On Sat, 22 Sep 2007 15:10:18 -0600, Joe Pfeiffer
wrote:

writes:

On Sat, 22 Sep 2007 10:17:21 -0600, Joe Pfeiffer
wrote:

That's a really nice piece of work!

I'd have to dig out my freshman physics book to be sure, but I expect
the reason filling the space in the transformer is good is to have as
much magnetic field as possible in the conductor, giving as much
current (ie efficiency) as possible.

Optimum economic use of the total weight of copper is when
the volume of the copper in the secondary is about equal the
copper volume in the primary because this equalises the primary
and secondary copper losses. It's a very flat optimum and various
second order variables shift it a bit either way.

That makes sense -- my intuition is that this implies that if the goal
isn't economic optimum but rather maximum current then filling the
volume accomplishes it...

When you've removed both the high voltage winding and the
magnetic shunt from a microwave oven transformer the winding
space left is a lot more than that occupied by the primary, so
it's possible to install a much larger volume secondary.

If you're using welding cable most of the possible output
is achieved once the copper volume has exceeded the primary
copper volume. If you're using Aluminium aim for more at least
50% more volume because of the higher resistivity.

Volume or area (of course, in this application increasing the volume
does increase the area)?


More secondary conductor always gets a bit more output but
it's a diminishing rate of return.

In trying to keep the explanation simple I was a bit
cavalier in the use of the term "volume". Volume is the correct
yardstick if (as is usually the case) the overall physical shape
and average turn length is pretty similar for both primary and
secondary.

A more accurate yardstick is the comparative fraction of
the window area occupied by the total cross sections of the
primary and secondary conductors.

However even this mouthful gets into trouble if the
primary and secondary average turn lengths are widely different!

Jim