On Wed, 19 Jan 2011 09:39:14 -0500, Bob Engelhardt
wrote:

wrote:
If I recall correctly when one designs a transformer, you calculate
what the ET product is. ...
snip
So the flux ( B ) depends on the voltage and frequency. And using the
same line frequency and the voltage at 240 volts RMS ( much less than
the usual 2000 volts on the secondary, you should not have to worry
about saturation. ( this assumes you are using AC voltage.).

Thanks, that helps!

I've been thinking about those 2000 volts. If that's the normal voltage
on this coil, it's probably going to take close to that to saturate the
core. I mean, wouldn't they design for the core to be close to
saturation, to minimize the core size needed?

My interest in saturation is 2 fold: I don't want to run beyond
saturation 'cause of the extra heat, and at saturation is where the
maximum pull will be.

Now, about ACC. To use as an electromagnet, I have full-wave
rectification, unfiltered. Although the coil's inductance will do some
smoothing (I wish my scope was working). My intuition is that the DC
component of the current will be determined by the coil resistance and
that will produce flux proportional to the number of coil turns. So,
the question is whether the DC current will saturate it before 240v. Or
be too high for the coil's wire guage.

But the bottom line is that I'm going to be using 240v max (full wave)
and as long as it isn't saturated then, I'll be getting the maximum pull
available.

Thanks,
Bob

You're right, DC current will be determined by coil resistance and
applied voltage, and flux will be proportional to current and # of
turns.

Focus on keeping the current to a level that won't burn out the
winding. Don't worry about saturation in a DC electromagnet. Having
it saturate is not a problem. Saturation is a big problem in a
transformer, but not in an electromagnet.

It's a bit surprising that, for given core cross section and winding
window area, the max flux possible with a copper winding is
independent of wire size. Voltage and current change, of course, but
Bmax doesn't for given current density in the copper.

The attraction force you get will be B^2*A / 2*muzero where B is flux
density, A is area, muzero is 4*pi*10E-7 newton/amp^2. Flux density
will depend on the total magnetic circuit including whatever is being
attracted.