Applying current only to temporatrily demagnetize a magnet

[J8675309]

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

 

[DaveE]

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.

 

[J8675309]

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!

 

[berkeman]

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?

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.

 

[Nik_2213]

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' ??

 

[CWatters]

Presumably you don't want to demagnetise the magnet itself, just reduce the field near one of its poles to zero temporarily?

 

[LURCH]

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.