Re: Quench Improvement
Sent: Saturday, August 09, 1997 4:49 PM
To: Tesla List
Subject: Re: Quench Improvement
I agree completely with your accessment of brass. We use 1/2 dia.
tungsten/molydenum alloy that threads into a 1/2 dia x 1 1/2 inch long
brass rod (axially thru the G-10 plate). Even RF currents appreciate the
old axiom that "maximum current is limited by the highest resistance
element in the circuit" and many times this tends to be the steel or
stainless steel use in RSG construction. RF currents especially abhor
steel. The net result is that while the streamers are nearly as long
(indicating only a slight loss of potential) they are not nearly as bright
indicating a reduction of peak current in the spark channel. Steel and SS
do work ok in small systems but the results are substantially different as
your rise above the 5-7 kva level.
> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-poodle.pupman-dot-com>
> Subject: Quench Improvement
> Date: Friday,August 08,1997 11:21 PM
> From: Chuck Curran[SMTP:ccurran-at-execpc-dot-com]
> Sent: Friday, August 08, 1997 8:08 PM
> To: Tesla List
> Subject: Quench Improvement
> Hello All:
> 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!
> Chuck Curran
> Cedarburg, WI