Thank you for making me get off my butt and do some analysis (and also
correct some stupid errors).

I would like to correct part of what I said.

"With these conditions, the result is that the stored energy in the gap
(which is what we are really concerned with with regard to force and with
regard to what we can actually observe) rises to a peak (in this case when
the gap and magnet length are equal) and then falls off (which is not what
I expected) - and the internal stored energy in the magnet also does the
same- I will check this but I do note that at B or H =0 the magnet's stored
energy is 0 and the maximum energy point is somewhere in between -in fact a
situation close to that at maximum power transfer in a resistive circuit
appears to exist. "

This is not correct. I was introducing unnecessary complications as well as
some embarrassing mathematical asinities not worthy of a freshman.

In fact with the structure that I have indicated as well as the case of two
magnets facing each other (same thing but 2 of everything except cross
section), the force varies as the inverse of the square of (l+g) where l is
the magnet length and g is the gap.
The relationship delta(W field) =delta(Wmech) hold true (Wfield is the
stored energy in the field and Wmech is the external energy in opening the
gap by some delta(g)) If the gap is opened from 0 to infinity (neglecting
fringing etc) the stored energy and the total work done rises asymptotically
from 0 to a finite value. Results from the mechanical energy change and the
field energy change agree both in sign and magnitude.
Note that the magnet is working in the second quadrant of the B-H curve and
in the region where the permeability of the magnet is essentially muo. This
is the basis for saying that the flux in the gap is nearly constant for
small gaps. In this region, as the gap increases, the change in energy under
the B-H curve is positive (H negative and B going more negative).

The rest of what I said seems OK.

--

Don Kelly d...@shawcross.ca
remove the X to answer

Thanks for the clarification. I had read your earlier post with
interest, even though I didn't respond to it.

Now you are re-opening the basic controversy by saying that
according to your corrected calculation, you believe that the
work done by separating the magnet from the iron can be
found in the field energy.

I think you might be wrong about this. Consider two C-shaped
permanent magnets touching each other, north to south and
south to north. The field energy is totally contained within the
magnetic material, nothing leaking out to the air. And
there is quite a lot of field energy...I think it's significantly
MORE than double the internal field energy of the magnets
taken separately. There certainly seems to be a superposition
effect of one magnet's B-field times the other magnet's H-field.

Now DO SOME WORK by twisting the magnets around so
that they are north-against-north and south-against-south.
Are you saying there is MORE field energy in this configuration?
It's hard to see how that can be, since now, in the vicinity
of the pole faces, one magnet's B-field cancels the other magnet's.
It certainly seems to me that everywhere within the magnets there
is less field energy. As far as the field leaking outside, it's hard
to see how this would make up for wha'ts been lost.

So I don't think you can properly get the work done in these
magnetic situations by tracking the field energy. I do recall
certain situations where you seemed to get the right answer
but when you looked at it carefully, the SIGN was reversed.
So you did work on the magnets and ended up with LESS
field energy than you started out with. Look at, for example,
the gap energy of two C-shaped magnets as you rotate them
from NS-NS to NN-SS orientations. In the first case you have
field lines superposing and adding up, in the second case
you have field lines opposing and cancelling. And yet you have
to do work to get from the first orientation to the second. You
do all that work and you make the field lines go away. Where
is the energy now?

Marty

--------------------------

On Jan 28, 9:24 pm, "Don Kelly" <d...@shaw.ca> wrote:
Thank you for making me get off my butt and do some analysis (and also
correct some stupid errors).

I would like to correct part of what I said.

"With these conditions, the result is that the stored energy in the gap
(which is what we are really concerned with with regard to force and with
regard to what we can actually observe) rises to a peak (in this case
when
the gap and magnet length are equal) and then falls off (which is not
what
I expected) - and the internal stored energy in the magnet also does the
same- I will check this but I do note that at B or H =0 the magnet's
stored
energy is 0 and the maximum energy point is somewhere in between -in fact
a
situation close to that at maximum power transfer in a resistive circuit
appears to exist. "

This is not correct. I was introducing unnecessary complications as well
as
some embarrassing mathematical asinities not worthy of a freshman.

In fact with the structure that I have indicated as well as the case of
two
magnets facing each other (same thing but 2 of everything except cross
section), the force varies as the inverse of the square of (l+g) where l
is
the magnet length and g is the gap.
The relationship delta(W field) =delta(Wmech) hold true (Wfield is the
stored energy in the field and Wmech is the external energy in opening
the
gap by some delta(g)) If the gap is opened from 0 to infinity (neglecting
fringing etc) the stored energy and the total work done rises
asymptotically
from 0 to a finite value. Results from the mechanical energy change and
the
field energy change agree both in sign and magnitude.
Note that the magnet is working in the second quadrant of the B-H curve
and
in the region where the permeability of the magnet is essentially muo.
This
is the basis for saying that the flux in the gap is nearly constant for
small gaps. In this region, as the gap increases, the change in energy
under
the B-H curve is positive (H negative and B going more negative).

