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Building an electromagnet, need help

  1. May 7, 2013 #1
    I've had some bad trouble trying to create an electromagnet, so I've come here in hopes of help. Basically, I need to create an electromagnet strong enough to lift 2kg of weight. Because I don't know much on the subject, I have attempted this by wrapping insulated copper wire about an iron weight. I then connect it to a 6V battery. However, it only works some of the time, and rather halfheartedly, too, as it only slightly pulls on the paper clip I test it with. So, I have to ask, does anyone have any recommendations? I have had some thoughts but nothing I test works. I'm thinking that maybe the iron weight may not be pure enough? For mathematical purposes, the wiring is 12 gauge, ten foot, insulated copper wiring, and I also do have access to higher voltages, but in my experience those can get dangerously hot.

    Thanks for any help you can give me.
  2. jcsd
  3. May 7, 2013 #2


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    How many times is the wire wrapped around the core? The more turns, the stronger the magnet.

    Poke around the internet some and you will find the equations you need to estimate the number of coils needed to get a given amount of force out of an electromagnet. I expect that you'll find that you need many more turns than you have now, and may be better off with a lot more of a lighter gauge wire. But don't make my word for it, and don't guess - a bit of calculation will tell younwhat you need to do.
  4. May 8, 2013 #3
    you have not provided the details like what kind of material you are trying to lift - is it a permanent magnet, piece of metal, or another electromagnet. as nugatory has suggested you need to poke around the internet a bit.
    from the point of view of the electrical circuit you need to figure out the internal resistance of your power supply. if this is not high enough, you may need to introduce an additional series resistance to limit the current and reduce heating. as nugatory has suggested you may need to use many more number of turns so that you can get the same magnetic field for lower value of current, thus reducing the heating, but these will in turn increase the resistance and reduce the current so you may need then to reduce the connected series resistance or switch to a higher voltage power supply. you need to play around with these numbers - voltage, resistance, and number of turns to get the right combination.
  5. May 8, 2013 #4


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    You will get better help if you describe your goal, and also what you've done (what are the dimensions of your core, for instance). Without such information, we can make a general recommendation: ditch the 12 Ga wire and replace with a zillion turns of #24 wire. You can calculate the resistance of your wire from its length, then the current and dissipated power at 6 V. You'll want to keep the power modest (maybe 10 W, depending on the number of layers in your winding).
  6. May 8, 2013 #5
    Man, if you pick up nearly 5 pounds with a 6 VDC battery not only will I be impressed I'm going to say you will not keep it suspended for very long.
  7. May 8, 2013 #6
    I do know the equations that I need to calculate this stuff with Ohm's law and the like. Sorry that I wasn't very specific about some things. Basically, I haven't been told much, but I believe that I must pick up a 2kg piece of metal, and it appears that I have been going about it all wrong. So I guess what I've gotten together from these responses is that I should change the gauge of my wire to #24 and that the number of turns is not enough. I already figured the latter, so I guess I'll have to find a much longer and larger iron core so that I can get as many turns as possible about it. Also, it appears 6V is not enough, but once again, 12V has proven dangerously hot. So, with all that I guess I'm left with two questions:

    1) Does anyone know a relation between magnetic field strength and the amount of mass it can pick up?

    2) Does anyone know how I can cool the battery down?
  8. May 8, 2013 #7
    Assuming you are charging:

    When you talk about cooling down a battery it's important to note that if you are returning a battery to charge without adequate cooling down cycles then you only serve to hyperinflate the rate of temperature rise while under load.

    Since one perpetuates the other it may be difficult to accurately estimate the primary heat catalyst (thus eliminate).

    Introduce a second cell into the experiments so that you may alternate a battery that has had adequate cooling cycles after charging. Only then may you hypothetically guage the heat encumbrance of the load (thus maximize).
  9. May 8, 2013 #8
    As of now, I am NOT using a battery that charges. I actually am using some lousy Duracells, and, though I'm not proud to say this, a car battery, which was what proved to be so hot. However, would you recommend that I DO use a charging battery? I'm guessing that if I did it could probably also have its current adjusted, which I must admit would be reasonably helpful.

    Also, I don't need help for that other question about a relation between mass and the magnetic field anymore, as I figured out what I really needed - a relation of force. As such, I figured that since F = mg (as the electromagnet will be picking up the weight from above) and F = qvB, I can substitute it so that mg = qVB, and then, of course, I can solve for B. Hopefully my work is right there.
  10. May 8, 2013 #9
    Why are you using 12 awg wire with 6 VDC?

    Are you using magnet wire?

    I wouldn't increase length as much as I would wraps. The 12 vdc car battery will increase the magnet field but so will increasing the number of turns or layers.

    Keep the turns tight.

    Doubt you should have to have a 10 long iron rod with 3 layers when using 14 awg magnet wire
  11. May 8, 2013 #10


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    The battery was getting hot because your initial coil had a low number of turns therefore low resistance
    this was producing close to short circuit condition across the battery .... yup its gonna get real hot.

    1) lots and lots of turns of the finer gauge wire as suggested, and
    2) with the many more turns you will probably be able to up the voltage of the supply

  12. May 8, 2013 #11
    That makes good sense, thank you! I guess I need to find a very long piece of iron now I suppose.
  13. May 9, 2013 #12


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    well what ever you are trying to lift will determine the shape/size of the iron core
    maybe a solid cylindrical piece of iron same diameter but half the height of a soda can

    Edit ....

    think about the size and particularly the shape of an electromagnet on the end of a crane in a scrap metal yard ... they are a BIG disc so there's plenty of surface area of core for stuff to be attracted to

  14. May 9, 2013 #13
    I was thinking that when I used an iron weight for the magnet, but it seems that I might want something more pure, so I'll probably change it out anyway. However, according to what you've said, that shape still seems to be right.
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