amdx wrote:
"Robert Baer" wrote in message
ink.net...

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





Please forgive me for a few stupid questions.

1) Why notched? Wind the torid in the standard fashion.


When the potcore is put together it will be a tight fit between the toroid
and
the center of the potcore, no room for a layer of wire, so a notch to make
room
for the wire.
....and??? where does the wire go? if you wrap wire around the toroid as
mentioned in #2, the notch is not useful and the wire makes for a gap on
the "top" and "bottom" of the toroid.



2) Now that there s wire on the toroid, guess what? You hav a gap in the
pot core due to that wire on the toroid.


No, if I notch the toroid three will be continuous ferrite where the
potcore
gap was.
I ask again, where does that wire go? What do you propose - make a
1-turn loop and slip it in that gap? Makes for very lousy coupling to
the toroid if the maximum loop height is that of the toroid.



3) Just for grins, say that wire is of zero dimensions but that one can
run enough current to saturate the toroid. Notice the toroid has a hole in
the center, which will significantly reduce the cross-sectional area in
the center, and thus reduce the Al.


The potcore already has a hole in it! Some potcores with a gap have
an Asu L of about 100 without a gap it is many thousands (10 to 12)
Even if the cross sectional area is reduce significantly say a factor of 10,
I'm still looking at an AsubL of 1000 ungapped vs. 100 gapped.
Then you are in business with the pot core as-is; see #4.



4) Why not take an un-gapped pot core that has a (small) hole in the
center, and run wire thru the center, then use that winding to saturate
the pot core directly?


I'll need to think about that. Although if I'm going to saturate the
larger
potcore, I could just put an extra winding on the bobbin and run the dc on
that.
Bad idea; what you would be adding is an AC "shorted" winding.
In magnetic amplifiers and saturable reactors, is two transformers,
and the "DC" control windings are connected in series opposing to cancal
the AC; each "DC" winding can saturate its respective core.

As an end result I would like to put ac on the toroid winding and try it as
a
magnetic mixer.
Thanks for the thoughts,
Mike



Another way is to super-impose the DC control current on top of the
AC input current.