Re: vacuum pump
The safety gap should be slightly larger than your overall static gap.
If it fires consistently, you need to make it wider so that it fires
only every once in a while. Start out with a lower power level until
you're in tune. I didn't have a variac at the time, so I shorted out
some of my gaps on the static gap until I was in tune, then gradually
Regarding vacumn pump, The hand pump auto vacs don't work very well but
could probably work. When I made my caps, the pvc end caps cracked due
to defective material (cheapo ace hardware end caps), so I couldn't use
a vacumn pump. I turned a hand sander (4" square Makita electric palm
sander) upside down and placed it on my workbench. Then I filled a cap
with oil (to within 3/4" from top), placed on top of sander and turned
it on. By varying the amount of pressure applied, the vibrations caused
the air to rapidly rise to the surface - the oil level quicly started to
drop as air was displaced by oil. By doing this for approx. 10-15
minutes on each cap, refilling as necessary, I was able to purge all air
out of the rolled poly.
I've been firing a 15K/60mA, 6.5" X 28" secondary with these caps and
getting some hefty sparks up to 36". Didn't know if it would work, but
it did-quite well I might add. I started firing the coil the same day I
did this and have not had any punch throughs from the voltage.
Hope this helps,
> Original Poster: "mike.shaw" <mike.shaw-at-the-spa-dot-com>
> First, I would like to thank everyone for the advice. I ended up making
> a rolled allum/poly cap instead of salt water. Now that I have it
> rolled and packaged in the PVC (what a pain!) I need to vacuum it out.
> I was wondering if a vacuum pump intended for auto repair would work for
> this purpose.
> I was also wondering how big I should make my safety gap. I am running
> a 12kv 30ma nst with a 4 in secondary, a 15 turn 3/8 in copper tube
> primary, and a 8 electrode static gap (.225in).