Applying current only to temporatrily demagnetize a magnet

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Discussion Overview

The discussion centers around the possibility of applying current to temporarily demagnetize a magnet, whether natural or man-made, rather than inducing magnetism in a non-magnet. Participants explore the implications of this approach for practical applications, particularly in the context of energy efficiency.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that it is indeed possible to temporarily demagnetize a magnet using current, suggesting that the process is straightforward and dependent on the materials involved.
  • Others argue that demagnetizing materials may require specific waveforms and that the process could leave the material unmagnetized, raising questions about the energy investment needed for re-magnetization.
  • A participant mentions the existence of door-hold magnets that operate by running DC current in opposition to the magnet to release it, highlighting practical applications of the concept.
  • Another participant suggests that the goal may be to reduce the magnetic field near the poles of the magnet rather than fully demagnetizing it.
  • One participant describes a mechanism used at their workplace that involves housing permanent magnets in a non-ferrous block, allowing for temporary disengagement of the magnetic field through mechanical means, which they argue is more cost-effective than using electromagnets.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility and methods of temporarily demagnetizing magnets, with no consensus reached on the best approach or the implications of such methods.

Contextual Notes

There are unresolved questions regarding the specific materials that can be demagnetized, the energy costs associated with re-magnetization, and the effectiveness of different methods proposed by participants.

J8675309
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Ladies & Gents,

Instead of applying current to a non-magnet to induce magnetism, is it possible to apply current only to temporarily de-magnetize a magnet (natural or man-made)?

This would seem to use up less electricity, especially since the default mode for a desktop application I'm working on is to keep a device magnetized.

Cheers,
J8675309
 
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Yes. It is as simple as it sounds.
Just like you can permanently (sort of) magnetize some materials with applied fields (like a steel screwdriver, for example), some magnets can be permanently demagnetized. This depends on the materials, some are resistant to this, others aren't.
In the power supply design world some companies marketed pre-magnetized transformer cores for single ended operation so that more dynamic energy could be stored (stored and removed at 100KHz, or so). These never really caught on because of their cost. However, it is an application of exactly what you described.
BTW, this is an easy experiment to do with a DC power supply and lots of coils of wire.
 
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DaveE said:
Yes. It is as simple as it sounds.
Just like you can permanently (sort of) magnetize some materials with applied fields (like a steel screwdriver, for example), some magnets can be permanently demagnetized. This depends on the materials, some are resistant to this, others aren't.
In the power supply design world some companies marketed pre-magnetized transformer cores for single ended operation so that more dynamic energy could be stored (stored and removed at 100KHz, or so). These never really caught on because of their cost. However, it is an application of exactly what you described.
BTW, this is an easy experiment to do with a DC power supply and lots of coils of wire.

DaveE, thanks so much. I figured it was as easy as it sounds but didn't have those materials in front of me just yet. I'll do some research on the materials to see which are the more and less resistant types. Thanks again!
 
J8675309 said:
Instead of applying current to a non-magnet to induce magnetism, is it possible to apply current only to temporarily de-magnetize a magnet (natural or man-made)?
How are you going to re-magnetize it? And don't you think that will also take an energy investment?
DaveE said:
Yes. It is as simple as it sounds.
Not sure I agree with this. Degaussing magnetized materials takes a special waveform, and again. leaves it unmagnetized.

@J8675309 -- can you say more about the application? It may be that just temporarily rotating the permanent magnet will reduce the field in your application.
 
IIRC, you can get door-hold magnets that 'fail secure'. They have a coil over the magnet, DC run in opposition to magnet to release.

There are issues such as the magnet type must tolerate such treatment, not lose its residual magnetism during working life...
'Very High Coercivity' ??
 
Presumably you don't want to demagnetise the magnet itself, just reduce the field near one of its poles to zero temporarily?
 
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At my work, we solve this problem with a very simple mechanism. Permanent magnets are housed in a non-ferrous block (looks a lot like a hockey puck), and behind the magnet is a spring that keeps the magnet pressed against the face of the puck, and a piston that can pull the magnet back, away from the face (our pistons use air cylinders). When power (air) is off, the gripper works like any permanent magnet. When the air comes on, the puck behaves just like an electromagnet that has been shut “off”. As soon as the air stops, the puck is magnetic once more.

They are a lot cheaper than electromagnets, both in up-front and operating costs, and also safer and easier to work on. As an added bonus, they help hold the tooling together when removed from the machine and sitting on a shelf.
 
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