Secondary coil arcing to itself

From: 	Kevin Christiansen[SMTP:kevin+-at-cs.cmu.edu]
Sent: 	Thursday, June 26, 1997 7:25 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Secondary coil arcing to itself

Hello everybody!

I just put togeather a small Tesla Coil that is exibiting

a behavior that I have never seen before:  the secondary 

coil arcs to itself at various points along its length.

Basically, an arc will break out somewhere along the length

of the secondary, streak up (or down) the secondary for 2 to

4 inches, and then re-enter the secondary.  While these little

arcs playing all over the surface of the secondary are certainly

neat-looking, I am sure that they are murduring the insulation on

the wire and are robbing me of power.  (Note that these are NOT

torroid-secondary, primary-secondary, etc. arcs - these arcs just

streak from here to there along the surface of the secondary.)

Any suggestions on how to stop them?

(I have a can of that 2 part Devcon Flexane Urethane rubber

stuff, which claims a dielectric strength of 350 volts/mil.

Should I glop a thick layer of that over the top of the


Here are the specs on the coil, for those that are interested:

Power supply

  7.5 A variac

  15 Kv 30 mA neon

  misc RF protect chokes, protect gaps, etc.

Primary tank

  .005 uF, 60 Kv energy storage cap by High Voltage Components, inc.

  12.75 turns of .08" house wiring: 5" tall and 10.5" diameter

    Wound on a plastic bucket

  .25" static gap, in 10 to 40 equally sized "mini-gaps".

    Tungsten carbide electrodes


  #24 magnet wire: 17.75" tall and 4" diameter, close-wound

    Wound on a PVC pipe that was sanded, heated, and painted

    with several layers of oil-based polyurethane varnish.

    Coil was varnished after winding as well.

  Torroid is 3" Al dryer duct, 12.5" wide


  About 30' of Belden 8213 heavy 0.5" coax, using both the shield

  and the center conductor, clamped to the plumbing system of my

  appartment in 2 different places.

Currently, I am getting 14" arcs from a small wire taped to the side

of the torroid, to ground.  How long of arcs should I be able to

get out of a 15 Kv 30 mA neon?

Thanks for any suggestions/comments that you can give me!


                     Kevin D Christiansen

Human Computer Interaction Institute - Carnegie Mellon University

      kevin-at-cs.cmu.edu    http://www.cs.cmu.edu/~kevin/

"The universe is composed of space, galaxies, and intergalactic

 dust.  Galaxies themselves are composed of space, stars, and

interstellar dust.  From the omnipresence of dust, we conclude

that nature abhors a vacuum and won't pick up a broom, either."