# How to Calculate the Number of Turns of Wire needed on a Iron Core Magnetic Solenoid

I was referd to this forum from a friend and I have been reading some of them and I think you guys can help me and I would be very happy if you could.

I was taking a electormagnitism physics class in school, calc based, and I had this idea for a project. I know that to calculate the magnetic field that is F=I*L*B*sin(thata) and the magnetic field of a solenoid is B=(u*n*I)/(2R) and n=turns/length. The question I have is how do I calculate the number of turns a solenoid needs when it has an iron core and what core to choose? I have been reading outside of class about fearite and iron powder cores and it seems they have a class for each but I don't understand them. I havn't even decided if I should use a tipical solenoid or a toroid either.

I am trying to find out if I can make a electromagnet that is roughly 5" high, 11" wide, and
12" long(this may have to be shorter), that runs on 20 amps, 12-24V DC, and has a 25,000-60,000N pull force on it (would really like to hit that max but not being picky). I realize I have taken only one physics class about magnetics and this sound rediculus so if it can't be done it wont't hurt my fealings none. Thanks for any input.

Here's a link talking about how to calculate the magnetic field with an iron core,

http://en.wikipedia.org/wiki/Electr..._.E2.80.93_the_constant_B_field_approximation

From that, it talks some about calculating the force on another magnet.

I think 25000 - 60000 N is really high, but with enough turns I'm sure it can be done lol
I don't know if you could manage to fit those dimensions though.

That would be pretty dangerous to use, what do you need it for?

Would multiple smaller electromagnets in a case that size work better? Would the force of each magent add up or does it not work that way?

I think they add, just as adding turns to one coil adds B field. But it will be less efficient because there will be some separation between the coils.

I think the best way would just be a single coil with as many turns as necessary.

I suggest building it, measuring the strength with some number of turns, and measuring again with x many more turns. Then you could do some algebra to figure out approximately how many turns you need.

That article says something about saturation of the core and becoming nonlinear, but I wouldn't worry about that for now.