Electromagnet

[Raider5678]

Hello, I was commissioned at work to design, engineer, and build, an electromagnet prototype that has a dial on it that can be turned up or down to increase/decrease the power of the magnet.

It needs to be able to lift 30 pounds.

 

So I've gotten the formula that the strength of the magnetic field is related to turns times amps. 

However, how can I relate this formula to newtons of force applied at a given distance?

 

Ironically, my boss didn't specify if it needs to be able to lift a weight of 30 pounds from 12 inches away, or direct contact.

So I'm assuming he wants 30 pounds from 3 inches away. That I believe can be plugged into the formula for distance, because I feel that distance would definitely play a role in the strength of the magnetic field. Let's assign that the variable of D.

 

So, given that T = turns, A = amps, D = distance, how can you find N = newtons of force?

I'm assuming there are more variables, but this is a general idea.

 

 

 

 

Additionally, another question I have is the resistance of the wire thickness.

Thinner wire has higher resistance, however, it allows you to get more turns onto the magnet, so what would be an idea gauge? 

I think I can figure this out using the algebra on a graph and find the point that the two lines connect to each other, but a formula would be nice if I don't have to make one on my own.

 

 

 

And, a final question is does anyone have any ideas on how to keep the magnet cool? The electricity passing through the thin wire would create a lot of heat, and I know that's bad. But I'm at a loss on how to cool down a portable electromagnet.

 

Also, if I can successfully do this I'll get a lot more jobs like this.

So it's fairly important to me.

Edited January 30, 2018 by Raider5678

[studiot]

My class notes from 50 years ago should help you.

 

[Bender]

The problem as presented is highly nonlinear and depends on the shape and thickness of the object you want to pick up. The problem with studiots notes is that B varies greatly with magnetic resistance, which is very large in air. In the configuration shown in the notes, the magnetic field has to curve from the top all the way down through air.

You will get a higher force with a U-shaped iron core, on the condition that the distance between the legs of U is bigger than the distance to the object. Otherwise you loose too much flux lines.

Thick or thin wires don't matter for the strength, only for the type of power supply, as it is the current density, which is important.

Heat production can easily be calculated with the resistance of the copper wire. Cooling can increase the max current density, but also takes space. It depends on how long it needs to operate.

[John Cuthber]

On 30/01/2018 at 3:26 PM, Raider5678 said:

Ironically, my boss didn't specify if it needs to be able to lift a weight of 30 pounds from 12 inches away, or direct contact.

You need a better boss.

[studiot]

16 minutes ago, Bender said:

The problem with studiots notes is that B varies greatly with magnetic resistance, which is very large in air. In the configuration shown in the notes, the magnetic field has to curve from the top all the way down through air.

 

Yes it's a very basic start, but Raider clearly doesn't care about the subject any more.

30lbs lifting is a very small amount for an electromagnet.

They were lifting tons, well over 50 years ago.

[Raider5678]

1 hour ago, John Cuthber said:

You need a better boss.

He's getting a bit senile but he's a nice man.

1 hour ago, studiot said:

Yes it's a very basic start, but Raider clearly doesn't care about the subject any more.

30lbs lifting is a very small amount for an electromagnet.

They were lifting tons, well over 50 years ago.

3

What do you mean I don't care about the subject anymore?

Ultimately I found some other online information that allowed me to work it out better and more exactly.

http://www.daycounter.com/Calculators/Magnets/Solenoid-Force-Calculator.phtml

 

Edited January 31, 2018 by Raider5678

[Bender]

Note that that calculator is only valid if the magnetic core is significantly larger than the distance. The volume of the coil also needs to be sufficiently small compared to the core to limit fringe effects inside the coil.  

[Raider5678]

5 hours ago, Bender said:

Note that that calculator is only valid if the magnetic core is significantly larger than the distance. The volume of the coil also needs to be sufficiently small compared to the core to limit fringe effects inside the coil.  

Fringe effects?

[Bender]

Some magnetic field lines will curve back inside the coil or somewhere else you don't want and not contribute to the force.

As air gaps increase (the coil itself is also an air gap), fringe effects become more important.