RE: Static Gap question.

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi Gary,

On 12 Feb 2004, at 8:11, Tesla list wrote:

 > Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com>
 >
 > I have heard reports that increasing airflow through a gap beyond some
 > point leads to arc-stretching and diminished performance.  Personally
 > I've not seen this.  I would imagine that very high airflow would lead
 > to a higher breakdown voltage and possibly unstable performance.  With
 > my sucker gap I have a dimmer to the vacuum cleaner motor and have
 > seen only that performance is poor with no air, and performance
 > improves as airflow is increased to something like 20%, with no change
 > either way beyond that.  The motor is very loud and draws a lot of
 > power at full throttle, so I tend to run it only at the 20% level.
 >
 > Gary Lau
 > MA, USA

I once tried firing a *jet* of air through a single static gap at a
range of airflow speeds to see where the truth lay in all the stuff
that was said about quenching at the time (again, last century). The
question was: Could the gap be made to quench first notch with air
streamers or no streamers coming off the secondary (i.e. NOT attached
discharges which I already knew would effect quench by proxy). At the
extreme airflow, the gap discharge was blown into a 4"+loop by which
time first notch quench was taking place. Unfortunately, at least
half the available primary energy was now disappearing into the blown
loop and not the secondary as evidenced by the drop in secondary
output. The drop in secondary amplitude was also seen on the scope.

The airflow in question was a true high velocity jet, not a gentle
breeze from a muffin fan.

The conclusion reached was that under air or no streamer conditions,
first notch quench could be effected but was a complete waste of time
due to the consequent primary losses now occurring. Another bit of
pie-in-the-sky theory exposed to be wishful thinking.

At that point, I postulated that there were in fact two types of
quench that to date nobody had distinguished between. One was the
hopeful first notch quench as promoted by supposed authorities on the
subject and the other was a more placid prevention of power-arcing in
the gap (a quite attainable and useful aim). Of course, solid-state
gaps now do what air-gaps couldn't. I documented some expts I did
using a paralleled bank of power MOSFETS as the gap in a small coil
back around 1996 and took much interest in noting the effects of
quenching at zero voltage and current crossings. The "HT" supply for
that coil was a 30V regulated supply capable of about 1.5A output and
some polypropylene capacitors wired in parallel. One of the notable
features about the primary waveform was that it had a log rather than
lin decrement when running with pure resistance. A pulse generator
applied to the MOSFET gates enabled me to fine tune the dwell and
breakrate and I could run the coil right up to capacitive discharge
CW. Some details of these expts will no doubt be residing in the list
archives somewhere.

Malcolm

 > Original poster: "Luke" <Bluu-at-cox-dot-net>
 >
 > If forced air is used to help quench the gap, can you have too much
 > air flow and hurt performance?  If so any opinion as to what happens
 > that hurts the performance?
 >
 > Luke Galyan
 > Bluu-at-cox-dot-net
 >
 >
 >