Re: gdt

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

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

 > Original poster: David Speck <dave-at-davidspeckmd-dot-org>
 >
 > Claude,
 > One way to get a precise turns ratio is to use 5 parallel lengths of
 > wire loosely twisted into a bundle,  and wind your transformer with
 > them. If you designate the wires as A, B, C, D, and E, then let A be
 > your primary, and connect the end of B to the start of C for one
 > secondary, and the end of D to the start of E for the other
 > secondary.
 >
 > Some of the "real" electronics gurus on the list could tell you how
 > many turns you would need.  The optimum number depends  upon the
 > dimensions of the core, the permeability of the material and
 > possibly the operating frequency range.  My bet is that something
 > between ten and 25 turns would be OK, but you may have to try a
 > couple different values.
 >
 > If anyone could post a precise formula, or directions to the same,
 > I'd be interested in seeing that myself.
 >
 > HTH,
 > Dave

Some years ago I developed a straight forward design procedure for
doing this. It would require a bit of time to write up but if there
is any interest, I will take the time and write it up properly and
post it to the list.
      The nub of it is to decide on the maximum flux density you will
allow in the ferrite as this defines the losses you can live with and
determine the applied magnetizing force which then spits out the
minimum number of turns required. There is obviously a bit more to it
than that but it's not rocket science.

Malcolm