choosing a permanent magnet

Discussion in 'Off-Topic' started by samjesse, Feb 15, 2010.

  1. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    Hi

    I have a U shape metal core and want to buy a permanent magnet which I can place between the core's ends "thus completing the flux path through the core". the permanent magnet must not saturate the core, I also have the H-B curve fore the core material.

    In the H-B curve, the point at which the material becomes saturated is at 1 "Magnetizing Force-H-Oersteds"

    Do I look for a permanent magnet which has less than 1 Magnetizing Force in H-Oersteds? well, they are rated by their energy products number MGOe as in here.
    The second thing, I thought the volume of the material in the core must effect the saturation, i.e. the more the volume the more magnetizing force it will need before it gets saturated, well how come the H-B curve does not show this?

    Please help me understand those issues.

    thx
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Last edited: Feb 15, 2010
  3. Duane P Wetick

    Active Member

    Apr 23, 2009
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    The magnetic force figure (strength of material) is un-related to the volume of the stuff. Thats why there is no strength/ volume figure and also why there is and has been a world-wide effort to develop new and cheaper high strength magnets; ie smaller PM motor packages (cars), etc.

    Cheers, DPW [ Everything has limitations...and I hate limitations.]
     
  4. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    That is an interesting link. I will take a closer look when I have more free time.
    I wounder why he is not selling them, maybe the output Hz will not run a house refrigerator.

    Thx
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Most of the stuff is old news, dated around 2001. Yet to read it it is only up until the author starts his business. I suspect the business is up and running myself.
     
  6. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    what things are to be considered when buying a permanent magnet in regards to avoiding the saturation of a core, given the H-B for the core is known?
     
  7. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Thomas Beardon is a world-class crackpot.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    It would be helpful to know the purpose of this application. So far, it sounds like another perpetual motion device.
     
  9. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    I am trying to make a tool hanger by extending a long metal U shape bar across a 4 meter wall. instead of buying a 4 meter magnet, why not use a much smaller one and let the flux path activate the rest of the "core". then I have my good and cheap magnetic tool hanger.
     
  10. retched

    AAC Fanatic!

    Dec 5, 2009
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    You may be over thinking it. You could use 2 magnets, one at each end, just make sure they are rated for the pull strength needed to hold the tools + rack
     
  11. Duane P Wetick

    Active Member

    Apr 23, 2009
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    You have to consider whether or not you want your tools to become magnetized (residual magnetism) by hanging on the rack. Don't forget, they pick up all the filings lying around your shop and that can be a real nuisance. An AC coil run from a powerstat can serve as a proper de-magnetizer; varying the AC controls the de-magnetizing characteristics.
    If you want a proper magnetic tool holder, select some small blocks of ceramic C5 material and add two 1/8 mild steel bars on each side and epoxy them in place using a rigid wood form.

    Cheers, DPW [ Everything has limitations...and I hate limitations.]
     
  12. samjesse

    Thread Starter Active Member

    Sep 14, 2008
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    Lets take this more technically.
    If the tool rack is a big steel bar, how do I select the correct permanent magnet for it? Does size mater?

    OK. lets try it another way.
    If I have a 5 meters steel rod with a square cross section 1 meter width.
    How much magnetizing force is needed to saturate it magnetically?
    can I bring a rare earth tiny "finger nail" size permanent magnet and expect it to work? there must be a formula that accounts for size.
     
    Last edited: Feb 19, 2010
  13. retched

    AAC Fanatic!

    Dec 5, 2009
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    Magnetizing the rod wouldn't be done by placing a magnet on an end. You would have to 'rub' the magnet across the bar in the same direction repeatedly to line up the particles. Just sticking a magnet on the end will have little effect on the bar as a whole, however, it will reduce the effectiveness of the magnet to the wall.
     
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