"John Larkin" wrote in message
...
On Thu, 19 Apr 2007 14:38:58 -0500, "amdx" wrote:


"John Larkin" wrote in
message
. ..
On Wed, 18 Apr 2007 12:26:09 -0500, "amdx" wrote:

Hi,
Does the orientation of flux affect the saturation?

Please see attached picture at ABSE.
Subject: Variable Inductor Help
My thought is to build a variable inductor by installing a toroid in the
gap
of a potcore. The potcore would then have near normal ungapped
inductance.
However when the toroid is saturated (by turns installed on the toroid)
it
would be invisible and act like a gap. Hopefully this effect could be
modulated by the amount of current through the turns on the toroid.The
problem I have is the orientation of the flux, the potcore center flux
is
vertical and the toroid is horizontal. Any thoughts?

Mike



It'd guess that it would be hard to get that tiny winding to saturate
the gapped toroid, and cooling would be nasty.

How about this:

Wind two separate pot cores #1 and #2, each with two windings A and B.

Connect windings A1 and A2 in series, and also connect B1 and B2 in
series but opposite phasing. Use the A circuit for your AC signal, and
run DC current through the B circuit. Current in B will saturate both
cores, but signal in A will not couple into the B circuit because of
the phase difference.

John

Hi John,
That may well work, but I wanted a different material as the saturating
piece. Hopeing to find a material easy to saturate.
Mike


You can saturate a section of a toroid by exposing it to a
perpendictular magnetic field, as say from a second toroid with a gap.
Or vice versa.

Or wind three windings on one toroid: one normal one, and then two
more, bunched one on each side. Phase the two side windings in series
"wrong" so they don't couple to the signal winding. DC in the side
windings creates a field that completes through air but still
modulates permeability.

Hey, you could wind a control solenoid on the outside of a pot core!

Or pass a longish ferrite rod through the mounting hole of a pot core,
partly shunting the gap. Add external windings to the rod to saturate
it. That would satisfy your "different material" spec.

Why do you want a variable inductor?

John

Hi John,
I have no compelling reason to build a variable inductor. It's just a
curiosity.
If the potcore/toroid idea was feasible, I might try using it as a magnetic
mixer
for a radio front end.
Maybe a better question would be; What's the best geometry to bring the
core
of one winding into saturation with the flux from seperate winding.
Mike