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Re: [TCML] Dual identical FRANCE neon sign transformers (15000v 60mA each) in parallel


The secondary does not need to be as tall as the spark is long.  For example
my TT-42 coil has an 18" tall secondary and gives 42" sparks.  However sparks
are more likely to arc down from the toroid and strike the primary if the secondary
is too short.  I often place a smaller toroid below the main toroid to raise up
the main toroid some to keep sparks away from the primary.  The length
of the sparks has a lot to do with the current in the arc and the growth
of sparks over successive gap firings.  It seems to me that a high spark
gap break rate coil could tolerate a smaller secondary than a low break
rate coil for a given input power, because the "bang size" (joules per
gap firing) is lower in the high break rate coil.  As far as I know no one
has ever really researched this.  It was the next thing on my list but
I never got around to it.  I usually prefer low break rate though because it can
be more efficient in the sense of producing longer sparks for a given
input power in a properly designed coil.  High break rate has it's good
points too though.  

Generally speaking, when the power is increased, the coil is made larger
in proportion.  If you use 4 times the power, then the coil should be twice
as large in all proportions including the toroid (assuming the coil was sized 
correctly in the first case).... square law sizing concept.  As you said, 
the wire should generally be somewhat thicker for higher powers.  

The 22 gauge plastic insulation wire will work, but may result in the use 
of fewer primary turns, which increases the spark gap losses somewhat 
due to the non-linearity of the arc resistance.  Plastic insulated wire will
also run at a higher frequency which generally results in shorter sparks 
also.  Generally the magnet wire is a better choice.  Very large coils 
may better tolerate the plastic insulated wire however.  



If I use both 15kv/60mA NSTs (yes they were identical and phased the same
with my jacobs ladder - bigger flame spark), then the sparks could be 4-5
feet in length so shouldn't the secondarys also be 4-5 feet tall. All of
the designs I see are about 2 feet for the secondarys but are wider in
diameter like 4" to 6" or more. This doesn't make sense to me. Why go wider
in diameter and not taller in the secondary? I would think you would want
thicker wire like 22 or 20 gauge wire and not 24 or 26 gauge. Also does it
have to be magnet wire. Radio Shack 22 gauge wire has plastic like
insulation. Is that ok?




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