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Re: Primary/sec'y spacing for my big coil. (fwd)





---------- Forwarded message ----------
Date: Mon, 3 Aug 1998 20:07:45 -0600
From: terryf-at-verinet-dot-com
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Primary/sec'y spacing for my big coil. (fwd)

Hi Clay,

        My comments are added below:

At 10:07 PM 8/2/98 -0600, you wrote:
>From: Larry Bud Melman <gasman-at-althea.a-line-dot-net>
>To: Tesla List <tesla-at-pupman-dot-com>
>Subject: Primary/sec'y spacing for my big coil.
>
>	Hi all...
>
>	Finally got my coilform for my coil - using a 16 inch sonotube,
>sealed with urethane varnish, and going to reinforce with fiberglass cloth 
>and resin, since I suspect 3500 ft of 14 gauge wire is *pretty heavy*...

44 pounds according to my chart!!

>
>	Thinking about overall design, and when I was planning the primary,
>I realized that I wasn't sure how large I should make the space between primary
>and secondary.  Don't wanna make it too small, but obviously will get more
>spark from coil if I can minimize it... (I was planning a flat, archimedes 
>spiral - sound good??)
>

A flat coil should work fine and be easy to make.  I would make the turns of
the secondary so they are level with the turns in the primary.  Then, if
needed, you can simply raise the secondary to reduce the coupling.  I can
calculate the coupling for you to about 1% but I need a little more info on
the primary.


>	I'm thinking about 2 inches space.  Whaddya all think??

That should be fine.  It will prevent sparking but give good coupling for
the large diameter secondary your are using.

>
>	Tentative specs of coil:  using 10 kVA PP, 23 kV (27 if using 280v
>input)
>
>	--height of windings 54 inches (800 turns) - sec'y inductance 73.01 mH
>
>	--Approx resonant freq 110.8 kHz
>
>	--Tank cap: 50 kV 0.05 uF ($375 at SurplusSales-dot-com - OUCH!!!!)
>				  (geez - only gave $250 for my reconditioned
>				   pig with non-PCB oil)
>
>	--Primary: using 1/2" (12.7 mm) copper tubing, 8 turns, should tune
>between 5 and 6.


If you send me the spacing between turns, the inner radius, and the outer
radius, I can tell you the coupling.  
        My gap gives the best quenching I have seen.  Better than rotaries
and vacuum gaps.  However, it will not handle the pole pig.  It is really
for a single neon (1KW).  This weekend we found that different gaps and
firing voltages do affect the output character greatly.  I am building a gap
that can handle high power and explore these issues.  It will be very
adjustable and versatile.  It is about two weeks away from being a real
object.  It will have all the best properties of the gaps I have seen.  I
think the gap is THE most important part of the system.  There is much to be
learned about gaps and my approach is to make a high powered gap that can do
it all.  More to come.

>
>	--Sparkgap:  I'm blazing the trail with a Terry Fritz gap on this
>relatively high-power coil, planning 5 thousandths gaps times 50 or 60.
>I will do most anything to avoid the dreaded and feared RSG.
>

My present gap design cannot take a 10KVA pole pig.  It will overheat and
die.  I am working on a much higher power gap but I haven't built it yet.
Basically, it draws air through the gaps from the bottom through slits with
a shop vac and has fans on the top to cool the tubes.  I am also going to
3/4 inch tubing 3 inches long and around 6 mil gaps to prevent clogging.
Still some design work to do.  I hope to make the tubes easy to rotate and
clean.  This gap should handle the power levels you are planning.  It should
have excellent quenching, easy adjustability, and provide safety gapping all
in one unit.  It is a little complex but nothing will be critical.


>	--Topload: beats the hell outta me.  I figure this thing will take a 
>toroid in the 48-inch range.  I have no idea where to get one.  Try some
>muffler shops maybe - I remember that thread.  They'd be awful skinny though.
>Need a bigger X-section.  Probably end up with heating duct.

Big heating duct.  Check out the heating contractors that work on commercial
buildings instead of the "home center" places.  They can get very wide
aluminum flex duct.  Perhaps a little expensive but they can get anything
you could ask for.

>
>	I'll be mighty disappointed if I can't get 10 - 15 foot sparks from
>this one...time to start wining and dining the neighbors...
>
>
>						Clay   8-}
>
>

Best of luck!!

        Terry Fritz