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My issue is that after the electromagnet has been switched off, the magnet and the test steel C45 object attracted to it remain attached. The residual force appears minimal, as no object which was not previously in contact can stick to the magnet, but nonetheless problematic, since the test object will not fall unless some external force is applied.

Additional details: I'm using this electromagnet.

What can I do to reduce the residual magnetism present when I switch off an electromagnet?

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    \$\begingroup\$ Can you apply a small AC current to it after switch off? \$\endgroup\$
    – winny
    Commented Jun 3, 2021 at 14:55
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    \$\begingroup\$ Demagnetization can be done by applying an alternating (Norht and South pole alternate) field of which the amplitude decays. To test that would work in your case I would use a waveform generator to generate an electrical signal for that. I would try a 1V, 50 Hz sinewave, apply that to the electromagnet, then manually decrease the amplitude slowly to the minimum. Then check if the residiual magnetism is still present. If this works then maybe an LC resonator can be made (where L is the electromagnet, C is a capacitor) to make a similar signal.... \$\endgroup\$ Commented Jun 3, 2021 at 15:03
  • \$\begingroup\$ ... then maybe simply adding a capacitor in parallel with your electromagnet could do the job. I suggest using a 1 uF non-polar capacitor and see what you get. When you apply the voltage to the electromagnet, both capacitor and magnet store energy. When you disconnect the supply, that energy will resonate between electromagnet and capacitor. But losses occur so the resonance will die out. Which is exactly what you need. Let us know if this works! \$\endgroup\$ Commented Jun 3, 2021 at 15:07
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    \$\begingroup\$ The other option is to use a softer magnetic material for your electromagnet core, but that probably isn't an option here since you're using a commercial electromagnet, not one you wound yourself. \$\endgroup\$
    – Hearth
    Commented Jun 3, 2021 at 15:19

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I would suggest two possible solutions:

First, make sure you are using a "soft" magnetic material. 1045 steel is somewhat "hard" meaning that it can be slightly permanently magnetized. Even "soft" materials may require heat treating to remove remanence. I would try a lower carbon steel like 1018 or 1010.

Second, when the steel is in direct contact with the electromagnet, the field strength inside your magnetic circuit can be very high and the field in the magnetic material may remain aligned even after power is removed, sometimes for hours. A small gap will prevent this anomaly. As a test, try a little cello tape on the object being lifted - you will lose some force but your release will happen quickly.

Good luck!

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  • \$\begingroup\$ Even though multiple answers are valid, I particularly like this "cheap and dirty" solution. Covering the magnet worked very well with simple materials like plastic foam, paper tape and printer paper. The magnetic force when the magnet is on is enough to grip well the material even with the cover. \$\endgroup\$
    – Rexcirus
    Commented Jun 4, 2021 at 23:52
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You can reduce magnetism in magnetic objects by degaussing. This usually involves running an AC or random magnetic field through the object, which can be done with a coil and alternating current.

I can't see the coil construction within the magnet but you also may be able to briefly reverse the current to remove the object.

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As others have pointed out you can try some degaussing or reversing the current flow in your electromagnet. Both solutions will be difficult to implement and you may have to deal with BOTH the electromagnet residual and the attracted object residual fields.

The force provided by your electromagnet is proportional to distance between the attracted object and the electromagnet. The holding force is maximum when there is no gap. I'm assuming here that the object you are attracting is not pulled away from the electromagnet by anything other than it's mass.

I'd suggest that you simply need to place a thin plastic sheet over the electromagnet poles to ensure there is some distance (say 0.5-2mm may be enough) between the electromagnet and the attracted object. This will ensure there is not enough residual force to keep the attracted object attached. Use an HDPE sheet which is easy to cut to fit the pole piece.

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It seems like your electromagnet is made from a material that has some residual magnetism. There is nothing that can be done about it, at least directly. You can use a reverse polarity switch, which will reverse the polarity momentarily and the attached object would then definitely fall. Try this principle first without knocking the steel object down physically but momentarily reversing the polarity. Hopefully, it works out for you.

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    \$\begingroup\$ You can degauss objects to rid residual magnetism, whether that would work on this object remains to be seen, but it can be done. \$\endgroup\$
    – Voltage Spike
    Commented Jun 3, 2021 at 15:03
  • \$\begingroup\$ Yes, you could try applying ac voltage (careful with limits though) across the terminals (degaussing), but chances are after using the electromagnet few times, the residual magnetism will come back as the magnetic domains align themselves with the magnetic field again. Quick reversal of polarity should be tried first. \$\endgroup\$ Commented Jun 3, 2021 at 15:33
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The most efficient and clean way to erase remanent magnetization is to heat the core to above its Curie temperature. But this is often impractical.

When using AC fields to demagnetize, it is very important that the current profile also has a decay term. If you only run an AC current, and then switch it off, the magnet will be stuck with whatever field direction the last AC lobe had.

One "simple" way to realize an oscillatory and decaying current is to hook up the magnet with a non-polar capacitor, charge the capacitor through the magnet, and then disconnect the voltage source and short-circuit the cap to the other coil end. If the coil has a low enough resistance (or high enough inductance), it will oscillate.

The capacitor should have a rather low capacitance ~1 uF, so it will not form a dominant RC lowpass with the series resistance of the coil.

This wont work well for very resistive magnets, as they are overdamped and won't resonate in an oscillatory fashion.

However, if your actual goal is just to release the load, a simple spacer will probably suffice.

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  • \$\begingroup\$ If the coil has a low enough resistance, it will oscillate. This will always resonate even if the series resistance is high. But with a high series resistance, the resonance might have died out before it has done one "full swing" so you might be unable to detect it ;-) \$\endgroup\$ Commented Jun 3, 2021 at 15:12

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