Winding a strong electromagnet

[Xaverius]

I STILL can't get me brain around this - thinking I'm brain damaged! 

I have a magnet attached to the end of an electromagnet (EM) with a steel core and pulse the EM with just enough juice to get the magnet to drop off.

Which will require less energy input to get it to drop off?

1) a high permeability core
or
2) a low permeability core

(1-A) the magnet is very strongly attached to the high permeability core and almost all the domains of the core are aligned.  This will require a large input of energy to negate the attraction.  BUT, will the high permeability core more readily 'accept' the flux from the EM pulse meaning it will actually require LESS?

(2-A)  the magnet is attached, but not quite as much as a much smaller % of the domains of the core are aligned, thus less energy input to the EM to get it to drop.  BUT, will the core also be less 'accepting' to the EM pulse so it will require more input?

Or a small size core with a relatively large/strong magnet is going to fully saturate the core, so the high permeability core will require less.
But if the core is large with a relatively small/weak magnet this changes things?

Or what and why?

Tx

For drop off, a high permeability core should require less power input.  The high u core causes a greater ATTRACTION force between it and the PM.  However, the high u core uses a unit of power to produce a greater REPULSION force.

The REPULSION force must be equal to the ATTRACTION force in order to repel the PM.  If the REPULSION is too weak(such as with a low u core) for a unit of power, then the PM will still be ATTRACTED to the core.  Ex.  PM has 2 units of force, core has 1 unit of force, total attraction 3 units.  If PM has 2 units of attraction and core 1 unit of repulsion you still have 1 unit of attraction, 2+-1=1.  Therefore you would need 2 units of power to produce more force(negative) for the low u core to repel the PM.

BTW, the PM will not just drop off, magnets work on an all or nothing basis, the PM and core will repel with rapid speed and distance between them.

Hope this makes sense, the high u core would use less power.

[tropes]

For drop off, a high permeability core should require less power input.  The high u core causes a greater ATTRACTION force between it and the PM.  However, the high u core uses a unit of power to produce a greater REPULSION force.

The REPULSION force must be equal to the ATTRACTION force in order to repel the PM.  If the REPULSION is too weak(such as with a low u core) for a unit of power, then the PM will still be ATTRACTED to the core.  Ex.  PM has 2 units of force, core has 1 unit of force, total attraction 3 units.  If PM has 2 units of attraction and core 1 unit of repulsion you still have 1 unit of attraction, 2+-1=1.  Therefore you would need 2 units of power to produce more force(negative) for the low u core to repel the PM.

BTW, the PM will not just drop off, magnets work on an all or nothing basis, the PM and core will repel with rapid speed and distance between them.

Hope this makes sense, the high u core would use less power.

Before building my 4th Sotropa Motor (3/4' neo. magnet pistons), I used this simple apparatus to test the coil, core and voltage requirements:  http://www.youtube.com/watch?v=pNWAlj_lBUk
In my last motor I used an iron pipe as a core. The core diameter is half the magnet diameter and the coil diameter is equal to the magnet diameter. I used 22 gauge wire and added voltage until the coil heated. Removing the BEMF allowed the coil to run cooler. I found that a solid core with no clearance between the core and magnet was impossible to to separate regardless of how much voltage was applied.
Hope this is of some value to those builders.
Tropes

[capthook]

Found this core material study online.

As proper annealing is expensive and difficult to source, especially in small quantitites, the conclusion was that unannealed 'Magnet Iron' was of relative quality compared to expensive annealed Hiperco 50A.

"Magnet iron is recommended for unannealed use"

[Ergo]

All of your calculations and drawings is not valid in your pursuit of
making the strongest electromagnet possible.
The permeability only correlates to a closed magnetc circuit.
You will not see any dfference in magnetic strength when using
advanced core material in an open frame electromagnet.
The tiniest airgap present will deteriorate the properties of the
high efficiency core material. So no gain of strength in this case.

But there is still another advantage that not many people know about.
The only really useful advantage of using high tech core material.
Simply the Hysteresis effect.
Hysteresis is the loss on each charge/discharge of the electromagnet.
It takes a certain amount of energy to energise the coil.
But you never get the same amount back as EMF when shut down.
This loss can be minimised by using Hi Tech core material.
When minimising the hysteresis you get rid of the core heating and
you can then run the electromagnet harder without overheating.
But this only matters in a repetitive pulsed state. In static mode
or unfrequently pulsing you can just as well use a regular iron core.

[capthook]

The permeability only correlates to a closed magnetc circuit.
You will not see any dfference in magnetic strength when using
advanced core material in an open frame electromagnet.
The tiniest airgap present will deteriorate the properties of the
high efficiency core material. So no gain of strength in this case.

Do you have any supporting evidence/links?
It would seem contrary to any information I've seen.
Either the domains align more easily due to the molecular structure of the material (high permeability) or they don't (low permeability).  How would the airgap be revelant to this?

- - -
Xaverius-
I did some testing on the 2-strand winding idea to reduce the resistance of the coil and thus increase efficiency/flux.
While this idea may be of benefit when additional power is available, I find it not to be so with a fixed power input.

Testing two identical coils with the only difference being a 1 wire winding vs. a 2 wire winding and a power supply of a 4700 uF capacitor charged to 12V:
The 1 wire was on average 17% more efficient(provided more flux) over varying test conditions/airgaps. 
- - -
Some further updates on materials/annealing:

I've found min. charges of around $250 for hydrogen annealing at 1600F for 2 hours with a 4 hour 100F cooling cycle to be about the norm.  1 provider offered to 'piggyback' on a another order providing time was not an issue (maybe 2 weeks) for $150.

Pure iron (99.95%) @ $90 per inch (OUCH!! $$$)
Iron rod (99.6%) @ $95 per ft.

CMI-C magnet iron 4' for $100 to $250 depending on the providers min. order.