Re: Surface Sparks = Wow!!
Sent: Sunday, August 03, 1997 2:43 PM
To: Tesla List
Subject: Re: Surface Sparks = Wow!!
You will find you will have to go to glass eventually as the high energy
spark streamers will begin to actually "melt" their way across the plastic.
This usually only takes about 1/2 hour of continuous operation before the
melted streamer paths begin to show up. Glass works just as good and can
be used indefinitely for this purpose. We made up a 7 ft. dia unit with a
variable speed drive for the shop -- we call it the "Eye of Thor" and use
it for demonstrations.
> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-poodle.pupman-dot-com>
> Subject: Re: Surface Sparks = Wow!!
> Date: Sunday,August 03,1997 12:15 AM
> From: Robert Michaels[SMTP:robert.michaels-at-online.sme-dot-org]
> Sent: Friday, August 01, 1997 3:11 PM
> To: tesla-at-pupman-dot-com
> Subject: Surface Sparks = Wow!!
> This message was originally addressed to ROBERT MICHAELS
> and was forwarded to you by ROBERT MICHAELS
> Unable to find tesla-at-puman-dot-com.
> Message was not sent.
> >From robert.michaels Fri, 01 Aug 1997 20:11:21 remote from
> Received: by online.sme-dot-org (Wildcat)
> id 29359W Fri, 01 Aug 1997 20:11:21 GMT
> From: robert.michaels-at-online.sme-dot-org (Robert Michaels)
> Subject: Surface Sparks = Wow!!
> Date: Fri, 01 Aug 1997 20:11:15 GMT
> Message-Id: <870466275-at-online.sme-dot-org>
> Organization: Society of Manufacturing Engineers
> To: tesla-at-puman-dot-com
> Dear People:
> This post is inspired by the several recent ones on the tendancy
> of spark discharges to follow a surface and evince a longer
> sparking distance than would be obtained from the same voltage
> discharging in free air:
> This surface-enhanced sparking can be exploited to make a very
> entertaining "appliance" for use with small to medium sized
> Tesla coils:
> 1) - Obtain a sheet of suitable insulating material.
> Most any will do, but let's say acrylic plastic
> ("Lucite"; "Plexiglas"; "Perspex"; et. al.)
> 2) - The effect is enhanced if the acrylic is black, but the
> backside may be painted if it is colorless.
> 3) - The size of the sheet is determined by the size of the
> coil, but let's say 4-ft. x 4-ft. for the sake of dis-
> 4) - The esthetics seem enhanced if the square sheet is cut
> into a circle of the same diameter, but this is immaterial.
> 5) - Drill a small hole in the exact center of the acrylic sheet
> 6) - Cut a circle of aluminum, say 1-ft. in diameter, more
> or less. Either light sheetmetal or heavy foil may be
> 7) - Paste the aluminum circle in the =exact= center of the
> acrylic sheet. You're on your own as to how to "paste".
> I use shellac because it is very traditional.
> I also use gutta percha (in other applica-
> tions) for the same reason -- but I digress.
> 8) - Make electrical connection to the aluminum circle thru
> the hole previously drilled in the acrylic plastic.
> An electical lead connected here will eventually connect
> to the business end of the Tesla coil.
> 9) - Form a length of copper tubing (or heavy copper wire)
> into a 4-ft. dia. circle.
> 10) - Precisely center this around the aluminum circle and
> adhere the tubing (or wire) to the acrylic plastic.
> 11) - Make electrical connection to the copper tubing. This
> goes to the rf-ground of the Tesla coil.
> 12) - Turn on the Tesla coil and let it rip.
> A hissing, snapping circle of sparks jumps from the perimeter
> of the aluminum disk to the copper tubing -- usually from
> dozens and dozens of places at once, continuously dying out
> and reforming in another spot, sometimes rotating around the
> disk perhaps first clockwise, and then counterclockwise.
> - - - - - - - -
> A four ft. piece of acrylic is a convenient size with which
> to experiment, but many a small Tesla coil will support 8-ft.,
> 10-ft., and even 12-ft. diameters.
> The hardest part in all of this is getting the perimeter of
> the aluminum disk everwhere equidistant from the copper
> tubing. If the two are not precisely on the same center,
> the sparks will tend to concentrate at the one spot where
> the two are closest. They will not rotate around the disk
> nor uniformly encircle it.
> In such event, the offending point on the aluminum disk
> may be trimmed off (gradually!) until the disk and the copper
> are equidistant. Use a utility knife for this if the aluminum
> is foil, else a Dremel "Moto-Tool" or the like.
> - - - - - - -
> This general idea of a disk surrounded by an encircling ring
> of copper comes from no less an august personage than Dr.
> Tesla himself, but ASFAIK Dr. Tesla mounted his disk and
> ring in free air and did not avail himself of the ability of
> a surface to greatly enhance spark distance.
> Sparking (and partying) on
> in --- Detroit, USA
> Robert Michaels