"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.


In the ideal case the fringe effects are usually ignored. Atleast every book
I've read about inductance supposes the fringe effects can be ignored.
Remember, we are talking about the inductive effects on heating those ends
and not the inductance itself.

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.

In all causes if the the ends are relatively symmetric then both should heat
up equally. Also the fringe effects tend to reduce the heat on the ends and
not increase it. Also all the effects you describe should heat the central
windings more than the outside and have little to do with the end turn
amount. Again, In all cases it would be symmetric unless the core or
windings themselfs were wound in some weird way. 99.99999% of all inductors
are wound to be symmetric.

So if there is some effect that is due to the reasons you describe then it
must be because they let a 2 year old create the winding.

Now, you'll have to excuse me if I make some assumptions about what is going
on. When he says inductor I think of basically something that looks like an
inductor and acts like one. So if he did something non-standard then he
should include that information.

I cannot totally exclude some physical reason why such a thing could happen
because I don't know all the possibities. Given the assumption that what
they created was very much inductor like no one has presented any reason why
only one side would heat up and the rest of the coil would be fine that is
due to the coil/core.

The most likely effect is that the connection on that one end was bad or was
shorting out. This is the best guess given the little amount of information
that was provided.

Since he said the same result was produced independently then this possibly
suggests something else but the same mistake could have been made twice.

It would be quite easy to create a partially laminated core that was not
laminated near one end. The core would heat up due to eddy currents which
would heat up the 1/2 turn first. Who the hell would use such a core? Such
behavior is to be expected when someone doesn't know what they are doing.