FW: SG electrodes

["Tesla list" <tesla-at-pupman-dot-com>]

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

Mike,
Try some resistance in series with your safety gap to limit the peak Cap
current.
Expect the resistor to get warm but your Cap will be thankful.
There is no Pri inductance limiter when the SG fires so peak current is
much higher.
There is no need to dump charge in such a short time w/potential adverse
affect on Cap life.
Regards, Dale

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com] 
Sent: Tuesday, March 27, 2001 5:53 AM
To: tesla-at-pupman-dot-com
Subject: SG electrodes


Original poster: "Mike Novak by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<acmnovak-at-msn-dot-com>

Hello All,

I've been making several spark gaps lately and got to thinking about
electrode shape/material.
I made a simple safety gap for a small cap bank using two brass barbs spaced
about 1" apart. I noticed that the electrodes dissipate a much larger amount
of heat than my main SG (consisting of  7 solid brass electrodes 1/2" in
diameter, 2 inches long sandwiched in between two pieces of oak clamped down
by four 1/4"-20 screws). The safety gap fires about once every two or three
seconds and exhibits about two times the wear of any one of my main SG
electrodes. I'm thinking this is because the safety gap is spaced further
apart thus creating excessive heat due to increased gap losses (seeing as
the arc spends more time in the air.) is this correct?
So I'm thinking, if one were to make their spark gap electrodes rounded
(even hemispherical) then the heating and overall gap losses would be
reduced. Would this effect be noticable on a SRSG ? I was thinking of
rounding my electrodes, but I thought I might bring it up before ruining a
perfectly good set of tungsten electrodes. Is there anything wrong with my
assumption?
Also, would it be easier on the tank gap if the safety electrodes were
pointed? The gap losses would be raised and the tank cap wouldn't see such a
violent surge...
Another point I thought I'd touch on is the material of which the electrodes
are made of. For one thing, I don't see why everyone insists on using top
dollar tungsten electrodes on coils less than 5-10kW. The SRSGs I've seen
have VERY little heating. I don't see why one couldn't use aluminum or any
other low loss conductor for that matter. The gap mentioned above had small
deposits of carbon on the sparking surfaces, but other than that, showed no
sign of wear. The carbon deposits can be wiped off with one's finger...
Although it should be noted that the coil was running 500 VA with a STR cap.
It seems to me that gaps really need to evolve at this point. I'll be taking
part in some inert gas SG research over the next few months depending on
time/money. Does anyone have any suggestions as far as gases and electrodes
here?

Keep on thinkin'...


-Mike Novak