"whit3rd" wrote in message
...
On Aug 27, 10:31 am, "Jeff Johnson" wrote:

The theory of ideal inductors does not give any reason why a 1/2 turn
should
at all be important.

Oh, yes, it DOES give a reason. A pot core (or E cores) has a pair of
return
flux arms flanking the central element, and a '1/2 turn' winding
imbalances
those return fluxes.

That means the 3-d flux inside the core is very different in the
two cases, and if one return arm saturates, that flux distribution
alters
considerably during the cycle. That causes (1) the material to heat
due to remagnetization in an asymmetric way, (2) the forces of the
pole pieces to modulate as the field builds. The first effect (caused
by material hysteresis) might have been expected. The second
effect, though, will cause ultrasonic excitation of the core, maybe
creating cracks by mechanical stress.

Some may find interest in this.
A turn around an outside leg of an E-core is called a half-turn because it
encloses only one-half of the cross-sectional area of a turn around the
center leg. It is well known that a half-turn in a secondary winding of a
power transformer greatly increases the leakage inductance between windings,
thus causing an adverse effect on cross-regulation. However, the increased
leakage inductance of a half-turn can be very beneficial in tapped inductors
for boost circuits and in coupled output chokes. This paper explains some of
these little-known applications of a half-turn. The theory and formulae for
prediction of leakage inductance added by such a half-turn are presented
http://ieeexplore.ieee.org/Xplore/lo...hDecision=-203