Electromagnet Optimization

[Mech133]

Hello, I am looking to design an electromagnet with the greatest flux possible. I am working with very limited power as well as overall volume the coil can occupy. I am using this coil to repel a permanent magnet when pulsed. I am currently using a Si-Fe laminated core of about .250" in length with a .100x.100 cross sectional area. Power is DC and voltage is limited to about 5v at about 500mA. The coil I have now uses about 400 turns. The load I need to move is rather small ~5g. The current setup works well but I would like to use an even smaller core if possible. My question is what can be done to maximize the flux between the coil and the magnet. I know reducing the gap between them will increase the force but a problem I am finding is that at low power the permanent magnet seems to overcome the relatively low output of the electromagnet and actually attract the steel core rather than repel until they are seperated to a farther distance. Height is the dimension of concern as there is more leeway with the diameter of the coil. Will decreasing the height and increasing the diameter lead to a stronger coil at lower power? What effect will changing the shape or size of the core have? Are there better core materials than Grain oriented silicon steel for use at lower power? Also is it possible to shape the core so as to concentrate the flux in a certain direction?

Thanks for any help!

 

[israelkk]

Why do you use laminated core if this is a DC electromagnet? Laminated is used in an AC electromagnet to avoid Eddy current losses.

Why are you repelling a magnet? You may use a "push" electromagnet where the gap can be as small as you want. What is the outside diameter and length limitations of the electromagnet? You may find a stronger electromagnet.

Do you have the knowledge to design an electromagnet or you are looking for someone to optimise and design one for you?

http://www.webspawner.com/users/israelkk/

 

[Mech133]

The laminations are being used because that is what is readily available. Do laminations cause a degradation in DC magnets or only not add any benefits? If they do cause detrimental effects what is the best core material for a low power DC magnet?

repelling a magnet is necessary in this particular design. The electromagnet has dimensions of about .225" in height by .350" in dia. currently. The dia could be increased to prob more like .500 max.

I am no magnetic expert but am trying to get a handle on how to maximize my field using the smallest volume and power possible.

 

[israelkk]

To maximize the magnetic field you will need to use a FEA magnetic software or a specific software to optimize the electromagnet. I suggest that you will get someone who has experience with electromagnet design and analysis.

Few years ago I had to develop an electromagnet 0.6" by 0.6" to have a pull force of 200 grams from a 4 mm distance.

A drawing of the electromagnet and the permanent magnet setup will be helpful.

 

[dgallup]

You can use FEMM software for 2D static analysis. It has some limitations but it is free. At high flux densities the material properties do not properly join the "air line" so you will get wildly over optimistic force calculations. I use MagNet from Infolytica which is a much better program but far from free.

http://femm.foster-miller.net/Archives/readme.htm

 

[Mech133]

I have made progress in my design but am getting hung up on a seemingly easy equation. I have found equations on this forum and elsewhere stating Field Strength (H)=NI/l

This gives units of ampere-turns/meter

I have a coil of 450 turns, using .3A

The coil is wound on a bobbin with a straight core running through the center of it and is .250" long.

Plugging these numbers in 450T*.3A/.00635m =21260 AT/m

This number seems to be much too high from B-H curves I have looked at. Is there some other equation for coils of this type?