From: Chuck Curran[SMTP:ccurran-at-execpc-dot-com]
Sent: Friday, August 08, 1997 8:08 PM
To: Tesla List
Subject: Quench Improvement
I recently changed my spark gap and the results proved to be of great
interest to me because of the positive results. I wanted to post the
results, since it clearly supports the on-going thread relative to the
critical nature of spark gap quench times.
My new system this year was running with bigger sparks than my system
built last year, so I was initially pleased. However, since I was
drawing 60 amps at 280 VAC into the pig primary, the efficiency was
pretty poor for 11'-13' sparks. I decided that I could consider
changing coupling, primary tune, or the spark gap for possible
improvements. My gap had pretty wide electodes in the stationary pair,
so that is why it was suspect. Bert Hickman had seen the system run so
I did run my options past Bert too and the spark gap got the vote.
My gap provided a "mechanical" dwell of 265 usec when I started.
However, as I examined it closer it was clear that the spark had been
"dragging" beyond the flat face and up the taper that exists on my brass
electrodes. The discolored and heat checked section was around 11/16"
long. The dwell must have really been very high during operation,
approaching 500 usec.
O.K., my selected path was to drill and ream the original 1" diameter by
1.25" long brass stationary electrodes (with a taper down to 3/8") with
a .125" diameter hole and added a 6-32UNF set screw at a 90 degree angle
to the axis. Here a 1/8" diameter section of tungsten was inserted,
1/2" into the brass and 3/8" extending beyond. At the power I was
running I really didn't expect it to last, but it was a start. This
would result in a mechanical dwell of about 88 usec. The air gap was
.025" here and in the vacuum gap electrodes.
Well, I fired the system up and it ran great for 2 minutes and 40
seconds and then I stopped and checked out the tungsten. (Neighbors
came out of the woodwork everywhere.) It looked just like when I
started--it appears that the brass did do an acceptable job of heat
sinking the tungsten. I ran it again and I really got the best sparks I
have ever seen on my system over the next run. It's my opinion that the
improved quench has made a very positive change.
Now for the best part. I originally was drawing 60 amps with the big
electrodes and now power comsumption dropped to 42 amps with better
spark! My rotary currently has 12 rotating electrodes and runs at 2250
RPM, I may consider removing 6 electrodes and running at 4500 RPM for
better quench times yet.
I've gained alot of respect for the work done by others associated with
quench times. The impact on my systems performance was extremely
positive, based on one run. I will be setting up again and trying to
see what kind of arcs I can draw, but things do appear better now!
Thanks to Bert Hickman for his advice, I just had to cook some
hamburgers and brats on the grill for all that night!