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Re: Pancake Primary (fwd)
---------- Forwarded message ----------
Date: Sat, 14 Feb 1998 23:34:03 -0800
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Pancake Primary (fwd)
Tesla List wrote:
>
> ---------- Forwarded message ----------
> Date: Sat, 14 Feb 1998 18:31:05 -0500 (EST)
> From: SBJohnston-at-aol-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Pancake Primary
>
> Many folks have recommended a flat pancake-style primary coil instead of my
> current vertical air solenoid coil.
> I remembered I have a big roll of new 1" copper strap that could be used to
> make a nice flat primary, so I guess I should give it a try.
>
> I wonder how to mount such a coil (Hmmm... maybe an "X" of wooden 1"x1"
> strips with slots cut partway thru?) and how far apart to space the turns?
>
> Also... Can anyone help me out with the equation for calculating the
> inductance of a flat spiral coil of this sort? Thanks!
>
> Steve Johnston
>
> sbjohnston-at-aol-dot-com
Steve,
You may actually get better results using copper tubing, since the round
profile is less conducive to generating corona and flashovers. In any
event, and approximation of the inductance of a flat primary at turn "N"
can be found for either:
Center
Line
|
O 0 0 0 0 0 0 0 | 0 0 0 0 0 0 0 O
|
|<----------------->|<--->|
a b
a = outer radius at turn "N" (inches)
b = inner radius (inches)
N = turn number
R = Ave. Radius = (a+b)/2
W = coil width at turn "N" = a-b
L = (R^2 )*(N^2)/(8*R + 11*W) in MicroHenries
Generally, the innermost radius (a) should provide at least 1.5" of
clearance to the secondary coil to prevent primary:secondary flashovers.
You should also have no less than 1/4" of air space between adjacent
primary turns, and more (3/8" - 1/2") if you're running at higher power
levels or with few primary turns.
Safe coilin' to you!
-- Bert --