Quote from: capthook on March 11, 2009, 11:27:37 AM
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?

Believe it or not but I have studied magnetics for some time now and I can
tell you that I have tested all kind of alloys in a small electromagnet when
trying to optimise its strength.
I have a gauss meter and no matter what I tried I always got the same end
face flux at the same input current.
The fine alloys, (mu metall, MPP, Sendust, Hi Perm oriented Steel) didn't
give any increase in end face flux. I phoned one of the companies and talked
to an engineer on the matter and he told me that any air gap will detoriate
the performance. He also told me about the importance of hysteresis and
why high tech alloys are so good at this compared to solid structures.
He gave me a hint, if I wanted to have an electromagnet that consumed less
current I had to make sure it was bent into a C and the open gap should be
placed tightly against a solid iron return path thick enough to carry all the flux.
In this scenario I would see a drop in current in reaching high flux levels.
But using a Solenoid shape was not an option. The air gap is simply huge.

I have searched internet for a long time but there is no information on this subject.
Either it's burried deep in some heavy science thesis but I believe myself the lack
of infomation is due to lack of interest in this matter. Any involved engineer find
this obvious and there is no literature written on how to optimise a hopeless case.

Edit: I found a new link today. It might provide you with answers but it costs money.
http://www.coursework.info/AS_and_A_Level/Physics/Fields___Forces/_What_effects_the_strength_of_an_electro_L68298.html

Some interesting information on series vs. parallel windings of an electromagnet.

Conclusion: series (or 1 wire) produces greater or equal magnetism vs. parallel (or multiple wires) windings.

"With a power supply configured as a current source, by setting the current and leaving the voltage free to take any value, the nail's magnetism was lower under parallel connection of the coils."
With a variable current supply, the nail's magnetism was equivalent under both series and parallel.

An interesting .pdf is attached.  The author investigates the early work done on parallel vs. series windings electromagnets.

Static testing does not give a complete picture. Two things I have found that reduce the amount of current needed to produce an electomagnet. Both involve movement.
1.) As the magnetic piston moves toward the face of the coil, an electric current is induced in the wire. The current induced in the coil wire by the magnet will be of a polarity that repels the magnet. The magnets use the current induced to make the coil core repel the magnetic pistons.

2.) Utilizing CEMF is a method of lowering the overall power consumption required as it collects stored energy from the coils between pulses, and dumps it into a capacitor.

Tropes

This is why the core material doesn't matter in a solenoid shaped electromagnet regarding flux levels.
It's simply due to the extremely large airgap between the poles and this translates into strong reluctance
in getting magnetised by the applied magnetizing force from the coil.
The reluctance is so strong that it doesn't matter how "easy" the core material is.
The force needed to overcome the large airgap is many times greater than the "magnetizing properties".
The reluctance can only be minimised by decreasing the airgap. And the easiest way is to bend the solenoid
shape into a C where the gap is kept as narrow as possible. And the best performance is obtained when
the C-shape is closed into a toroid shape. This is very easy to magnetise but useless as an electromagnet.

Sorry guys. There is no shortcuts in making a strong electromagnet by using exotic core materials.
But in a pulsed state, preferably at 50Hz or higher, the BEMF at turn off can be recycled at much higher
efficiency than using a regular solid iron core. This is the true benefit of using exotic core materials.

Ergo is completely correct - once you get a decent core (more than 200-500 permeability rating), the impact of getting higher permeability material is somewhat futile.

The reason why parallel coils are useless is because you end up with identical amp turns/amperage.  If you have a power supply that can handle high amperage, it would be nice for keeping voltage low, but would have zero impact upon wattage used to produce the gauss.  Actually, it would probably be more expensive, in wattage terms, because there will be a small amount of additional resistance created by the leads for each of the separate coils (relatively inconsequential though).

For creating a stronger electromagnet, wrapping your core partially around your magnet will have a much higher impact (think of a putting your electromagnet in a steel can with one side removed - the outside of the steel can would turn into your opposite pole).  Your typical industrial magnets have the can completely around so that both poles are on the same side, creating a magnet that is 3-4 times as strong (if not stronger) with the same number of amp turns.  The closer you can get the two poles together, the stronger the magnetic field will be (in gauss).  For the purposes of attracting or repelling permanent magnets, wrapping your magnet only partially around the coil would likely work best.

A good example would be to look at some industrial magnets, like http://www.magnetechcorp.com/Round.htm .  For that magnet, the outer material is likely some form of iron or steel.  When looking at their opposite pole magnets (they have one listed on their site), they have the same outer shield, but it's made of a non-ferrous material (likely aluminum).  Mattering on your application, you can use a 'U' shape (with one leg of the U having the coil wrapped around it) or an 'E' shape (with the center leg having the coil wrapped around it and the outer legs being the opposite pole as the center).