# Need help making a suitable electromagnet to repel a 2.5" permanent magnet

Robertjpaul
Hi all.

New to the forum and new to making electromagnets. I want to pick your brains as I know extremely little about electromagnets.

So I have a 2 1/2 inch round x 1 inch thick rare Earth magnet that I’m trying to repel with force using an electro magnet. The repel would be in bursts. I know the rare Earth magnet is rated for around 400 pound lift. Also I’m using a 12v car battery for my experiment.

My questions are.

What diameter and length iron would work best.

What gauge magnet wire do you recommend?

How many turns do you feel is needed for this magnet?

What amps would get me the most power or adequate power for my experiment?

I know nothing about any of this. I’ve tried searching but I keep finding equations I don’t understand.

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Cutter Ketch
Hmmm ... a little hard without equations, but also we would need a little more specification. Let’s see if I can say anything useful.

400 pounds is how much the magnet can lift when stuck directly to iron. The amount of force you can generate attracting or repelling it with an electromagnet is really only limited by how big of an electromagnet you can make and how strong of a (non magnetic) structure you can make to hold everything. It will be very easy to generate dangerous forces, so think hard about how strong everything is and whose fingers are in the way if things fail. Although not the most likely scenario, you could even launch the magnet at high speed, so be careful!

You didn’t say what you wanted to float or how high. I’ll assume you want to float the bare magnet and just high enough to see it is floating (1/4 inch?). The strength of your electromagnet isn’t going to be your problem. Your permanent magnet is very strong and you would have a hard time pushing it close to an opposed pole of a magnet of just about any strength. The trick is keeping it from flying/ falling off, or perhaps more likely, flipping over.

The simplest approach is to cheat, simply constrain the permanent magnet so it can’t do anything but move away. A close fitting see through tube would be one way.

Making it free float is much harder. It essentially can’t be done with just static magnets. You either need diamagnetic materials involved, or you need some sort of active stabilization.

To make a strong magnet, more windings in a smaller circle makes a stronger magnet. For this reason people invented magnet wire. Magnet wire is super small gauge and has a very thin varnish of insulation to allow as many wires as possible in the winding. You don’t need much insulation because the voltage is low. The limit is when the resistance of the wire creates enough heat in the winding to melt the wire. If don’t intend to control the current, you have to make the winding long enough so the resistance is high enough so the current is low enough that the wire doesn’t over heat. You mentioned you might be pulsing the current, so that can also keep the average power and heating down. Usually the design goes toward a gazillion windings of tiny wire, thus magnet wire.

SergioPL
Robertjpaul
Hmmm ... a little hard without equations, but also we would need a little more specification. Let’s see if I can say anything useful.

400 pounds is how much the magnet can lift when stuck directly to iron. The amount of force you can generate attracting or repelling it with an electromagnet is really only limited by how big of an electromagnet you can make and how strong of a (non magnetic) structure you can make to hold everything. It will be very easy to generate dangerous forces, so think hard about how strong everything is and whose fingers are in the way if things fail. Although not the most likely scenario, you could even launch the magnet at high speed, so be careful!

You didn’t say what you wanted to float or how high. I’ll assume you want to float the bare magnet and just high enough to see it is floating (1/4 inch?). The strength of your electromagnet isn’t going to be your problem. Your permanent magnet is very strong and you would have a hard time pushing it close to an opposed pole of a magnet of just about any strength. The trick is keeping it from flying/ falling off, or perhaps more likely, flipping over.

The simplest approach is to cheat, simply constrain the permanent magnet so it can’t do anything but move away. A close fitting see through tube would be one way.

Making it free float is much harder. It essentially can’t be done with just static magnets. You either need diamagnetic materials involved, or you need some sort of active stabilization.

To make a strong magnet, more windings in a smaller circle makes a stronger magnet. For this reason people invented magnet wire. Magnet wire is super small gauge and has a very thin varnish of insulation to allow as many wires as possible in the winding. You don’t need much insulation because the voltage is low. The limit is when the resistance of the wire creates enough heat in the winding to melt the wire. If don’t intend to control the current, you have to make the winding long enough so the resistance is high enough so the current is low enough that the wire doesn’t over heat. You mentioned you might be pulsing the current, so that can also keep the average power and heating down. Usually the design goes toward a gazillion windings of tiny wire, thus magnet wire.
Yeah I guess I missed a few details. Sorry, I know they make all the difference.
So, yes the electromagnet will be held in place by a fixture. The permanent magnet will also be held but it will be allowed to move away from and back to the electromagnet. I plan to have a variable control for the power as to control it.
I want to see how fast I am able to repel the permanent magnet with as much strength as allowed without over powering the permanent magnet.
Thanks so much for the info though. It does help.

Thanks,
Rob