap is about 10nf / 100kV worth of
commercial pulse caps, I'm pretty sure the
PT will have no problem charging it more
than once on every AC half cycle, so I'm
going to target 120BPS as my initial break
rate, then make adjustments to get to 240.

I've got an electrical PVC t junction box,
The only way for air to get in is through
the ends of the copper pipe electrodes.
I may be putting a hole on the top so that
air can travel past the top parts of the
electrodes, not just the bottoms. I'll
run a 'smoke' test like they do in windtunnels :)
I haven't tried this gap with PT power yet,
but it  works okay on my small NST coil.

I might put some thoriated tungsten rods
on the bottoms of the pipes to make the
preferred arc location at the bottom where
all the suction is.




--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: "bob by way of Terry Fritz
 > <teslalist-at-qwest-dot-net>" <yubba-at-clara-dot-net>
 >
 > hi Jeremy,
 >   I would get  in the ballpark first by  running
 > your vacuum cleaner motor
 > though a variac and  looking for the longest spark.
 > This will also tell you
 > how close the coil is to  being in tune. On my 8''
 > coil  the  motor speed
 > of the vacuum cleaner  motor changes the spark
 > length in a bout 2 or 3
 > seconds.  I am using a 1 kw motor with slots cut in
 > the  PVC pipe to allow
 > air  to go  right into the  gaps. I have the end of
 > the gap sealed so al
 > the air has to go though the  gaps. With 3 kw
 > driving the coil i  usually
 > need about 3/4 power to the motor for best results.
 >
 > bob golding
 >
 >   At 07:41 03/08/2003 -0600, you wrote:
 >
 > >Original poster: "Jeremy Scott by way of Terry
 > Fritz
 > ><teslalist-at-qwest-dot-net>" <supertux1-at-yahoo-dot-com>
 > >
 > >Yeah the BPS would be dialed in -- the BS2p40
 > >microcontroller has a command which can measure
 > >the width of a pulse (PULSIN) -- This would
 > >let me measure gap conduction time and could
 > >probably let me measure the relative
 > >resistances/reactances of various tank
 > configurations.
 > >According to the manual, the BS2 can measure pulses
 > >with .75 microsecond resolution to 49 milliseconds.
 > >(Stores the result in a word, 65535 possible
 > values)
 > >
 > >There is also the COUNT function which will count
 > >the number of pulses that occur in a range of
 > >287us to 18s. Minimum pulse width is 1.20
 > >microseconds.
 > >It can measure frequencies (square wave) up to
 > 416Khz,
 > >so I think accurate feedback for a 120BPS gap is
 > >possible. I probably wouldn't set the sampling rate
 > >at one second, maybe like two AC cycles (33ms or
 > so).
 > >
 > >This assumes of course that I properly sheild
 > >everything and run the digital circuitry off
 > >batteries etc..
 > >
 > >I was thinking of using a regular LED as a
 > photodiode,
 > >or using an IR phototransistor as I can't seem to
 > >locate any visible light ones right now. (Spark
 > gaps
 > >emit some IR light right?) My PVC T junction will
 > be
 > >mostly dark inside when there is no spark. Maybe a
 > >little ambient light from the glowing copper
 > >electrodes. :) I'll probably use a lens or at the
 > very
 > >least some black plastic 1/4" hollow tubing to keep
 > >the sensor far away from the gap, but close enough
 > to
 > >detect a break.
 > >
 > >
 > >
 > >--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > > > Original poster: "Gerry Reynolds by way of Terry
 > > > Fritz <teslalist-at-qwest-dot-net>"
 > > > <gerryreynolds-at-earthlink-dot-net>
 > > >
 > > > This has a feel to it of open loop since the
 > > > controller doesn't have a
 > > > target to shoot for like BPS.  I wonder if a
 > counter
 > > > could be fashioned to
 > > > allow you to "dial in the BPS" or if spark
 > duration
 > > > is what you want to
 > > > control, then be able to dial in the spark time
 > (as
 > > > in pulse width).  A
 > > > pulse width comparator might be helpful for the
 > > > latter.  Closed loop
 > > > response would need to be set to account for the
 > > > response of the vacuum
 > > > system.  Instead of an optical sensor by the
 > spark,
 > > > you might want to pipe
 > > > the spark light to the controller so everything
 > > > could be shielded.
 > > >
 > > > Interesting concept.  have no idea how this
 > would
 > > > compare in performance to
 > > > a SRSG.
 > > >
 > > > Gerry R
 > > > Ft Collins, CO
 > > >
 > > > ----- Original Message -----
 > > > From: "Tesla list" <tesla-at-pupman-dot-com>
 > > > To: <tesla-at-pupman-dot-com>
 > > > Sent: Thursday, July 31, 2003 8:26 PM
 > > > Subject: Vacuum Gap
 > > >
 > > >
 > > >  > 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
 >
=== message truncated ===


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