Re: Rotary Spark Gap - Construction Questions

["Steve Young" <youngs-at-konnections-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Ross,

Several have good success using an angle grinder for their ARSG.  You get a
bonus of a built-in means for mounting your rotor disk.  Angle grinder
motors usually are Universal AC/DC motors.
--Steve

----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, July 28, 2000 4:23 PM
Subject: RE: Rotary Spark Gap - Construction Questions


> Original poster: "Basura, Brian" <brian.basura-at-unistudios-dot-com>
>
> Ross,
>
> A "Universal" motor has brushes. When searching for a used one look for
> large power tool motors, washing machine motors, etc.
>
> If you are going for a new one then check out Dayton's 1/2hp model
> http://www.grainger-dot-com/cgi-bin/item_detail?1847044Y2M145
>
> They also make a 1-hp model
> http://www.grainger-dot-com/cgi-bin/item_detail?1847044Y2M191
>
> Regards,
> Brian B.
>
> -----Original Message-----
> From: Ross Overstreet [mailto:ross-o-at-mindspring-dot-com]
> Sent: Thursday, July 27, 2000 6:02 PM
> To: Tesla List
> Subject: Rotary Spark Gap - Construction Questions
>
>
> Hi Gang,
>
> I have a new project on the drawing board.  I want to build a 10"x45"
> secondary, PT powered coil that will be operated primarily in DC mode.  I
> would also like to run it as an AC coil, but I'm willing to do several
hours
> of work to reconfigure (I don't care to do all the initial design work so
> that it will be an easy swap-over.  I don't mind having 2 sets of caps, 2
> rsgs, etc).
>
> My main design challenges right now are the rotary spark gaps for a large
> system.
>
> ----ASRG----
> I'm looking for nice speed controlled gap from 0 to about 800 breaks per
> second.  I'm half-way basing my desgin Kevin Ottalini's DC coil that does
> well all the way out to 700 bps.  After reading lots of TCML archives, it
> appears that the ideal motor for such a task is a 1/2 to 1 HP "Universal
> Motor" that apparently can be run on either AC or DC.  Chip mentions that
he
> uses one of these on his gap
> http://bhs.broo.k12.wv.us/homepage/chip/details.htm
>
> I don't know anything about this type of motor.  Can someone suggest
> sources/costs for such a motor?  I will probably wind up using a phenolic
LE
> rotor with 3/16" tungsten rod electrodes.  Looks like 6000 RPM with 8
> electrodes can get me the 800 bps I desire.  Don't worry with sending the
> usual safety alerts - all will be cut on a good mill, statically balanced,
> contained, etc.  I can use any advice/links on high speed ASRGs and
> universal motors.
>
> ----SRSG----
> I also plan to build the typical SRSG using a design similar to the ones
> shown in the links below.  This design seems to be what many of the
> professionals and big-coil hobbyists have settled on.
>
> (TTR design) http://www.ttr-dot-com/rotary_spark_gap.htm
> (*) http://www.foxtail-dot-com/Teslathon/D1/DSCN0007.JPG
> (*) http://www.foxtail-dot-com/Teslathon/D1/DSCN0006.JPG
> Brian Basura design: http://fp2.hughes-dot-net/brianb/rsg.htm
> (*=TTR design on display SoCal Teslathon 2K, photo by Jody Kravitz)
>
> There is an abundance of info on the web about this type of design, but
> there does seem to be one magical problem - what sort of dwell time works
> out best.  (ok, ok, I don't want to start the mechanical dwell not equal
to
> electrical dwell argument so from here on out I'll just call it electrode
> overlap)  I know that this is power throughput dependant, but maybe we can
> agree on some ballpark figures for coils driven from PTs or small pigs.
> This question comes up after seeing one of my buddies almost attack his
SRSG
> with a sledge hammer.  The initial design used .375" electrodes all the
way
> around.  This made the electrode overlap a little over 1000us.  The coil
> would barely run.  After changing his rotating electrodes to 1/8" and
> offseting the stationary electrodes a little, he got the overlap down
around
> 500us.  This made a world of difference in his coil!  Now Brian's coil is
> one of the hottest 6.5" sec, PT powered coils out there!
>
> Has anyone else stumbled across electrode sizes or overlap times that
worked
> really well on this size system?  Are there upper/lower limits that should
> be used early in the design stages? I have read that 1/8" stationary
> electrodes don't work too well on 5KVA or above coils due to overheating.
> Unless I'm doing my math wrong, most of the well performing gaps that I
> reverse engineered from the photos on the web all have electrode overlap
> times around 500us.  Ideas?
>
> Making arcs in SoCal
> Ross-O
> http://users.better-dot-org/roverstreet/
>
>
>
>