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Re: Rotary Gap Construction?



Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 3/20/02 4:19:32 PM Pacific Standard Time, tesla-at-pupman-dot-com
writes:


>
> Hello hello,
>     My last coil used a static spark gap with marginal results at best, so
> I'm
> planning out a means of building a rotary gap.  Since many of you seem to be
> experts in construction, I was wondering if anybody would mind throwing in a
> few engineering suggestions.  I'm open to anything, and have a substantial
> budget to work with.  I'm looking around for 2400-4800rpm variable motors
> (most of them I can just control the angular velocity with a variac, right),
> I'm assuming that this should be enough if I have about 6-8 presentations
> every rotation.
>
> What I'm having difficulty with, as of now is:
> 1) My idea calls for using a conductive circle with bolts attached as the
> electrodes.  I would then have two stationary electrodes (one at the 9:00
> and one at the 3:00 position).  The problem I see in this is that the
> charge, as it passes through the metal disc, will also partially hit the
> motor.  This is bad.  Is there a way to, say, using electrical tape, wrap
> the circle around the center with tape, or would this not work?
>
> 2) This would be slightly more complicated, but I suppose I could use a
> belt, run off the motor and connected to the electrode plate, thus the motor
> would be insulated from the electrode plate.
>
> 3) I'm also worried about the heat from the sparks melting the bolts... I
> don't think those viewing the demonstration would appreciate a "hot dross
> bath"... is there something (like tungsten?) that I should coat the
> electrodes in?
>
> As of now, I'm looking at the following for my setup:
> a combination of the following transformers:
> One 15kV 60mA neon
> Two or three 12kV 30mA neons
> Combination of the above... suggestions welcome here too.
> Everything through a 20A 0-120V variac.
>
> 2 .018uf capacitors (in parallel)
> 12 turn flat primary spaced 1/2"
> 8" x 32" secondary, 24AWG topped with a 14x4 aluminum toroid (may build a
> larger toroid).
>
> The circuit is in the simplest design... Vac through primary transformer in
> parallel with main spark gap. (two chokes to protect transformer).  Tank
> circuit standard.
>
> Thanks much, I'm still fairly new to coil construction, so I apologize in
> advance for my ignorance :).  Strangely enough, none of the professors here
> have had much HV experience, so I'm more or less on my own with this
> project.
>
> ><>Matt Meyer
> meyerml-at-stolaf.edu
>
> ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>
> Matt "Woody" Meyer         Ellingson 120       507-646-2883 (CUTE)
>
> St. Olaf College Physics Major
> St. Olaf Admissions Tour Co-Coordinator
> 2001-2002 Ellingson Hall Residence Life Junior Counselor




Matt,

Your coil project and design sound fine.  I would not recommend using chokes
for transformer protection.  They do more harm than good.  I would suggest
instead using Terry's protection system, it seems to be popular.  I use only
resistors in series with the H.V. supply lines, between the transformers and
the spark gap.

For the synchronous rotary, you really need a synchronous motor.  Either
manufactured that way, or modified armature to make is synchronous.  The rotor
itself does not need to be conductive.  It is easier to manufacture if it is
not.  Mine is 1/2" thick phenolic with four brass electrodes with tungsten
faces on them.  I bought the motor, rotor and electrodes from Bill Wysock (on
this list).  Then I made a mounting base and electrode holders and completed
the project.  You can see this gap at my web site:
http://members.aol-dot-com/esondrmn/index.html

Good luck, Ed Sonderman