# Building an electro magnet

1. ### 215

39
Hey guys..

I trying to build an magnet which can pull an object with 5N..

I am using S37 as my the iron for my horseshoe magnet,

And been using this formula to convert Newtonian Force to magnetic force

$\vec{F}=\frac{B}{µ0}*A$

A= cross sectional area = 0,002*1/100 M^2
B = Magnetic Force
µ0(permeability in vacuum) = 4$\pi$*10^-17

B_gap(x) =$\frac{µ0*I*N}{\frac{l_j}{µj}+2x}$
l_j: the length of horseshoe = 2 CM
µj: permeability of Steel37.. Can't find it using google.. :(
x: airgap distance between each legs and the materiel it should attract. = 0,002m

I am using 1 A, I tested my calctulation with 3N, which using my calculation says that i need 600 windings, but i seem to extreme..

The reason why i think this is not true is because 600 winding => 2 (0.002 + 0.01)*600 M copper wire=> R=0,079 ohm => V =0,079V..

Is it too extreme?

Last edited: Apr 26, 2013

### Staff: Mentor

Not sure what you mean by "too extreme".... are you thinking that the voltage required seems awfully low? I haven't checked your calculations, but it doesn't take much voltage at all to drive one amp through a length of copper wire. You will probably have to consider the inductance of the coil as well as the resistance of the wire to completely understand how your setup will work.

You could do worse than actually wiring up an electromagnet with some number of turns, see how close your calculations are. But if you do.... Don't use a voltage high enough to hurt yourself or anything near you, and think about your current-limiting devices. You're basically trying to build a controlled short circuit here.... Resistors and fuses are your friends.

3. ### 215

39
My caluculation is kinda simple..

Assume that the magnetic force from the iron core is the same as the one in the gap.

I know that I need the magnet to pull 5N

Which means that
F=$\frac{b}{µ0}*A$

Where A =0,002*1/100
<=>
5 =$\frac{b}{µ0}*A$
<=>
B =3.14159*10^-11

Then i solve N using the other equation and then i get 1001 winding.

4. ### SteamKing

9,133
Staff Emeritus
A = 0.002 * 1/100 is a rather curious expression. What units does it have? How did you calculate it?
(your comma is my decimal point)

5. ### 215

39
Yeah... the metal plate i bended needed to be 2mm thick, and the lengt of it is 1cm..
A is Cross-sectional area in M^2

Last edited: Apr 26, 2013