The rest of what I said seems OK.

--

Don Kelly d...@shawcross.ca
remove the X to answer

This all comes from application of conservation of energy which, as far as I
know, has passed all tests successfully. If you are applying external work,
you are increasing the stored energy in a permanent magnet system.
Conservation of energy also means no free ride.

Sure there is more stored energy than that because there is energy stored at
B=Bo due to the energy put in to get there in the first quadrant of the B -H
curve-BUT -we can't get at it. We are limited to the second quadrant where
opening the gap increases the stored energy. The maximum stored energy
will be where leakage determines the effective gap- but this is beyond the
limits of the simple model above.
To make a long story shorter- the increase in stored energy is equal to the
external work put in.

(snip)

This all comes from application of conservation of energy which, as far as I
know, has passed all tests successfully. If you are applying external work,
you are increasing the stored energy in a permanent magnet system.
Conservation of energy also means no free ride.

Don Kelly

Sure there is more stored energy than that because there is energy stored
at
B=Bo due to the energy put in to get there in the first quadrant of the
B -H
curve-BUT -we can't get at it. We are limited to the second quadrant
where
opening the gap increases the stored energy. The maximum stored energy
will be where leakage determines the effective gap- but this is beyond
the
limits of the simple model above.
To make a long story shorter- the increase in stored energy is equal to
the
external work put in.

(snip)

This all comes from application of conservation of energy which, as far
as I
know, has passed all tests successfully. If you are applying external
work,
you are increasing the stored energy in a permanent magnet system.
Conservation of energy also means no free ride.

Don Kelly

Hold on. The reason we're having this discussion is because
conservation
of energy seems to give the wrong answer. Do you remember that guy
Rudy who posted this question in the first place? He wanted someone
to analyze this with thermodynamics. Why? Maybe because you have
to look at the entropy of the magnet to get the right answer. Don, you
are ignoring some very clear problems with the conservation of energy.
It DOESN'T give the right answer, and sometimes when it SEEMS to,
you look more closely and you find the sign is wrong. This needs to
be explained.
------

If you are not convinced by the very clear example I gave previously,
then consider the rotary magnet configuration of a multipole motor.
The rotor and stator each have N-S-N-S-N-S...alternating poles.
When they are lined up north-versus-north, the field vectors CANCEL
and there is NO stored magnetic energy. When you allow it to rotate,
so north faces southy, the field vectors re-inforce and there is LOTS
of
field energy. How do you explain this by conservation of energy?
---------

It doesn't help if you look at the internal energy of the iron, Once
again,
in the north-versus-north position, the rotor field goes against the
stator
field and vice versa, so the energy is LESS than in the north-south
orientation.
---------

The only escape I can see at the moment is to consider that perhaps
in the north-south case, the ENTROPY of the magnet is much lower,
and that the work done in pushing the north poles into alignment goes
into T-deltaS work? That would have all kinds of implications: for
example,
every time your automotive ignition coil made a spark, the iron would
cool down slightly as the magnetic domains randomized themselves.
Is that how it really works?
-------

------
I see no sign problems. Also please note that conservation of energy is, in
fact, the first law of thermodynamics.

------
I see no sign problems. Also please note that conservation of energy is,
in
fact, the first law of thermodynamics.

There is a problem. If the world were as you describe it,
then there would be more magnetic energy in a pair
of counter-wound magnets placed north-versus-north
than in the same pair of magnets lined up "properly".
------------

Then why don't the people who make ignition coils
wind them that way, with two counter-acting coils on
the same magnetic core?
---

For that matter, if there is more energy in a magnetic loop
with a large air gap, why don't the people who make ignition
coils wind them on a core with a large gap? I haven't taken
one apart recently, but I'm guessing the core is a closed
rectangular toroidal form. Do you doubt it?
-------------

Would it be better for a core to flap its permeability between soft
and hard over the workloop?

----------------

"Autymn D. C." <lysde...@sbcglobal.net> wrote in messagenews:1170830657.363756.79430@s48g2000cws.googlegroups.com...
Would it be better for a core to flap its permeability between soft
and hard over the workloop?
Please clarify this. Do you mean between high and low permeability? If so,
in most cases, that would result in inefficient use of the iron-i.e.
driving the core into saturation. If you mean a core with areas of high and
low coercive force, that is done in a hysteresis synchronous motor.

