Re: Coil Hight

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

In a message dated 7/28/00 3:57:28 PM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

> Original poster: "Alex Madsen" <alexmadsen-at-netzero-dot-net> 
>  
>   
>  
>  Is there a general formula or something to determine the optimal height of 
> an
>  Tesla Coil. I know that it is a good idea to keep a 1 to 5 high to 
diameter.
>  What is the ideal wire gauge. My power supply will by a 15kv 60 ma.

Alex,

>From a coil voltage breakdown perspective,
the ideal height depends mostly on the bang size (joules per
gap firing).  For instance at 120 bps, a coil should be taller than
24" when giving a 65" spark.  However, at 300 bps, a 24" coil is
fine for a 65" spark.  

Another issue is that if the secondary is too short, the sparks
will tend to loop down from the toroid and strike the primary.
For instance my 42" sparks from my TT-42 TC sometimes hit
the the primary.  

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

Using my taller (24") secondary, the sparks do not hit the primary,
when giving 42" sparks.  

another factor is how wide the toroid is:  A wider toroid will tend to
direct the sparks outward.... with less tendency to loop down to
the primary.  You can certainly go as tall as a 1: 6 ratio.

Regarding wire size,  I prefer to use a somewhat thinner wire than
usual, because this generally gives longer sparks.  I use #28 wire
for my TT-42 TC which gives the 42" sparks.  By using thinner wire
you can get a lot of secondary turns, I like to use about 1600 turns.
This keeps the secondary small and compact, with high inductance,
and keeps the gap losses low.  (most of the losses in a TC are in
the spark gap, so it's very important to keep the losses as low as
possible).  Generally, using a thinner wire will give you about 10%
more spark length.  I haven't mentioned it lately, but not only will
the sparks be longer, but brighter, and more full all around the
toroid.  Simply by using thinner wire on a secondary, with more
turns, and a smallish overall secondary size, the coil can behave
like a completely different, more powerful coil.  When I put a 
secondary on my coil that has thicker wire with less turns, the
decrease in performance is shocking to say the least.

To tune the coil, when there are many secondary turns, a lot of
turns in the primary will be needed also.  I would suggest maybe
#26, or #24 wire for your TC.  The height would depend on the bps,
but maybe 28" or a little more.

Cheers,
John Freau