On Tue, 20 Jul 2004 02:12:47 -0500, "Tim Williams"
wrote:

"Don Foreman" wrote in message
.. .
A given sized core can only handle so many VA at
given frequency (60 Hz)...

No, it can handle a certain number of turns per volt (which of course has a
factor of frequency, yadda yadda, but we're at 50/60Hz only so forget about
it). Current depends on the wire. That's why you can short a transformer
and get the windings smokin'...

Well, golly, do you suppose I've been designing transformers wrong
for 35 years?

Given 60 Hz, and given max flux density determined by the core
material , volts per turn (or turns per volt if you prefer) are a fn
of cross sectional area enclosed by the winding. However, for more
VA (at given voltage) you need to use larger wire for those turns.
This dictates more "window" area so the overall dimensions
(envelope), volume and weight of the core must be larger to make a
larger window.