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Making an Electromagnet — Parallax Forums

Making an Electromagnet

MicrocontrolledMicrocontrolled Posts: 2,461
edited 2010-01-17 04:04 in General Discussion
If I were to make a high powered electromagnet, what wire and what core for the spool would I need? Could I power it with a car battery charger(for the high amps)? Does anyone know enough about one to give advice on making one? Thanks in advance,

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Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2010-01-11 20:46
    You're deciding in the wrong order. You figure out how much physical room you have and how much current you have available, then you look at charts of current carrying capacity and cross sectional area of the wire. There are charts showing how many turns of a particular size wire you can fit in a particular cross sectional area. You probably want a soft iron core. Look this stuff up in the Wikipedia.
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2010-01-11 22:14
    Also depending on what you want to do with it will determine how you should orient the field and coil windings.

    A simple solenoid style or alternating N/S poles (<-- in-line or concentric rings), there are several possibilities where one may be functionally better than the other depending on the application.

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  • MicrocontrolledMicrocontrolled Posts: 2,461
    edited 2010-01-12 00:09
    I looked it up on Wikipedia and got some information on them, I am wanting it to lift a max of 200 pounds, and I know this would take over 1000 ft of wire but it is what is needed. I do not know where I will find a large iron core, though.

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  • PJAllenPJAllen Banned Posts: 5,065
    edited 2010-01-12 00:45
    stamptrol can tell you all about this.

    200 lbs.· What do you reckon the current will be?
  • Harrison.Harrison. Posts: 484
    edited 2010-01-12 01:06
    PJ Allen said...
    200 lbs. What do you reckon the current will be?
    You can lift over 200lbs using only two AA batteries: www.coolmagnetman.com/magelect.htm#Battery%20Powered%20Electromagnet. My high school physics teacher had one of these and it was pretty impressive seeing how much weight these little things could hold.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-01-12 01:09
    Here's an example of a commercial magnet that could meet your specs, depending on the nature of what you're lifting:

    ····www.electromechanicsonline.com/product.asp?pid=579

    At least this will give you some idea of typical size and power requirements for a magnet in this "weight class". Unless you're dead set on building one from scratch, you might want to haunt the surplus dealers, as they sometimes have used or overstock electromagnets for sale.

    -Phil
  • mctriviamctrivia Posts: 3,772
    edited 2010-01-12 04:07
    making electromagnets is fun and everyone should do it some times.

    Iron is the best material for a core though steel(not sergical) will work also since it has iron in it.

    The electrical code of canada states:
    14awg: 15A
    12awg: 20A
    10awg: 30A
    8awg: 45A

    I don't have my code book with me at the time so this will have to do. These are safe values ment to keep your house from burning down even if you use these loads 24/7. From experience you can easily multiply the current by 5 without causing problems to the wire for short periods of time assuming they are in an open area and not enclosed in a wall.

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  • stamptrolstamptrol Posts: 1,731
    edited 2010-01-12 15:57
    There are a thousand ways to do this, but it boils down to amp-turns in the core and your ability to get the magnet iron core intimately in contact with the 200 lbs load.

    A good iron-iron contact wastes almost no magnetic flux whereas a small air gap wastes almost all of it. An abilty to hold 200 lbs would not be a very large magnet. A magnet that can lift 200 lbs over several inches would be comparitively huge.

    The resistance per foot of wire is available and that will let you limit your current to a reasonable level for your source. Then have to have a soft iron core big enough to hold that length of wire. You know the amps and the number of turns (you counted the turns, right?) so you know the flux strength. I'm sure some manufacturer of commercial magnets has a table of lifting sizes based on flux produced.

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  • MicrocontrolledMicrocontrolled Posts: 2,461
    edited 2010-01-12 19:07
    You mean that if I wanted it to attract metal items from 3 foot away the magnet would have to be huge?

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  • mctriviamctrivia Posts: 3,772
    edited 2010-01-12 19:08
    Yes

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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-01-12 20:00
    An example of such a magnet would be the one used in an MRI scanner. And you really would not want one that powerful: www.howstuffworks.com/question698.htm.

    -Phil
  • mctriviamctrivia Posts: 3,772
    edited 2010-01-13 00:47
    No clue how expensive the stuff is but you can now buy super conductive cable. If DC power is used almost a limitless current can be used allowing for super strong small electro magnets. Unfortunately you will need liquid nitrogen to keep the magnet cold while in operation. So be careful.

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  • IRobot2IRobot2 Posts: 164
    edited 2010-01-13 17:20
    @mctrivia - I am not for sure exactly what one could do with super small/strong nitrogen cooled electromagnets but I am positive that it would be a great asset in a world domination plot... or you could at least have some tremendous fun on the weekend with it. The "be careful" should have probably been capitalized. haha

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  • mctriviamctrivia Posts: 3,772
    edited 2010-01-13 17:41
    I can think of some uses:

    The wire is 4mmx0.2mm make 1000 coils one after the next and we would have an orbital launch platfor.

