Re: Need Help with Large Tesla Coil

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

Original poster: "Steve & Jackie Young by way of Terry Fritz <twftesla-at-uswest-dot-net>" <youngs-at-konnections-dot-com>

Jonathan,

1) non-skid winding:  Run a bunch of strips of double sided scotch tape
along the length of your secondary.  That keeps the windings secure and
doesn't mess up performance.

2) Rhino-coating:  Get a scrap sample of rhino coated cardboard to simulate
your secondary form.  The sample can be a strip about 1 x 8 inches.  Connect
your pole pig with some ballast in series with the low voltage side of the
pig.  A toaster or electric heater will work fine as a ballast (you don't
need any output current, so a resistive ballest will be fine.)  Hook one end
of your rhino-strip to the high voltage side of your pole pig (ground side
if it is a one-horn pig).  Attach the sample to a couple feet of PVC pipe to
insulate you from the sample.  Turn on the pig, then VERY CAREFULLY bring
the other end of the rhino-strip close to the other pig HV terminal.  If you
get an arc to it, then bad news - forget about using your rhino-coated
sonotube.  If no arc, then the rhino is not conductive, so wind away!  Note
this procedure is DANGEROUS - be careful!  The toaster-ballasted pig is very
lethal.

If you have a neon sign transformer, this would be easier to use and would
not require a ballast.

Why not just use an ohm meter?  The HV method tests for suspended conductive
particles (like carbon) in the rhino coating which an ohm meter would not
detect.

3)  Winding length:  #22 wire gives you about 37.5 turns per inch.  So 1000
turns is about 27 inches, and 1500 turns is 40 inches.  What you are after
is a winding length of around 64 inches for your 6 foot sonotube.  So,
either use bigger diameter wire, or space wind.  If you bifilar-wind your
coil with two lengths of #22 wire, you will end up with around 1200 turns,
which is a good number.  Then you can carefully unwind one of the wires,
leaving a space-wound secondary.  Be sure to coat it with polyurethane or
such to hold the turns in place.

4) I doubt the spacers will be needed - you should be able to get at least
12 foot arcs without secondary flashover if you have proper field control
via your toroid top load and you don't over-couple to your primary.

5) If this is your first coil, consider making it your second coil!  You
ought to get your feet wet with a much smaller coil to gain some experience
with construction techniques, tuning, coupling, spark gap operation, etc.
--Steve

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, April 19, 2001 8:15 AM
Subject: Need Help with Large Tesla Coil


> Original poster: "Jonothon J. Cawley by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <cawleyjj-at-physics.purdue.edu>
>
>    Hi, I am a college student at Purdue University where I am attempting
> to
> build a large tesla coil. Currently, we have 3 Pole Transformers, 8 mi. of
> #22 magnet wire, and a 6 ft. long by 18 in. dia. sonotube as a secondary.
> My immediate concerns are with the coating and winding of the secondary. A
> friend and I recently took the sonotube to a Rhino-coating place, they
> coat truck beds with a black plasti-like compound. The workers there
> coated the sonotube. Now, I would like to know if this is a good coating
> for a large tesla coil secondary. Next, how should I prepare the coated
> sonotube to make sure the wire doesn't slip off as I am winding. Another
> question along these lines is how should I wind the secondary? Should I
> close-wind it or should I space wind it? What exactly is space winding?
> Furthermore, should I install 1/4thick by 3 ft. diameter "spacers" along
> the length of the coil in order to suppress arcing from the toroid to the
> lower secondary turns? Any help would be greatly appreciated. Thanks in
> advance for any help or advice.
>
> Sincerely,
>
> Jonothon J. Cawley
>
>
>
>
>