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Re: K Factor & Mutual Inductance
Subject:
Re: K Factor & Mutual Inductance
Date:
Sat, 12 Apr 1997 00:35:00 -0500 (EST)
From:
Benson_Barry%PAX5-at-mr.nawcad.navy.mil
To:
tesla-at-pupman-dot-com
Hi John, All,
The formula was in an RF xcel spreadsheet design book.
L = coil inductance
C = toroid capacitance = coil self capacitance X 2
for my present calculations.
R = RF wire resistance with skin effect, proximity effect,
and other nonlinears fudged in.
I am using R ~= 3.1 X wire DC resistance for my
present calculations.
sqrt(L / C) is called the surge impedance.
If you design a Marx generator so that the load impedance
is equal to the surge impedance of the Marx then you get
maximum energy transfer, no nasty reflections back into
the Marx, and a good spark.
With the above L, C, and R I'm getting some Tesla coil
with toroid surge impedances of around 50 ohms, coil
wire RF resistances between 200 and 300 ohms, and Qs
around 100 max. The formulas in my spreadsheet
aren't accurate enough to say anything about this yet.
Barry
>
>
>Hi John, All,
>Have you ever tried the formula Q = sqrt( L / C ) / R.
>
>Barry
>
> ----------------------------------------------------
Barry -
I have never seen the above Q factor equation before. What would you
use
for R? In the usual equation Q = X/R where X = 6.283 F L the R is
an
effective resistance, not DC or AC. The only way to find the R is to
use a
value for a typical Q and X and solve the equation for R. The Q factor
like
the K factor is easily found by tests after the TC is built, however, at
the
design stage these two factors are difficult to determine.
The basic nature of Q for Tesla coils has to do with the energy stored
in
the field of the coil and the energy dissipated. The Q factor also
involves
resonant rise in voltage and other electrical effects. It is also
interesting that Q involves other phenonmena such as in the swing of a
pendulum and in horological science ( measuring time).
John Couture