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I am trying to design an electro magnet with a large surface area at the end. The first design used a 1/4" rod wound with magnet wire resulting in about 10 ohms of resistance driven with 12 V. This produced a fairly strong magnet with a small area at the end. My desire is to create a magnet of similar strength but with more surface area at the end to allow for easier location with another magnet. So I soldiered a 1"x1" plate of approximately 1/8" thickness to the end of the 1/4" rod thinking that the flux would then spread out over the area. It turns out that the magnet has very weak magnetism on the surface but is strong around the edges so I think that the plate is directing the flux to turn and flow out of the edges (not the desired effect). I know that I could just increase the diameter of the rod to say 1" but this will cause the magnet to weigh more and reduce the number of turns. It there a way to couple the small diameter core (i.e. to get more turns) and spread out the flux at the end over a wider area without the flux being drawn to the edges?

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Even you are not specify the holding or attracting “strength” of your electromagnet, increasing the area of your pole tip, you spread the flux and increase the leakage. Usually conical, or sharp pole tips design resulting a flux density gain especially in short distances. You can see this in magnetic tweezers.

enter image description here

The pole tip of your core also highly related with the dimensions of the object you are going to lift, because the ferromagnetic object acts as a mirror of your electromagnet core. If your core tip area is much larger than your object, then it will shift to the edge of the core. Good performance starts with an analogy of 0.8:1.
In your case you can construct a “jacketed” electromagnet in case of a holding electromagnet desired, or try to make the coil longer (longer core) increasing the magnetic lines return path and strengthen the attractive force.

So I think the answer is no.

EDIT The traction force of the electromagnet will be

enter image description here

where P is pull in Kgr, Ag the cross sectional area of gap, lg the length of the air gap in cm, and NI is the ampere-tirns. (Charles R. Underhill "Solenoids Electromagnets and Electromagnetic Windings" 2nd edition NY 1914)

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  • \$\begingroup\$ Thank you for the answer. I am trying to create two magnets which will attract each other when close. Increasing the area seemed to be the best way to do that. If a conical design is used, will it improve the proximity performance? \$\endgroup\$ – Commodore63 Apr 14 '14 at 3:49
  • \$\begingroup\$ I did some FEM modeling and it seems like the lines of flux are leaking out of the sides of the cone. \$\endgroup\$ – Commodore63 Apr 14 '14 at 4:08
  • \$\begingroup\$ @Commodore63 1- If you want a polarized electromagnet, use a combination of electromagnet and permanent magnet. 2- Try to model the conical shape, using angles between 40-55 deg. and keep the conical length part less than a quarter of core diameter. \$\endgroup\$ – GR Tech Apr 14 '14 at 4:31
  • \$\begingroup\$ Would there be any advantage to using a horseshoe configuration or "C" configuration as opposed to a bar? \$\endgroup\$ – Commodore63 Apr 15 '14 at 1:24
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    \$\begingroup\$ @Commodore63 Horseshoe supports lifting force by design i.e close magnetic circuit through armature. \$\endgroup\$ – GR Tech Apr 15 '14 at 4:52

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