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  • IRobot2IRobot2 Posts: 164
    edited 2010-01-13 17:43
    OR... the worlds biggest rail gun... tongue.gif

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  • mctriviamctrivia Posts: 3,772
    edited 2010-01-13 17:50
    That would be a powerful rail gun. In theory you should be able to get a 100g slug to near light speed

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  • IRobot2IRobot2 Posts: 164
    edited 2010-01-13 18:04
    Well I guess that would do... if it had to....

    I wonder how much power that thing would require? Is that the reason why we technically don't have one now?

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  • mctriviamctrivia Posts: 3,772
    edited 2010-01-13 18:09
    The amount of power depends on how fast you want to go. Either scenario I mentioned would require immense amounts of imaginary power but not very much real power. The power factor would be almost 0

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  • MicrocontrolledMicrocontrolled Posts: 2,461
    edited 2010-01-14 02:59
    Say I was going to make 2 electromagnets and mount them one facing up and the other facing down above the other about 4 foot away. Current considered, how much power would it take to levatate a 5 pound object inbetween the magnets assuming 12 inch currcumference iron cores holding each 1500 turns of 30 AWG magnet wire? (This is a puzzle, Ill see who can solve it)

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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-01-14 03:18
    microcontrolled said...
    This is a puzzle, Ill see who can solve it
    Does that mean you already know the answer, or that you need someone to provide you the answer? smile.gif

    -Phil
  • mctriviamctrivia Posts: 3,772
    edited 2010-01-14 03:45
    depends on what the object is made up of. If aluminum will not work so well as solid iron. Also you only need 1 magnet on the top. It needs to provide an upwards force on the object of 22.24N if you use a proximity sensor you could have a prop control the upward force to keep the object stationary.

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  • kwinnkwinn Posts: 8,697
    edited 2010-01-14 03:48
    @mctrivia Re: "The amount of power depends on how fast you want to go. Either scenario I mentioned would require immense amounts of imaginary power but not very much real power. The power factor would be almost 0"

    Hate to disagree with you but if you are going to accelerate a real mass to any velocity it will take real power. Assuming 100% efficiency and no friction or other losses E = 1/2M * V^2.
  • mctriviamctrivia Posts: 3,772
    edited 2010-01-14 04:05
    But e is made up of both real and imaginary power. A perfect inductor draws no real power.

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  • mctriviamctrivia Posts: 3,772
    edited 2010-01-14 04:08
    Sorry your right. If there was no slug then it would be imaginary. since the slug is moving that will make the power real.

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    Post Edited (mctrivia) : 1/14/2010 5:12:04 AM GMT
  • parskoparsko Posts: 501
    edited 2010-01-14 18:03
    microcontrolled said...
    Say I was going to make 2 electromagnets and mount them one facing up and the other facing down above the other about 4 foot away. Current considered, how much power would it take to levatate a 5 pound object inbetween the magnets assuming 12 inch currcumference iron cores holding each 1500 turns of 30 AWG magnet wire? (This is a puzzle, Ill see who can solve it)

    Technically, don't you want them both to face "up"? If they were opposed, then the upper would have to be WAY bigger than the lower, cause they'd be fighting one another.

    Either way, with 4 feet separating them, it's probably going to be more current than you could feasibly supply.
  • AleAle Posts: 2,363
    edited 2010-01-14 20:27
    Superconducting magnets used in magnetic resonance machines: MRI, NMR and ion-cyclotron resonance mass spectrometers are liquid helium cooled with 2 dewars one internal for He and one external for N2, the N2 has to be refilled once a week the He once every 9 months... I'd not play with such magnets. (>5 T!)

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  • mctriviamctrivia Posts: 3,772
    edited 2010-01-15 00:44
    so microcontrolled do you know the answer or do you want to know it?

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  • MicrocontrolledMicrocontrolled Posts: 2,461
    edited 2010-01-15 01:16
    We, I had a trick answer to it but now that it is brought up what WOULD it take to levetate an object in air?

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  • mctriviamctrivia Posts: 3,772
    edited 2010-01-15 01:19
    a rediculous amount of power if the magnets were that far from the object. sci-toys.com/scitoys/scitoys/magnets/calculating/calculating.html will point you in the right direction to find your answer.

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  • hinvhinv Posts: 1,255
    edited 2010-01-17 03:46
    I have heard that magnetite(in epoxy) makes a good core for an electromagnet because the particles are insulated, thus no eddy currents. Anybody had experience with this.
    BTW, magnetite can be found by just going to some open dirt driveway, sandy beach, etc, and just dragging a large magnet around. Goldbugs dispose of the stuff all of the time as it
    collects on their slooth boxes.
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