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

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.
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.
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.
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?

"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.

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.

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.

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.
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

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

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.

John Larkin wrote:

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

Thanks for more a more elegant explaination (than the one i just
posted before seeing yours).

"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

"Robert Baer" wrote in message
ink.net...
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 there 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.

I don't know if you looked at the attached picture, I think it shows
what I'm trying to explain. But, maybe I should have said, grind a 1/4"
wide notch deep enough for two layers of wire on the top and bottom
side of the toroid. And if I need more turns I'll do the same thing 180*
opposite the first notch.



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.

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

"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

On Thu, 19 Apr 2007 08:31:07 -0700, John Larkin
wrote:

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.

The toroid is not gapped, it is placed in a pot core gap.

A ferrite toroid is easily saturated at low power levels.

RL

On Thu, 19 Apr 2007 19:31:45 -0500, "amdx" wrote:

snip

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.

Google 'saturable reactor' or 'magnetic amplifier'.

Your proposed construction isn't out of the question for a
small-signal circuit.

The most common form is that used in conventional television
where two out of phase windings on the outer legs of an E-core are
used to control the permeability of the signal winding present on the
center leg.

The next most common is the two toroid structure, where control
windings are wound on two separate toroids; these are sandwiched and
used as a single toroid structure for the main signal or power
winding.

RL

On Fri, 20 Apr 2007 21:21:57 -0400, legg wrote:

On Thu, 19 Apr 2007 08:31:07 -0700, John Larkin
wrote:

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.

The toroid is not gapped, it is placed in a pot core gap.

The illustration sort of looked like it was. I suppose it was just
necked down, which is a partial gap. Still, he won't get a lot of
ampere-turns in a structure like that, not without frying the wire.

John

"John Larkin" wrote in message
...
On Fri, 20 Apr 2007 21:21:57 -0400, legg wrote:

On Thu, 19 Apr 2007 08:31:07 -0700, John Larkin
wrote:

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.

The toroid is not gapped, it is placed in a pot core gap.

The illustration sort of looked like it was. I suppose it was just
necked down, which is a partial gap. Still, he won't get a lot of
ampere-turns in a structure like that, not without frying the wire.

John

"John Larkin" wrote in message
...
On Fri, 20 Apr 2007 21:21:57 -0400, legg wrote:

On Thu, 19 Apr 2007 08:31:07 -0700, John Larkin
wrote:

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.

The toroid is not gapped, it is placed in a pot core gap.

The illustration sort of looked like it was. I suppose it was just
necked down, which is a partial gap. Still, he won't get a lot of
ampere-turns in a structure like that, not without frying the wire.

John


Yes, I now see the confusion, The toroid is necked down, it is not gapped.
Thanks for straightening that out.
Mike

On Sat, 21 Apr 2007 05:49:50 -0500, "amdx" wrote:

snip

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

The toroid is not gapped, it is placed in a pot core gap.

The illustration sort of looked like it was. I suppose it was just
necked down, which is a partial gap. Still, he won't get a lot of
ampere-turns in a structure like that, not without frying the wire.

John


Yes, I now see the confusion, The toroid is necked down, it is not gapped.

If the toroid is not completely enclosed in the control winding, you'l
get unpredictable results.

A necked toroid (as drawn) that actually made physical contact with
the potcore, would share flux with the pot core body, reducing the
ability of the coil to saturate the ferrite in the area of contact.

Only the relatively small volume enclosed by the winding could be
garanteed to saturate.

RL

I have been following this thread and just picked this point
to jump in.

I also have pondered how a core and coil structure might be
made that would allow the flux in one section to be
saturated without coupling the signal from the unsaturated
part into the saturating coil.

I think your toroid in pot core gap structure would work
best with the entire surface of the toroid wound with fine
wire (two layers, around and back to the starting point, to
avoid a 1 turn "secondary" of the pot core "primary").

This structure does provide a small gap (at least two toroid
winding wire diameters) in the pot core flux path, but a
variable gap, none the less.

The problem with your notched toroid structure, is that
there is a flux path across the notches, through the pot
core material that detours flux that would otherwise go
around the toroid, so you end up only saturating the toroid
under the windings, not all the way around.

You could also just wind the assembled pot core toroidally,
so that the toroid winding is used to saturate the entire
hollow center leg of the pot core. This would work best
with a pot core that includes a couple (or more) slots along
the outside circumference to bring the core windings out
through, so that only the center, hollow post is saturated.