Re: Wire Size

[FutureT-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

In a message dated 7/31/00 3:56:44 PM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

> Wire Size
>  
>  What size wire should I use for my secondary. I have heard anywhere form
>  22-30 awg wire.  I was planing to make a 4x22 with 26 gauge or a 6x30 with
>  22 gauge. I will be using 15/60 NTS for power.  What size secondary and
>  gauge would be best for my power supply? I have heard that for small coils
>  big wire reduces spark length by 10%, I do not want high resistance to
>  decrease my coil performance. Below are the into on the 2 coils I could
>  build. :
>  PS Choke are thay in or out?
>  Coil 1:

Alex,

THe best wire size for your coil will depend on a number of factors.
For instance if you use a rather small capacitor with a static gap,
and therefore have to run at a high breakrate, then you can use
a smaller secondary and thinner wire.  If on the other hand, you use
a rather larger capacitor, then the secondary should be larger, since
the bang size will be larger, and the wire can be somewhat thicker.

A 15/60 NST in an optimal TC can give 60" to 65" sparks, so the
coil should probably be built to handle that in case you upgrade
later, or if you build it optimally to start with.  At a low breakrate,
the 22" tall secondary might be too short.  I had trouble with
breakdown with my 23" tall coil, powered by a 15/60, as the spark
length reached over 60" or so.  You probably need to make the
coil 26" tall to prevent the danger of breakdown if your sparks
reach 65" or so at a low breakrate.  (At a higher break rate, the
coil can be shorter because the bang size is smaller, but the
sparks will be shorter too.)

Now assuming you make the secondary 26" tall or taller, you 
can make it 4" wide, or you can make it 6" wide.  When all is said
and done.... it won't really make much difference in the performance.
I've tried both 4" secondaries and 6" secondaries on my coil and
got the same spark length.

If you do get 65" sparks, (you may need to use a sync gap to
achieve this), you'll probably be using a 6" by 24" dryer duct toroid,
or the toroid could even be slightly larger.  This larger toroid permits
you to use a somewhat wider secondary than would be advisable
using a smaller toroid.  The toroid has to overhang the secondary
a lot for best results.  A secondary that is too wide will shade too
much of the toroid and reduce the output.  Also, too much energy
will be trapped in the secondary (instead of the toroid) to give good
results.  What I'm getting at here is that a 6" dia secondary would
be OK for this coil design.  In a coil like this, I would not use 30awg
wire, but I might use 26awg if the coil is 26" tall.  Possibly I would
use 24 awg if the coil is 28" or 30" tall.  I would favor the thinner wire
(26awg) for the 4" coil, and possibly 24awg for the 6" coil.  I like to
use about 1600 turns on a narrow coil, but at least 1300 turns.  I'm
not sure how many turns you'll get in the examples I just gave, maybe
1200 or 1300 or more.  I left that task for you to figure out.  I'm just 
giving the overall picture here...the general concept if you like.

You may want to keep in mind that most coilers use thicker wire
with less turns.  I have tried thicker wire with less turns, but I got
shorter sparks in a number of direct comparisons.  The thicker
wire has lower losses, but secondary losses are not the entire
picture.  It is the entire coil... the big picture that must be looked
at.  Although the secondary losses will be a little higher using
thin wire, the overall coil losses will be lower.  This is because
the thin wire requires more primary turns to be used, which raises
the primary surge impedance and reduces the gap losses which
gives longer sparks.  Most of the losses in a TC are in the spark
gap.  Only a small amount of loss occurs in the secondary.  So
it's actually a trade-off.  Using thin wire in the secondary you get
a little more loss there, but you reduce the losses greatly in
the primary tank.... and get longer sparks as a result.  I obtain
10% longer sparks using the thinner wire.  The sparks are not only
longer, but fuller, brighter, more active, etc..... truly a wonder to
behold.

Important Note:

Using a lot of secondary turns will require the use of a lot of 
primary turns.  This can cause a problem using copper tubing
because the primary tends to get too physically large (too wide).
I deal with this by using 12 or 10awg close wound pvc insulated
wire primaries, but these are somewhat difficult to tap and tune.
If you do not want these difficulties, then you will have to use
the more common method of using thicker wire on the secondary
which lets you use fewer turns on the primary, which permits the
use of copper tubing to be more practical which makes tapping 
easier.

I use what I call the Six Keys to Efficiency:

Low bps, relatively small secondary with rather thin wire, large
primary inductance, good quality properly sized capacitor, and
properly sized toroid.  These methods are intended only for the
most efficient and advanced coils.  My smaller coil that gives
42" sparks from a 12/30 NST is at:

   http://hometown.aol-dot-com/futuret/page1.html

A better view of the sync gap is at:

  http://members.aol-dot-com/FutureT/TT-42index.html

Protective chokes should probably be avoided.

Cheers,
John Freau