Re: Secondary Spec

Subject:  Re: Secondary Specs
  Date:   Wed, 16 Apr 1997 12:47:48 -0400 (EDT)
  From:   Esondrmn-at-aol-dot-com
    To:   tesla-at-pupman-dot-com

In a message dated 97-04-16 05:26:23 EDT, you write:

 I am about to build my _first_ coil.  Initially it will be powered by a
 12kV 30mA Neon, but I'd like to build a coil capable of coping with
 whatever other bigger transformers I might get lucky enough to come
 across for a while.
 So at this stage I'm thinking of a 10" diameter secondary, on some
 'nice' plastic, not PVC.  I'd like to wind it with about #18 or even
 wire.  #18 gives about 34" winding length for 800 turns & about 42" for
 1000 turns, close-wound.
 I haven't given the primary much thought yet  - probably about 1/4" -
 1/2" copper tube (What's the advantage of 'conical' primaries ?)
 So I just wanted to draw on the pool of knowledge & experience here, &
 see what comments anyone has about my suggested dimensions, etc, before
 I go and spend the bucks !
 Anyone care to hazard a guess as to the performance of such a coil,

I would recommend a flat spiral primary.  I have built both types.  I
think the original idea with the bowl shaped primaries was to increase
coupling.  Flat primaries offer plenty of coupling.  Bowl shaped
primaries just raise the outside turn (and then the strike rail) several
inches closer to the toroid and cause problems with strikes down into
the primary.  If you are going to stay with 12 kv  30, 60 or 90 ma
transformers, 1/4" copper tubing should work fine.  If you plan to use
power levels above that, I would use 3/8" tubing with 3/8" spacing.  Try
to get about 14 turns on the primary to allow for a large tuning range
which will come in handy in the future as you work with various
capacitor and toroid combinations.

A 10" diameter coil is sort of large to start out with, I am assuming
this is you first coil.  With even a small 12 or 14" toroid, the 12kv 30
ma transformer may not provide enough power to cause breakout.  You
might be better off with a 6" or 8" secondary.  My first coil was  6" x
27.6" wound with #22 wire.  I got 34" discharges with one 12 kv 60 ma
transformer right out of the box, so to speak.  It now utilizes a 5 kva
pig for power and produces 80" sparks.

Have fun.

Ed Sonderman