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Electromagnet vs Neodymium magnet

Discussion in 'General Electronics Discussion' started by Chris Johnston, Jun 4, 2018.

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  1. Chris Johnston

    Chris Johnston

    4
    1
    Feb 17, 2016
    Is the result that you can get from an electromagnet always the same thing as a magnet that is not electro? What I mean is; I have a powerful magnet that I use to pick up metal parts, could the same thing be configured with an electromagnet. Or a better way to ask this is the magnetic field given off by an electromagnet the same exact as a non-electromaget? I do not know much about this, so any help is welcome? Not know that much about magnets I don’t know if I should mention that the non-electromagnet I am working with is neodymium. Thanks
     
  2. kellys_eye

    kellys_eye

    4,275
    1,146
    Jun 25, 2010
    Electrically produced magnetic fields are far more common than neodymium magnetic fields - and infinitely easy to control!

    Exactly the same field (flux) capabilities too - solid magnets have fixed field strengths but electro magnets have variable field strengths.

    Search for electro magnet use in scrap metal collection facilities - switching them on/off allows them to pick up 'tons' (literally) of scrap at one go and drop it where they want.
     
  3. hevans1944

    hevans1944 Hop - AC8NS

    4,543
    2,116
    Jun 21, 2012
    In general: No. The magnetic field produced by an electromagnet is temporary, and its strength is determined by the current in the electromagnet: more current produces a stronger field. No current means no magnetic field (except for a very small residual field) so, as @kellys_eye mentioned, electromagnets are used in scrap yards to pick up and move ferrous materials around, dropping their "load" when the current is turned off.

    A permanent magnet, such as a neodymium or other rare-earth magnet, or even an Alnico permanent magnet, always starts out as an un-magnetized object. After forming to the desired dimensions, it is placed between the magnetic poles of a VERY strong electromagnet. Then the current is increased until the desired field strength in the permanent magnet is produced.

    There are several different ways to "magnetize" permanent magnets, but one of the easier ways is to energize a large capacitor to several hundred volts potential and then connect it (quickly) across the magnetizing coil of the electromagnet. The resulting high-current discharge creates a strong but rapidly decaying magnetic field in the permanent magnet, causing its magnetic domains to align with the external field. More than one discharge may be necessary to obtain the strongest residual permanent magnetic field possible.

    One of the nicest things about permanent magnets is their size. They can produce a very strong magnetic field with zero power input and very little mass or volume compared to an equivalent strength electromagnet. One downside is their magnetic field is not easily turned on and off at will. Still, with a bit of ingenuity and lever mechanics, a magnetic holding fixture can be made that will release with the turn of knob... and consume zero power whether magnetically holding or free to be moved around. Machinists and optical table workers use these devices to position and hold dial indicators and lens mounts during experimental setups. More information can be found here.
     
  4. Chris Johnston

    Chris Johnston

    4
    1
    Feb 17, 2016
    Thanks so much @hevans1944, @kellys_eye, what you provide is super helpful. I will keep researching this, however, what you all provide is a great head start :)
     
    davenn likes this.
  5. skenn_ie

    skenn_ie

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    Sep 7, 2009
    Be aware: Creating a permanent magnet by discharging a capacitor: This will cause a decaying oscillation, with the inductance of the magnet and the capacitance as the resonant circuit. If using a polarised capacitor, that could kill the capacitor. Best to put a diode in the circuit to prevent a reverse voltage on the capacitor.
    Electromagnets can be considerably stronger than even Neodymium ones, but ... if the coil current goes past a certain point the core saturates so that any more current doesn't further increase the magnetic field and is just wasted energy. The saturation point depends on the core material, and it's permeability. If you drive it with AC, it is better to use a laminated core, as is used in transformers. If you use DC, it is likely that you will end up with a weak permanent magnet when the current is switched off.
     
    Last edited: Jul 3, 2018
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