[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

FW: vacuum spark gaps



Original poster: "Dale Hall by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Dale.Hall-at-trw-dot-com>


Hi Jason,
I've been using Jennings & Kilovac vacuum relay spark gaps for ~3 years
with great performance for low BPS.

A Vacuum is a perfect insulator - sucks out leftover contact material quickly
allowing optimum quench and keeps electrodes shiney (no oxidization). 
Nothing is perfect: as break rate increases so does 
tungsten deposits on the glass envelope (insulation resistance decreases)
and beyond some BPS, heat removal becomes difficult.
I use the largest glass path types.
Some "contactors" employ a metal cup around the contacts effectively 
keeping vaporized metal from depositing on the glass envelope.

Some vacuum switches (antenna sw) have a flex metal armature, 
allowing precise fixed gap adjustment.
But mostly I use single shot mode and manually control discharge
by applying a charged cap (~70v 10uF) across the 26v rated coil to 
jog the tungsten contacts w/o touching, to prevent welding/sticking
due to the high peak current.

---------------
My single shot DCTC:
Single shot Arcs over hard (non arc participating) dielectrics restrict
discharge to 
2 dimensions increasing statistical probability of producing a max length
power arc.

Current Specs, performance:
Ctop ~25pF 8" x 20" galvanized toroid
Lsec 30mHy 6.5" dia 20" long white PVC form
Lpri 3.4uHy 1/4" Cu tubing, spiral, 16" OD (tap outside in)
mutual coupling coefficient adj .18 to .22
Cpri .2uF 10kvdc 4.9J per bang
Vpri 7kVdc via 12v dc-dc flyback converter from 1.5" BW video camera
monitor, 50mA quiescent
GAP = commercial Jennings/Kilovac vaccum relay implementing unique 'jog' method
Vout-pk = Vpricap * sqr(Lsec/Lpri) * efficiency
Vout-pk = 7000 * sqr( 30mHy / 3.36uHy)*.8 = 529,150 Vpk (theoretical maximum)

Power Discharge point to point maximum to date (7/4/00) = 38"+ 

Easily scaleable up or down (add or remove .1uF caps, adj Pri tap)

Arcs are generated in front of hard dielectric: glass, plastic, masonite, 
(dielectric does not participate in arc gases as evidenced by it visible
spectra = that of N2, O2)
to encourage arc path to 2 dimensions (Vs 3 dimensions in the dielectric
Air, 78% N2, 21% O2)

original DCTC picts: 
.1uF 7kV 2.45J
12v to 7kVdc converter, Sparks, scope field V & Iarc waveforms, trick or
treat '99 photos:
photos: D300 Olympus 1024x768 and a calibrated button finger 
(capture ~1 of 8 due to "no bulb" on digital cameras)
see photos of components & arcs:
 http://www.cowmail-dot-net/dalehalldctc/

 more recent 38" discharges are at new Terry Fritz site:
 http://hot-streamer-dot-com/TeslaCoils/Temp/09balPwr%2B2branch37inGud.jpg
	/12balPwr%2B3br35inGud.jpg
	/15balPwr37in.jpg

BTW: the DC-DC converter can be designed for higher current (or V) output
which can  
drive higher BPS (alternate gap design) at the cost of complexity, cost and
input power.

Regards, Dale 
Redondo Beach, Calif.
dale.hall-at-trw-dot-com

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com] 
Sent: Wednesday, December 13, 2000 7:39 PM
To: tesla-at-pupman-dot-com
Subject: vacuum spark gaps

Original poster: "Jason Johnson by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <hvjjohnson13-at-hotmail-dot-com>

Will vacuum spark gaps work in a tesla coil? I've got two that fire at around
2kv each and I would like to use them in a small coil. Maybe powered by a small
electronic NST. Any ideas on effiency w/ vacuum gaps? The idea of a silent
spark gap is rather interesting compared to my airblast gaps on my MOT system
which sound like an unmuffled chainsaw.
 
Thanks Jason Johnson