Home made electromagnet

[Iplayfarmer]

I'm with some of the previous posters. Just use permanent magnets. You shouldn't have to use electricity. Line your magnets up so that like poles are facing each other, and you'll get the maximum repulsion. You're going to need a lot of magnets or very big magnets, though.

When I was a kid, one of the best christmas presents my family ever got was a stack of about 5 donut magnets. We'd stack them on a pencil with like poles facing and play all kinds of games. None of us kids could ever get all five of the magnets to actually touch no matter how hard we pressed our pudgy little fingers together. I'd bet you could use this concept with a buch of rods on a top plate that fit in holes on a bottom plate. Put a few donut magnets around each rods correctly oriented and voila... Levitation. You'll still need a lot of rods and a lot of magnets, and you won't get much levitation, but the principle is sound, I think.

I also think you'll have to use non magnetic materials for the plates. Wood might be a good options as it's easy to get and easy to work.

 

[Brad_Blazer]

I like the ring magnet idea. At work we run lots of magnetrons (ala microwave ovens) to generate the powerful UV light needed to cure resin in a continuous process. The magnetrons have a very finite life after which they are scrapped. They also contain some pretty good ceramic ring magnets. It is a little work getting them apart but I have done a few.

 

[Prateek]

Hello Friends,
Iam currently doing a project for my college, a part of which involves the construction of an electromagnet(DC) that can push and pull a permanent magnet. The permanent magnet is attached to a link. My calculations show me that the force of attraction and repulsion between the electromag. and permanent magnet has to be 50 Newtons(accuracy not an issue as long as it attracts and repels).
There is restriction on space- max. length=40cms, max. width=20cms.

So my question is how many turns and of what gauge do i need for the electromagnet? i got the core from my doorbell.
Please help!

 

[rScotty]

I'll be glad to help. And enough people here are interested in solenoids that it might be interesting for others too. If not, we can take it off line. First of all we need to know something about the forces available.... that would be the parts that you already have. I suggest we divide the solenoid design into the permanent magnet part and the electro-magnet part.

For the permanent magnet it would be nice to know it's shape, history, material, and magnetic field strength...but we can make pretty good guesses from whatever you do know about your permanent magnet.

For the electromagnet winding I agree that using your laminated core sounds good. What kind of wire do you have available? and Most importantly, what source of electricity do you have in mind? A DC supply will require switching the polarity - probably manually - to go from push to pull. An AC supply will reverse at whatever the frequency is.

If we know those things I can show you how to calculate the solenoid's force. Keep in mind that magnetic force falls off rapidly with distance. The two parts of the solenoid need to be close together and cannot move very far.
BTW, what's your name?
Enjoy! rScotty

 

[SPYDERLK]

SNIP...
For the electromagnet winding I agree that using your laminated core sounds good. What kind of wire do you have available? and Most importantly, what source of electricity do you have in mind? A DC supply will require switching the polarity - probably manually - to go from push to pull. Enjoy! rScotty

You wont need a laminated core with a DC powered magnet. It offers no benefit other than on speed of starting and stopping the magnetic effect. This application doesnt require a quick magnetic response on the order of milliseconds.
larry

 

[Treemonkey1000]

Why not use an air cushion? Admittedly I didn't read every posting on this thread. Air cushion could be turned on and off to levitate a fair amount as well.

 

[rScotty]

You wont need a laminated core with a DC powered magnet. It offers no benefit other than on speed of starting and stopping the magnetic effect. This application doesnt require a quick magnetic response on the order of milliseconds.
larry

Good point - and a good catch. I agree. Laminations aren't magic or necessary....in fact they are a slight detriment for devices that reverse magnetic polarity at fairly low speeds. If you have a laminated part that physically fits then we can use it. Otherwise just use a chunk of iron or mild steel.
rScotty

 

[Prateek]

The power source for electromagnet is DC (either a car battery-24volts or rectified AC- upto 60V dc).
As for the wire, Iam planning to use the same wire and core used in the electromagnetic doorbell (which is a AC electromag.) but iam open to suggestions.

The permanent mag. is a bar magnet(dont know its strength or material) LxBxW=6x.5x.5cms

The distance between the two will be about 1cm (0.39 inch). As far as the switching of polarity is concerned, i have a switch for it so not a problem.

@rScotty BTW you can call me Prat. thanks for all your help.

Prat.

 

[drow13f]

I am wanting to build an electromagnet and I am wondering how the shape of the rod would effect the output.

Will a cone shaped iron core be stronger on the small end or would it be the same output per square inch as the larger end?

 

[rScotty]

I am wanting to build an electromagnet and I am wondering how the shape of the rod would effect the output.

Will a cone shaped iron core be stronger on the small end or would it be the same output per square inch as the larger end?

The best shape is a cylinder with parallel sides. Anytime that you narrow the body of the cylinder - like if you taper it - then the magnetic field lines escape out the side. Think of the induced magnetic field in the core as circulating from one pole to the other. The magnetic field wants to take the shortest path that is also low in magnetic resistance. So it doesn't want to jump through the air until it has no choice. Tapering the core would encourage the field lines to take the shorter path and those lines would be of no use to you. You want the cylindrical core to be just large enough diameter to carry the field all the way to it's end without losing any out the sides. Magnetic force in an electromagnet is a function of the number of turns of wire, the amount of current through that wire, and the magnetic resistance of the path that the magnetic field has to follow. So the more windings that the coil has, the larger diameter core that you will be able to saturate. It does help to focus the output by slightly rounding both ends of the core cylinder. Although there are some materials that will carry the magnetic field better than soft iron or common 1018 cold rolled steel, both of those are still pretty good. You don't gain much by changing the core material.
Good luck.
rScotty