Electromagnet + Permanent Magnets

[DuckDodgers]

I was just wandering if you were to place permanent magnets onto the core of an electromagnet, would it have the same effect as stacking permanent magnets to increase strength?
As in if I had an electromagnet that wasnt quite strong enough, and there was no addition power available, could i just slap a magnet on it? Does it depend on the core of the electromagnet?

Just trying to satisfy a curiosity.

 

[electricpete]

If your electromagnet is powered by ac, I don't think you will find much benefit by combining it with permanent magnets.

If your electromagnet is powered by dc, it will act similar to a permanent magnet. Although I'm not sure exactly what you meant by stacking to increase strength. Certainly if you stack in a manner to reduce the final air gap between N and S you will increase strength. In any even strength of flux in air would be mmf over reluctance.

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[EdStainless]

It depends on the magnet materials, but yes it is done. I have seen devices that use a DC electromagnet to turn on and off a permanent magnet. In the off the EM polarity is opposite the PM, and the net is near zero. In the on the EM is eihter powered off, PM only, or powered in the same polarity. You must be very careful with these designs or you end up demagnetizing your PM. You nee high coercive force PM for these.

There are also designs that use very low coercive PMs as EM cores. In these you pulse the EM, it magnetizes in the desired polarity, and then provides constant field. This lets you draw low power since the EM only pulses when the field is changed. This is how one variety of the 'flipping dot' highway signs works.

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