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Author Topic: DIY Electromagnets  (Read 2682 times)
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I want to build myself some electromagnets. For the coil I would use annealed copper, something like this: http://www.radioshack.com/product/index.jsp?productId=2036277

However I am trying to find some additional options for the core. I sort of like these ferrit cores: http://www.dextermag.com/products-page/b65611d0000r048-p-36x22-n48-7600-30-20.html (btw. can someone guess what unit the measurement is given in? I assume they mean inches right?)

However, I am wondering what other things, which you could find around the house, or at the doller store or wallmarts etc. might be used.

I have some of these here:
(weights for the fancy mouse I need, couse I am at the computer too much... :-/..)

Or sewing machine bobbins:

I dimly remember, that cores which consist of multiple layers are stronger than simple iron cores (google wasnt helpful here, but maybe I didnt ask the right question.). Does anyone have any other ideas for materials to use for building electromagnets? Does anyone know, or have a link to, what the proporties of the ideal core should be?

Does anyone have any tips in general on building electromagnets?

What I need are two (times 4) small electromagnets which I can switch to either attract or repuls eachother. They dont need to be able to excert a whole lot of fource, but they should be able to attract each other trough 2 sheets of regular printing paper. Ideally I would like them to be around 1cm x 1cm x 0.6cm

Cheers

P.
« Last Edit: March 07, 2011, 08:39:39 pm by fkeel » Logged


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Does anyone have any tips in general on building electromagnets?

You might look at modifying solenoids or using the internals of relays.
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Have you tried just using magnet wire (thin wire with lacquer insulation, intended for making transformers) and a 16penny nail?
Put the nail in a drill, wind a few turns by hand to get it started, then run the drill slowly as you spool the wire onto it.
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does the thickness of the core influence the strength of the magnet? for some reason I dont trust the nail solution (even though I actually just bought some for that exact reason) - Also, the ideal shape of my magnet would be just a tad smaller than a stack of 3 five cent pieces (or even like 4 ten cent pieces).

any ideas of where I can find junk solenoids? relays? ... hm. but its worth a thought...
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Don't know about solenoids, but relays in any car at the junk yard, especially the relays for the starter or the head lights.

Or cut the heads off the nails and group them all together for the diameter you want. Little epoxy to hold it all together.
Leave one long so you can wind it on the drill still.

Look at a transformer - lots of thin iron plates stacked up.
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From wikipedia:

"An electric current flowing in a wire creates a magnetic field around the wire (see drawing below). To concentrate the magnetic field of a wire, in an electromagnet the wire is wound into a coil, with many turns of wire lying side by side. The magnetic field of all the turns of wire passes through the center of the coil, creating a strong magnetic field there. A coil forming the shape of a straight tube (a helix) is called a solenoid; a solenoid that is bent into a donut shape so that the ends meet is called a toroid. Much stronger magnetic fields can be produced if a "core" of ferromagnetic material, such as soft iron, is placed inside the coil. The ferromagnetic core magnifies the magnetic field to thousands of times the strength of the field of the coil alone, due to the high magnetic permeability μ of the ferromagnetic material. This is called a ferromagnetic-core or iron-core electromagnet."

Iron is where its at!

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hehe. even if it does not appear so, i *did* check wikipedia before I posted here. I am aware that soft iron creates the strongest fields. The advantages of ferrit however are that the magnetic field dissipaits instantly when the current is turned off, while the iron will retain a magnetic charge for some time. (I guess in practice for a diy project it will seldom matter...)

however, I found very little information on what the ideal proporties of the core are. i.e. I vaguely remember from long past physics classes that different cores give different proporties ... but google didnt give much practical info on that, and my old physics book is ~8000km away from me

(the only reason I am posting here instead of actually testing, is that in theory I am studying for an exam...) I will actually test some stuff and report back :-D

Cheers

p.
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I sort of like these ferrit cores

For an electromagnet you don't want to use ferrite, you want soft iron.
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ferrit
Well especially not ferrets smiley-grin
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Ferrite can be permanently changed by over-strong magnetic fields too - its used for high-frequency transformers and some ferrites are good as permanent magnets.

Soft iron is the best (nickel and cobalt work too but more expensive and harder to work with).  If you are using AC through the winding then don't use a metal bobbin, it will carry eddy-currents and reduce the efficiency (in extremis it could heat up and melt).  Annealed pure iron is the ultimate, but as mentioned a large nail works nicely!

There are two classes of ferromagnetic materials, called 'soft' and 'hard' - the magnetically soft materials are ideal for electromagnets (they demagnetize when the current is switched off), the magnetically hard materials best for permanent magnets as they retain their magnetism.
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I sort of like these ferrit cores

For an electromagnet you don't want to use ferrite, you want soft iron.

This is what I was taught in school.
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In high school I made an AC 'motor' by winding magnet wire around a nail, then running AC thru it. The nail  was mounted horiontally. Next to it a disc with tabs sticking out (metal coffee can lid with notches cut out) was mounted with the axle perpindicular to the nail. The disc was given a spin by hand to start it, and the AC cylying on/off made it keep spinning by pulling the next tab over, then releasing, then pulling, releasing, etc.  Worked great.
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Just playing around a couple months ago I took a plain old nail and wound some 30 gauge magnet wire around it down pretty much it's full length but not perfectly packed. I'd guess it would have been around 75 to 100 windings or so, maybe a bit more. Hooked it up to 6 volts directly and got a good pull from it. Enough to lift up the end of another nail but not quite enough to pick it up completely. I'd guess if you cut it off at about 1 inch and increase the windings 2 of those would attract enough to hold a couple pieces of paper.
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ferrit
Well especially not ferrets smiley-grin

Correct, they won't stay still while you try and wind them with coils of wire unless you kill them first, but then they lose all their magnetic properties.

Lefty
 
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well, you could try ether smiley
Not sure ferrets contain any magic smoke, so not likely to work anyway smiley-cool
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