1761

Item 1761

OTHER: Electrical - Motor - Rotor - Permanent Magnet

Notes:

See; Permanent Magnet Motor Technology, Chapter 2 - Permanent Magnet Materials and Circuits.

Database ~ Motor: Form - Magnet
The information in green is in the above database, along with additional information.

Br is the measure of its residual magnetic flux density in Gauss, which is the maximum flux the magnet is able to produce. ( 1Gauss is like 6.45 lines/sq in) (1 gauss is equivalent to 10^-4 T), Gauss is an obsolete term.
Hc is the measure of the coercive magnetic field strength in Oersted, or the point at which the magnet becomes demagnetized by an external field. ( 1Oersted is like 2.02 ampere-turns/inch)
BHmax is a term of overall energy density. The higher the number, the more powerful the magnet.
Tcoef of Br is the temperature coefficient of Br in terms of % per degree Centigrade. This tells you how the magnetic flux changes with respect to temperature. -0.20 means that if the temperature increases by 100 degrees Centigrade, its magnetic flux will decrease by 20%!
Tmax is the maximum temperature the magnet should be operated at. After the temperature drops below this value, it will still behave as it did before it reached that temperature (it is recoverable).
Tcurie is the Curie temperature at which the magnet will become demagnetized. After the temperature drops below this value, it will not behave as it did before it reached that temperature. If the magnet is heated between Tmax and Tcurie, it will recover somewhat, but not fully (it is not recoverable).
(please note that this data is from www.magnetsales.com)

Material	Br	Hc	BHmax	Tcoef of Br	Tmax	Tcurie
NdFeB	12,800	12,300	40	-0.12	150	310
SmCo	10,500	9,200	26	-0.04	300	750
Alnico	12,500	640	5.5	-0.02	540	860
Ceramic or Ferrite	3,900	3,200	3.5	-0.20	300	460

Magnetic Materials:

PROPERTIES OF MAGNETIC MATERIALS http://www.astro.uvic.ca/~tatum/elmag/em12.pdf

Diamagnetic, Paramagnetic, and Ferromagnetic Materials http://www.ndt-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/MagneticMatls.htm

Ferromagnetism http://en.wikipedia.org/wiki/Ferromagnetic

FERROMAGNETIC MATERIALS http://www.phys.unsw.edu.au/PHYS2939/pdf/Ferromagnetic_Mats.pdf

In ferromagnetic materials, small regions with a particular overall spin orientation are termed domains.

This strong (large) spin alignment leads to huge permeabilities:

Material Relative Permeability μ_r

Nickel 250

Cobalt 600

Iron (pure) 4,000

Mumetal 100,000 (aka μ-metal) is an alloy of iron (~25%) and nickel (~75%) + small % of other elements.)

Paramagnetic metal:

Aluminium ≈1

Titanium is Paramagnetic

Ferromagnetic Materials http://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_4/advanced/t4_1_3.html

MAGNETIC PHENOMENA IN FERROMAGNETIC MATERIALS http://physics-animations.com/Physics/English/mag_txt.htm

Magnetic Properties. If a metal is placed in a magnetic field, a force is exerted on it. The intensity of the magnetization, called M, can be measured in terms of the force exerted and its relation to the magnetic field strength, H, depending upon the susceptibility, K, which is a property of the metal.

Metals have a wide variance in susceptibility and can be classified in three groups:

The diamagnetic substances in which K is small and negative, and thus are feebly repelled by a magnetic field; examples are copper, silver, gold and bismuth.
The paramagnetic substances in which K is small and positive, and thus are slightly attracted by a magnetic field; the alkali, alkaline and the nonferromagnetic transition metals fall in this group (it can be seen that titanium is slightly paramagnetic).
The ferromagnetic substances, which have a large K value and are positive; iron, cobalt, nickel, and gallium fall under this heading. An important feature of this group, besides the strong attraction in a magnetic field, is the fact that these metals retain their magnetization after being removed from the magnetic field.

Cooling:

Large PM brushless motors can achieve a higher possible efficiency than any other electric motor (except those with superconducting excitation windings). Thc limitation, however, is t,lw high price of PM materials. NdFeB magnets offer the highest energy density at reasonable costs. Their major drawback, compared to SmCo, is temperature sensitivity. Performance deteriorates with increased temperature, which has to be taken into account when the motor is designed. Above a certain temperature, the PM is irreversibly demagnetized. Therefore, the motor's temperature must be kept below the service temperature (170" to 250°C) when using NdFeB magnets. ..... The rotor losses in PM synchronous motors are small so most PM machines employ passive cooling of their rotors. [Source ~ PMMT p.353]

Halbach Array:

Advantages: A fundamental advantage of a machine of this type is that the machine can be constructed without the use of magnetic material other than the permanent magnets. There is no need for laminations or back iron. This has two major advantages. First the conventional core loss and eddy current loss in the laminations or back iron does not exist. The only loss in the machine will be losses in the windings. The second advantage is since there is no back iron or laminations required the machine is inherently lightweight.

Halbach magnet array; ~

Halbach Array Motor/Generators ~ A Novel Generalized Electric Machine

http://www.tip.csiro.au/Machines/papers/iwscem/index.html

Build a Halbach array; http://www.matchrockets.com/ether/halbach.html - http://www.otherpower.com/danf/halbach.html

MAGNETIC FORCES INSIDE PERMANENT MAGNET ASSEMBLIES ~ http://www-sldnt.slac.stanford.edu/nlc/notes/Bowden_Eng/ABC_TechNote-067_2.pdf Have hard copy.

The Aurora - Solar-powered electric vehicle had an ironless air-gap winding.

Definition;~ http://en.wikipedia.org/wiki/Halbach_array Have hard copy.

http://www.gaussboys.com/pages.php?pageid=6

Halbach array has the following advantages: from [Source ~ AFPM p.111]

The fundamental field is stronger by a factor of 1.4 than in a conventional PM array, and thus the power efficiency of the machine is doubled.

The array of PM,s does not require any backing steel magnetic circuit ....

The magnetic field is more sinusoidal...

Halbach array has very low back-side fields.

http://www.cip.csiro.au/Machines/papers/DesignOfAnInWheelMotorForASolarPoweredElectricVehicle(IEE).pdf#search=%22%22laminated%20core%22%20%22permanent%20magnet%22%20layer%20stator%20%22axial%20flux%22%22

Design and Analysis of High Speed Slotless PM Machine with Halbach Array ~ High speed???

RC Groups ~ Discussion - Axial flux bldc motor - Looks interesting.

"Optimization predicted that design with the Halbach magnet arraignment would have approximately 10W (20%) less loss than an equivalent arraignment of the same total mass, with magnets on backing iron" ~ CISRO

Due to the trapezoidal shape of all the magnets it appears to me that each magnet will be held in radial position by the magnet on each side.

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Idea for a Partial Halbach Array: