Re: eddy current with secondary coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi Chris,

On 5 Oct 2003, at 11:15, Tesla list wrote:

 > Original poster: "chris swinson" <exxos-at-cps-games.co.uk>
 >
 >  > Low-frequency inductances and mutual inductances. Most of the
 >  > formulations that I used assume uniform current in the wires,
 >  > radially and along them.
 >  >
 >  > Skin and proximity effects have some effect on inductances, but
 >  > the most serious deviation from the DC values in this case is
 >  > caused by the capacitances of the coils changing the currents
 >  > along the wires. It's easy to take this into account, if the
 >  > current profiles are known, but this is not implemented in my
 >  > program yet. The program developed by Paul Nicholson (Acmi) can
 >  > take the current profiles into account.
 >  > Eventually I will look at this problem, but I would like to find
 >  > first a good method to calculate the current profiles.
 >  >
 >  > Antonio Carlos M. de Queiroz
 >  >
 >  >
 >
 >
 > Is there a program which will calculate secondary coils with space windings
 > ? and maybe even further do the math to work out various resistance and
 > current effects of litz wire also ?

You don't need computer programs to do trivial first-order calcs. All
you need to know to get a roughly characterized secondary is the
winding height (length), winding diameter, and number of turns. From
that you can derive inductance, capacitance and resonant frequency to
within a few percent using Wheeler and Medhurst's formulas. The
additional capacitance of a terminal placed on top can be measured by
the drop in frequency it causes or, if you have a reasonable amount
of experience, roughly guessed at according to the terminal and coil
sizes. NB - the consideration of spacing the wire doesn't even enter
the mix as long as the spacing is uniform along the coil length.

      For ESR calcs based on wire types and sizes, something else is
indeed required but to produce a running coil, it is unnecessary to
know this.

Malcolm