# How to obtain the magnetic force?

How to obtain the magnetic force??

Hi ,

I didn't have any experience to design coil and permenent magnet .

Now i have to do one project using coil and magnet NdFeB. But i haven't got the maximum force. (need maxi force between 1300 to 2500)

I am doing the below procedure. Is it correct???
using DC supply 48V,
known value :core internal and external diamer, length
1. choose the wire size (From AWG spec)
2. calculate the number of turns / layer (turns/inches * core length)
3. calculate the number of layers (turns / inches * core thickess)
4. calculate total no of turns (Step 2 * Step 3)
5. calculate the wire length (using AWG spec's : ohm / km)
6. calculate the resistace and current.
7. calculate the B using (B = u0 * N*I/L)
8. calculate Force using (F=B*I*L(length of wire)).

Do i need to consider NdFeB magnet mass and B in this calculation??? How can i get the force??

Anybody helps me?

Thanks in advance for the help.

What are your units of force?

And why is the core material hollow?

I assume you want the force between the perm magnet and electromagnet when they are aligned north to south.

You left out some specs.

What is the shape of the NdFeB magnet and what is it's rating?

I want the force between permenent magnet and electromagnet.

Force unit is Newton to design.

I considered that the core material is air core. Is it possible???

And then the shape of NdFeB is Ring Type.

Specification for NdFeB
Dimensions: 3/4" od x 1/2" id x 3/8" thick
Magnetization Direction: Axial (Poles on Flat Ends)
Weight:*0.399 oz. (11.3 g)
Pull Force, Case 1:*16.30 lbs
Pull Force, Case 2:*21.12 lbs
Brmax: 13,200 Gauss
BHmax: 42 MGOe

Do i need to consider anything to get the maximum force???

Thank you Phark.. Gokul43201
Staff Emeritus
Gold Member

There's no easy way to calculate the force; it depends on the axial component of the gradient of the net magnetic field produced by the two magnets.

Thank you for your reply, Gokul Do you mean that I need to find out the net magnetic field B produced by the permenent magnet and electromagnet (Coil)? How can I solve that one?

Now I am finding out the magnetic field B (z) at a distance from the center of a coil again.
So could I use Brmax for permenent magnet from NdFeB specification?

Any idea to solve this problem???? Yes, you can make an electromagnet without a core. If it's a cylindrical in shape, it's called a solenoid.

As Gokul says, it's not an easy problem. If you can't put a problem in mathematical analysis down, and can do calculus you might find it interesting, otherwise there's always experimentation.

You could sum the contributions to the B field at an arbitrary point in space due to the solenoid. Treat the solenoid as the sum of rings of current. For a single layer solenoid this is easiest. You add up the contributions from a bunch of rings all having the same diameter. By add, I mean integrate. If the inner windings are much less in diameter than the outer windings, you will need to take that into account with a double integral.

Next you consider how the field acts on the neodymium magnet which you treat as bunch of magnetic dipoles. I'm not sure how this is done. Somehow we would need to figure out the dipole strength per unit volume of material given the specs of N42...

However it might help if you said what you had in mind with this project.

Last edited:
Gokul43201
Staff Emeritus
Gold Member

Any idea to solve this problem???? Yes, you would have to model the system on a Finite Element package (like COMSOL or ANSYS). You will not get anywhere close with paper and pencil.

The easier approach is to solve it experimentally.

Yes, you would have to model the system on a Finite Element package (like COMSOL or ANSYS). You will not get anywhere close with paper and pencil.
If you were to apply finite elements, how would you model the perm magnet give the material data sheet?