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Re: Designing Demo Coil

Original poster: FutureT@xxxxxxx In a message dated 8/11/06 2:00:27 PM Eastern Daylight Time, tesla@xxxxxxxxxx writes:

I found the equation for maximum spark length (1.7 *
Sqrt(input power in watts)), and that suggested a 450
watt system should do the job (a 15/30 NST).  How
optimistic is that?  Should I go for something larger?
I may be able to do a 12/60 system, depending on what
I can scrounge from the local sign shops.  (I already
have one 12/30 that seems to work fine, albeit with a
slight buzz--I don't know why it was discarded.)  I've
read a fair amount here, but have no practical
experience yet.  I'm not sure just how efficient my
first coil will be, so I don't know how much power I


My TT-42 coil which can be seen at my website uses
a 4" x 19" secondary and gives about 42" sparks using
a robust 12/30 nst.  Using a normal 12/30 nst it gives
38" sparks.  I use a synchronous rotary gap for good
efficiency and good looking sparks.  Using a static
gap, some spark length would be lost.  If you build your
coil similar to mine, then it will be just as efficient.  The
design is not super-critical.

I was also planning on using a 4" secondary since I
have the pipe, but I haven't settled on the other
parameters yet, except in general terms (TCBOR SG, LTR
MMC).  Does 4" sound reasonable for something in the
450-900 watt range?

Yes, a 4" dia secondary is well suited for building a
TC that produces 36" sparks.  My secondary plugs into
the base assembly for easy portability.



Thanks to everyone for your help!

-Michael Johnson