Motor or solenoid without permanent magnets

Discussion in 'General Electronics Chat' started by henradrie, Feb 16, 2016.

  1. henradrie

    Thread Starter New Member

    Feb 16, 2016
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    I'm trying to find a small motor or solenoid that does not have permanent magnets. I've searched for a while but can't find anything even though I'm sure it exists.

    Does anybody know where I could find such things?

    The solenoid or motor will be used next to a magnetometer so it can't have any permanent magnets affecting the measurements.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Any induction motor does not have P.M.'s. You will have a hard time finding a DC motor with wound fields these days.
    Most solenoids are wound, not PM.
    Max.
     
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    @henradrie, Why would a permanent magnet be any different than the magnetic fields in a wound motor?
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    As sortbus said, a magnetic field is a magnetic field whether it is from a PM or an electromagnet. Are you sure a PM-Free motor will solve your problem?
     
  5. henradrie

    Thread Starter New Member

    Feb 16, 2016
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    Because when a wound motor is turned off the magnetic field disappears and the magnetometer can get its reading. A permanent magnet is always on and will prevent the magnetometer from getting an accurate reading.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Even without PMs, a motor is likely to have some magnetic remanence. Most steel objects are likely to be weak magnets too.
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    As long as they are not moving relative to the magnetometer will not cut through any magnetic lines of flux. A stationary metal object (or even magnetic object) should not be a problem. I interested in the details.
     
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  8. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Aren't Universal motors "Wound rotor"?
     
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  9. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    But I too agree, the large mass of electric steel will behave like a weak magnet even with power off. I suggest you look into hydraulic or air, there may be non magnetic types in those forms
     
  10. crutschow

    Expert

    Mar 14, 2008
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    Magnetometers measure static fields.
    No movement needed to measure the field.
     
  11. henradrie

    Thread Starter New Member

    Feb 16, 2016
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    Thanks guys,

    I found some solenoids that should work for my application. Even though there will still be some magnetic effects after the coil is turned off they are more manageable than permanent magnets. This should allow us to get accurate measurements of the earth's magnetic field even though we have to compensate.

    The solenoids will be mounted on an instrument that goes underground with only one cable connecting it to the surface. All power and communication must be through this single cable. As much as I want to use air that isn't an option.
     
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