On Feb 7, 2:49 pm, "Don Kelly" <d...@shaw.ca> wrote:
"Autymn D. C." <lysde...@sbcglobal.net> wrote in
messagenews:1170830657.363756.79430@s48g2000cws.googlegroups.com...
Would it be better for a core to flap its permeability between soft
and hard over the workloop?
Please clarify this. Do you mean between high and low permeability? If
so,
in most cases, that would result in inefficient use of the iron-i.e.
driving the core into saturation. If you mean a core with areas of high
and
low coercive force, that is done in a hysteresis synchronous motor.

The latter--if I wantd a core to act as a kimera between a magnetic
tank and a capacitant-inductor. I guess I mean a magnetic flux
capacitor...
-----------------

----------------------------
"Autymn D. C." <lysdexia@sbcglobal.net> wrote in message
news:1170928944.347574.252140@m58g2000cwm.googlegroups.com...
On Feb 7, 2:49 pm, "Don Kelly" <d...@shaw.ca> wrote:
"Autymn D. C." <lysde...@sbcglobal.net> wrote in
messagenews:1170830657.363756.79430@s48g2000cws.googlegroups.com...
Would it be better for a core to flap its permeability between soft
and hard over the workloop?
Please clarify this. Do you mean between high and low permeability? If
so,
in most cases, that would result in inefficient use of the iron-i.e.
driving the core into saturation. If you mean a core with areas of high
and
low coercive force, that is done in a hysteresis synchronous motor.

The latter--if I wantd a core to act as a kimera between a magnetic
tank and a capacitant-inductor. I guess I mean a magnetic flux
capacitor...
-----------------
In answer to your question, if I want the coercive force to change, it would
be necessary to change the material in the magnetic loop. This presents
certain problems. It does occur in the hysteresis motor at speeds other
than synchronous in that the stator field moves with respect to the rotor
which has two different materials. You won't get one size fits all material.
So - No -if the core is stationary. with respect to the field source.

As for the rest:
Kimera?
magnetic tank?
capacitant inductor?
magnetic flux capacitor?
Sorry, The above terms make no sense to me. They appear to be a hodgepodge
of contradictory terms. Please clarify what you mean.

Do you mean something that can be controlled to appear either capacitive or
inductive? If so there are devices that can do this. Saturable reactors in
parallel with capacitors will do this. These donot involve a change in
coercive force but do involve permeability changes.
If you mean an inductor that acts as a capacitor or a capacitor that acts as
an inductor- the answer is --forget it.
--

Don Kelly dhky@shawcross.ca
remove the X to answer

Do you mean something that can be controlled to appear either capacitive or
inductive? If so there are devices that can do this. Saturable reactors in
parallel with capacitors will do this. These donot involve a change in
coercive force but do involve permeability changes.

If you mean an inductor that acts as a capacitor or a capacitor that acts as
an inductor- the answer is --forget it.

Don Kelly <dhky@shaw.ca> wrote:
----------------------------
"Autymn D. C." <lysdexia@sbcglobal.net> wrote in message
news:1170928944.347574.252140@m58g2000cwm.googlegroups.com...
On Feb 7, 2:49 pm, "Don Kelly" <d...@shaw.ca> wrote:
"Autymn D. C." <lysde...@sbcglobal.net> wrote in
messagenews:1170830657.363756.79430@s48g2000cws.googlegroups.com...
Would it be better for a core to flap its permeability between soft
and hard over the workloop?
Please clarify this. Do you mean between high and low permeability?
If
so,
in most cases, that would result in inefficient use of the iron-i.e.
driving the core into saturation. If you mean a core with areas of
high
and
low coercive force, that is done in a hysteresis synchronous motor.

The latter--if I wantd a core to act as a kimera between a magnetic
tank and a capacitant-inductor. I guess I mean a magnetic flux
capacitor...
-----------------
In answer to your question, if I want the coercive force to change, it
would
be necessary to change the material in the magnetic loop. This presents
certain problems. It does occur in the hysteresis motor at speeds other
than synchronous in that the stator field moves with respect to the rotor
which has two different materials. You won't get one size fits all
material.
So - No -if the core is stationary. with respect to the field source.

As for the rest:
Kimera?
magnetic tank?
capacitant inductor?
magnetic flux capacitor?
Sorry, The above terms make no sense to me. They appear to be a
hodgepodge
of contradictory terms. Please clarify what you mean.

Do you mean something that can be controlled to appear either capacitive
or
inductive? If so there are devices that can do this. Saturable reactors
in
parallel with capacitors will do this. These donot involve a change in
coercive force but do involve permeability changes.
If you mean an inductor that acts as a capacitor or a capacitor that acts
as
an inductor- the answer is --forget it.
--

Don Kelly dhky@shawcross.ca
remove the X to answer

Gyrator.

Though it is electronic trickery that makes it work.

--
Jim Pennino

Remove .spam.sux to reply.