"Tim Williams" wrote in message
...
"Jeff Johnson" wrote in message
...
big ****in snip
The reason is that the current through the wire will almost be surely the
same through out all points along the wire.

Well, no:
http://en.wikipedia.org/wiki/Proximi...romagnetism%29

the current density varies strongly, especially if the wire is thick
(curiously, it was never stated what size wire is in question, nor what
type; 600kHz suggests fine stranded litz!).


Again it has been 10 years, but I think the coil in question had something
like 4-24 gauge wires in parallel, maybe 28 gauge.

Wire near the gap (which is usually placed in the center, right underneath
the winding) experiences fringing fields, which dramatically increases
losses.

Yes, we learned to space our wire away from the gap, after finding burned
wire and melted bobbins in the center where the gap was.

That precisely means that the heat generated per unit length will be the
same.

Eddy currents in the center of the coil are much stronger than at the
ends, so the center of a solenoid heats up much more strongly.

The uncooled coil in this video demonstrates proximity effect:
http://www.youtube.com/watch?v=nY66rBJvbpY
See the connections are clean and coppery, but the coil has seen better
days. You can't really tell if the center turns are hotter; they probably
are by a little bit.


Of course Kirchoff is harder to fool, obviously the total current flowing
along the wire is the current flowing along the wire period. Unless
there's a short, which supposedly was inspected as to have none.


None of these are an "end" effect. The only possible explanation is a
short, or else, "look harder". It's plainly obvious that the cause is NOT
"an additional half turn". It is only a coincidence that this symptom
showed up between turns 4 and 5.

Tim

And some people don't believe in DDWFTTW! :-)
But thanks, MikeK