RE: Brass Ball static spark gap not doing so well

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

Original poster: "David Dean by way of Terry Fritz <twftesla-at-qwest-dot-net>" <deano-at-corridor-dot-net>

Hi Pete

Some folks will tell you that brass is the cats meow for spark gaps. My
experience has been otherwise. Probably due to the wide variety of brasses
and bronzes out there. All (true) brasses contain zinc, and some contain
lead. When the gap fires, some of the zinc is evaporated and makes metallic
ions which make the gap hard to quench. Your gap would probably work well if
the balls were made of pure copper, or silicon bronze (like the bolts for
marine and electrical use that you can get from McMaster-Carr). Finding pure
copper balls of any reasonable size is next to impossible, and if you do
find any, be prepared to pay for them.

I am building a crucible furnace so that I can cast some pure copper balls
for spark gap use. The furnace should be finished this weekend, ready to
fire next weekend. Perhaps in a few weeks copper balls will not be so hard
to find, or so expensive.

later

deano

> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Saturday, May 26, 2001 12:22 PM
> To: tesla-at-pupman-dot-com
> Subject: Brass Ball static spark gap not doing so well
>
>
> Original poster: "Pete Komen by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <pkomen-at-zianet-dot-com>
>
> Second light on my coil.
>
> Arcs not as long as they should be.  I think that the toroid is too rough;
> 20 inches across with 4" minor diameter.  Made of dryer duct not fully
> covered with aluminum tape.  Gives a number of streamers from the
> same 8 or
> 10 points.
>
> I have a new spark gap made of 15 - 1 1/8" brass balls spaced
> 0.022" apart.
> Air is blown around them but not specifically at the gaps.  Things started
> out OK, but the arcs kept getting shorted over a period of 10-15
> minutes.  I
> am running a 12kv, 60ma NST with protection circuit and 4 strings of 11 of
> the Panasonic caps for about 20nf.  The NST alone will jump 11 of these
> gaps.  When running in the TC, only 7 or 8 could be used without
> the safety
> gap firing.  Safety gap needs cleaning and a reset.
>
> When I quit tonight and dismantled the spark gap, the brass balls had a
> circle of black crust with a larger circle of tan around each sparking
> point.  There are pits in the brass itself (it looks like tiny
> balls pressed
> together with the areas between eaten away).  It seemed that the
> break rate
> had gone way up, almost to the point of power arcing.
>
> Question for Terry referring to your Terry gap at:
> http://users.better-dot-org/tfritz/terrygap.jpg
>
> It states that you use about 600v per 0.004 inch gap (60 pipe
> sections for a
> maximum of 58 gaps).  I am using a multiple section gap now.  My 12kv NST
> jumps 7 gaps of 0.022 inch (as close to that as I can set them).
> If I built
> a similar spark gap to yours, should I expect to use 28 gaps (12kv * 1.4 /
> 600v per gap) or 38 gaps ( 7 * 0.022 / 0.004)?  If it will only
> jump 28, why
> use 60 sections of pipe or would a smaller gap be better? 0.002
> inch maybe?
>
> More general questions:
> Does the optimum setting for a static spark gap, whether number of gaps or
> size of the gap(s), depend on the atmospheric conditions (humidity,
> pressure, etc.)?  My location, Las Cruces, is about 4000'
> altitude and very
> dry (desert).  Humidity of 50% is very high and very rare so I
> suspect that
> I could set a spark gap and forget it.  Would a Florida coiler (I lived in
> Palm Bay for a few years where the summertime humidity got as low as 78%,
> elev. about 20 feet) have to set the gap wider?
>
> As the number of gaps goes up, does the total gap go down?
>
> I looked at the Tesla Mailing List archives for spark gaps and
> somebody did
> an experiment that indicated that the single spark gap has a more
> consistent
> firing voltage.  Someone else reports longer arcs with multiple unequal
> gaps.  Someone else reports longer arcs with aluminum electrodes
> between the
> copper ones.  I am beginning to wonder what we really know about
> spark gaps.
> I know very little.
>
> Is a multiple small gaps spark gap better than a single gap?  Which has
> greater losses?  Which has the most consistent firing voltage?  Is there a
> spark gap that lasts longer between cleanings?  Is there an optimum static
> spark gap?
>
> I hope that I am not bringing up something covered already.
>
> Regards,
>
> Pete
>
>
>