Electromagnet and core permeability

In summary, the conversation discusses the energy input needed to make a magnet drop off when attached to an electromagnet with a steel core. It explores the effects of core permeability on the efficiency of the electromagnet and the factors that may affect this efficiency, such as the size of the core and the strength of the magnet. Equations relating to energy input and flux generated by the electromagnet are also mentioned. The conversation concludes by suggesting that further experiments and consideration of the geometry of the permanent magnet may be needed to find a solution.
  • #1
capthook
13
0
A magnet is attached (or over a small airgap) to the end of an electromagnet (EM) with a steel core, then the EM is pulsed with just enough juice to get the magnet to drop off. (just negating the attraction)

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
 
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  • #2
You need to post some equations relating the energy input versus the flux generated by the electromagnet...
 
  • #3
Hi Berkman - thanks for the reply.

Don't know why you moved this... it's not a homework question...

The equations of input vs. flux is not the issue, rather the relative performance of different core permeabilities. A higher permeability core in a motor application will perform better - more flux per watt input.
However, in this odd application, I'm unsure of how the permeability will affect the efficiency per my 1st post.

- -
If equations are helpful:

flux density = Ampere-Turns/length of the core material X ur

Turns=number of turns of wire
length=measured in meters
u=permeabilty of free space/air/vacuum 4pi x 10^-7
r=relative permeability

A bolt that is .1 meters long (about 4 inches) with diameter of .01 meters(about .4 inches), the cross-sectional area of the bolt/nail would be .00007854.

For iron, r=50. r X u =.00006283. 1 Tesla divided by .00006283 is approximately 16000 Ampere-Turns/meter. 16000 X .1 meters(length of the core) is 1600 Ampere-Turns. If the coil resistance is 10 ohms and you wish to use 1 Amperes then you'll need 10 Volts. With 1 amperes you'll need 1600 turns of wire.(1 Amperes X 1600 Turns = 1600 Ampere-Turns).

The power consumption for the coil would be 10 Volts X 1 Ampere = 10 Watts.
At repulsion when the electromagnet is energized, force is calculated like this:

F=B^2A/2u

B=Total Tesla which in this case is 1(electromagnet) + 1(permanent magnet) =2
A=in this case .00007854
u=4pi X 10^-7

F=2^2(4) X .00007854/2 X 4pi X 10^-7=125 Newtons

(1) H in AT/m=NxI/length

(2) B in Tesla=H x (.000001256 x 800)

2000 Gauss=.2Tesla ur=.0010048
.2/.0010048=199 AT/m

H=N x I/5.08 199 x 5.08=1011 AT
 
  • #4
Sounds like a pretty complicated case. What shape is the permanent magnet? If it is a horseshoe magnet, with both poles exposed to the electromagnet face, will it ever fall off?

And if it is a slug magnet, will it fall off, or will it just flip as you get near to matching the interface flux? Remember that the electromagnet attracts the permanent magnet by virtue of the ferrous material that the permanent magnet is made of... Just opposing the permanent flux may not be enough to make the permanent magnet "fall away"... You may have to define the geometry of the permanent magnet more closely in order to work toward a solution.

BTW, have you tried this experiment? Might be good to run a few trials to see what the mechanical behavior looks like, to help your calculations.
 

1. What is an electromagnet and how does it work?

An electromagnet is a type of magnet that is created by passing an electric current through a wire wrapped around a core material, such as iron. This creates a magnetic field around the coil, which can be turned on or off by controlling the flow of electricity.

2. What is the purpose of the core material in an electromagnet?

The core material in an electromagnet serves as a pathway for the magnetic field to flow through, increasing the strength of the magnet. It also helps to concentrate and direct the magnetic field in a specific direction.

3. How does core permeability affect the strength of an electromagnet?

Core permeability is a measure of how easily a material can be magnetized. A higher core permeability means the material is more easily magnetized, resulting in a stronger magnetic field in the electromagnet.

4. What factors can affect the permeability of a core material?

The type of material, its composition, and its physical properties (such as temperature and pressure) can all affect the permeability of a core material. In general, materials with a high iron content, such as iron or steel, have a higher permeability than non-magnetic materials like copper or aluminum.

5. How can the permeability of a core material be measured?

The permeability of a core material can be measured using a device called a permeameter. This instrument applies a magnetic field to the material and measures the resulting magnetic flux density, which can then be used to calculate the permeability of the material.

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