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Re: Surface Sparks = Wow!!
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
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>From robert.michaels Fri, 01 Aug 1997 20:11:21 remote from online.sme-dot-org
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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-
cussion.
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
used.
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