Re: Secondary wire size concerns

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

Original poster: "Peter Lawrence by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Peter.Lawrence-at-Eng.Sun-dot-com>

> Hello list,
> Last night I finished some planning on my first coil.  The secondary will
be 12
> inches high, 3 inches in diameter and will need to be wound with 31 AWG.
That
> is .0089 inches in diameter (not including the insulation).  In theory (if
> wound perfectly) this would allow me to get 87.7 turns per inch for a
total of
> 1053 turns (insulation included).  Is this a common wire size used on
> secondary?  My transformer is a NST 7.5kv 20ma.  Should my secondary be
taller
> and my wire size be larger?  If this set up sounds ok, how much taller
should I
> make my secondary to account for the 'winding slop' that will inevitably
occur
> on my first wrap job?
> TIA
> --Green Horn

Green Horn,

I have made 5 different coils using #24, #26, #28, #30, #32 wire all on 3.5x12"
acrylic tubes, they all work!

I happen to get the best sparks from the smallest wire -> most turns. The 
difference ranges from 5" to 7" sparks with a 6kv-20ma NST.

You cant go wrong, just build it and then experiment from there if you like.

Get a torriod though, without one you will get lots of corona and sparks off
the top few turns of the coil, and with such fine wire you could even burn
the wire.  John Freau sells a Torroid that is a good size for your coil (I
have one on order myself).

I find that a sphere, if larger than the coil diam and if the coil winding
goes almost all the way to the top of the tube and if the sphere is sitting
on the tube (botton of the sphere is actuall below the top of the tube),
then you will not get too much corona off the top windings. What does not
work (for me) is the sphere mounted above the coil, like you see in many
pictures/drawings of TCs. I found nice 4" and 6" smooth hollow copper float 
value floats at a local hardware store, also in the MSC industrial machinery
catalog.

There are many tricks to getting the "winding slop" out of a coil, basically
it involves getting the kinks out of the wire as it goes on the tube. Forcing
the wire around any bend, like around a wood dowel, as it is being fed onto
to the tube, will eliminate the kinks. For wire this fine, I can eliminate
the kinks just by feeding the wire through pinched fingers (but with thicker
wire this will cut a groove in your thumb, so be careful!).

GO FOR IT!

-Pete Lawrence.