# Is it practical to make an electromagnet that causes a 200N force?

• TimT
In summary, the goal of the project is to create an electromagnet that will attract a loose piece of iron with at least 200N of force. The electromagnet will work best if the magnetic circuit is good. Variations in the current through the solenoid could allow for accurate force control.f

#### TimT

I'm trying to construct an electromagnet that, when a loose piece of iron is inside the solenoid, will create a field that will attract that piece of iron with at least 200N of force. My thought is that I can fill half of the solenoid with an iron core, leaving space in the other half for the loose piece of iron. I've tried to draw a picture of what I'm thinking below.

http://tinypic.com/r/2jdjak9/6
http://tinypic.com/r/2jdjak9/6

Can anyone tell me if this is something practical that I can make?

Dc solenoid actuators probably generate over 200N (~20 pounds) force, when pulling in the iron plunger. The highest force is probably in solenoid actuators with T-shaped plungers. As the gap in the iron gets smaller, the force gets larger, and when the gap is ~1 mm or less, the force is very high. There is a wide variety of commercial solenoid actuators available.

Having a good magnetic circuit is very important. Most of the magnetic energy in the magnetic circuit is actually in the air gap. If W is the stored energy in the gap, then the force in direction x is the partial derivative

Fx = ∂W/∂x, so the force is very high when the magnetic gap is small.

Bob S

I am not so sure about your design especially I wonder if the metal on the bottom will cause enough of a field gradient.

A question you need to answer is, how far your piston has to travel. Making something stick with 200N force is much easier than pulling is over some distance.

200N is very much achievable. I would build a smaller model measure the force, and then use theory to scale it up.

Thanks so much for the replies. My goal is have the force on the plunger be relatively constant over the distance it travels. Or, to phrase it another way, a person pulling on the plunger would have to exert a constant force of 200N to bring the plunger out from a fully depressed position (except perhaps with a barrier to prevent the plunger from actually touching the iron core.) Do you think this would be approximately the case if I use a solenoid actuator of about an inch long?

Also, could I vary the force required to pull the plunger with reasonable accuracy by varying the current through the solenoid?