Combined electromagnet and permanent magnet, c shaped with permanent magnets in the air gap 1

[alphamaleomega]

I am working on an induction disc braking device that typically uses permanent magnets to create eddy currents and generate heat and drag, however, I desire to use a combination of electromagnet and permanent magnet for control purposes. The magnets are mechanically positioned to create a base drag then electromagnets are activated via pulse width modulation.

The c shape is made of 3.5" wide x 1/2" thick 8" long mild steel flat bar, each leg is welded to a 4" square tube, so the two legs are perpendicular to the square tube and separated by .5" + .5" + 9/16" or 1 9/16" apart.

The permanent magnets are mounted flush on the inside face of the flat bars so as to create an air gap of 9/16" between the magnets. The poles are opposite to one another. There are two 1.5" diameter x .5" permanent magnets on each leg, they are samarium cobalt permanent magnets.

I plan on winding the coils around the flat bar in the first 4" of the 8" bar. I desire low voltage high current, not that many windings 24V

I assume the permanent magnets will spread much of their field into the iron flat bars, the magnetic fields should be additive, the electro magnet flux plus the permanent magnet flux.

I need an Opra analysis of this magnetic circuit, but for preliminary design I am asking if my assumption on the fields being additive is valid and what losses would be incurred in the permanent magnets by being attached to the iron bars.

Thanks

 

[MagMike]

The fields will be additive, but I believe you will find that you need a prohibitive amount of amperage to produce a significant effect on performance. In addition, response time of the electromagnet will be difficult to control.

 

[alphamaleomega]

HI Magmike

Thanks:


I am looking at the Adamsmagnetic web site and have selected magnets based on the ability to transfer energy, which is I assume is a function of not only field strength, but also the interaction of the magnet and the material it is inducing the current into. Some sort of saturation involved? These magnets are expensive about $75 per copy. I have multiple rotors and a control bar that changes the physical location of the magnet to the face of the disc.

So the c magnet electromagnet strength is very small compared to the permanent magnets? I am limited to low voltage, but could go high voltage if I encased the coils in a sheathing to make the assemble intrinsically safe.

What is your line of work? Do you do magnetic circuit modelling?

JM

 

[racookpe1978]

Why would expect the permanent magnets to not act as a "permanent brake" - certainly not as strong as the Permanent + electromagnet combined forces - but it appears they would be always acting as an extra friction on the assembly.

 

[alphamaleomega]

The eddy currents are produced only during high angular velocity, and the actuator bar brings the magnets into proximity with the rotor. There is no static holding force.

 

[LionelHutz]

Just asking - how well will the permanent magnets work as part of the electromagnet field path?

 

[MagMike]

@Lionel: Depending on the polarity of the electromagnet, the permanent magnets will have an additive or negative effect.

@Alphamaleomega: My day job is designing magnet assemblies, both permanent magnets and electromagnets.

 

[waross]

Does the air gap play a big part in determining the flux density and strength?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

It should be fairly obvious to everyone here that the electromagnet and permanent magnet fields will either add or subtract.

I guess I will ask the question a different way - Will the permanent magnets saturate due to the extra flux from the the electromagnet?

 

[MagMike]

Not likely, if the design uses NdFeB or other Rare Earth magnet material. NdFeB requires extremely large magnetic fields to be magnetized and/or saturated.