Re: Air blast SG question

["Jason Johnson" <hvjjohnson13-at-xxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, November 17, 2000 8:34 AM
Subject: Re: Air blast SG question


> Original poster: Pyrotrons-at-aol-dot-com
>
> << Hi all,
>
> I like to know if some of you make test on air blast SG. I want to know
> if you had compare wide gap with small air flow vs narrow gap with high
air
> flow. What is your conclusions ? about quenching, general performance,
etc.
>
> Luc Benard >>
>
> Hi Luc and all...
>
> With a given gap spacing, increasing the velocity of the airflow will
cause
> the gap to break down at a higher voltage (as if widening the gap). The
> faster-moving air "blows away" the ions before they can create a path for
the
> discharge.
>
> I have stopped a 15kVRMS (20kV peak or so) transformer from arcing across
a
> 1/4" gap before.

How much airflow were you using? Alot I'd guess.

>
> I've found that quenching is great with a single static airblast gap, IF
and
> ONLY IF you have enough airflow.

This is similar to my experience. With my coil an airblast is the only way
to go. My MOTs eat all my other gaps for breakfast.

 Aron and I built and experimented with one
> once, and found the results to be similar to a RQ style multiple static
gap.
> However, I will say that it is difficult to compare an airblast gap to
other
> gaps, because the airflow significantly affects the breakdown voltage.
>
> IMHO, I like airblast gaps. They're reliable, can handle lots of power,
and
> are easily constructed. Downsides are that they're a bit hard to adjust
> (sensitive to spacing), require a source of high pressure air, and they're
> LOUD!!

Again I agree 100%. My airblast gap took me less than 20 minutes to make,
takes abuse from two mean MOTs, and still keeps going without a problem. The
gap on my coil will run for up to several minutes without decrease in
performance, even with the low voltage and high current I run. The spacing
is a little sensitive, but not that bad. As for the loud, I'll have to agree
with you. My neighboor lives about 400 yards away from me and he can hear it
every time I run my coil, with the doors and windows closed.

>
> As far as setting the gap spacing: I suggest turning the air on, and
placing
> your transformer (that you'll be using on your coil) across the gap. Just
the
> transformer itself, completely out of the coil tank circuit. Anyhow, turn
on
> the airflow and the transformer. If the gap doesn't break down, start
> decreasing the space between the electrodes until it does. You will be
> surprised how close the electrodes will be when it finally arcs over!!

I set my gap to fire just over what the transformers will do by themselves,
with the air on. Of course my cap is seriously overbuilt, and I'm not the
least bit worried about overvoltage.

>
> If you use it on your coil and the gap doesn't quench (big "flame" look to
> the gap, sputtery sound, poor coil performance, etc.), then you probably
need
> more airflow. The more power you run, the more airflow you need.

Again I totally agree with you. Your minimum airflow will depend on many
things, not just transformer output voltage. The material you use in the gap
is also very important. I currently use brass threaded rod in mine, which
works great. Tungsten is by far the best, and many types of steel really
suck and give bad performance. For example, I tried replacing my brass
electrodes with stainless steel, and my output dropped to nil, and there was
a shower of incandescent sparks shooting off the steel and hitting the
bottom of my primary deck.

>Just remember that, increasing the air velocity will increase the breakdown
> voltage. Coil components could be overstressed if you don't watch it ; )
>
> Hope this helps! Take care,
>
> Justin Hays
> KC5PNP
> Email: pyrotrons-at-aol-dot-com
> Webpage: www.hvguy-dot-com
>

Jason Johnson