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Solenoid question

Permanent magnet motors put out more HP in a given volume than AC induction motors and DC motors with a wound field. So It's obvious that using permanent magnets is an advantage when it comes to size. All the solenoids with plungers that I have seen do not have a magnetized plunger. I was wondering if a magnetized plunger was used if more force could be got from a smaller package. Thanks, Eric

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Reply to
etpm
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There would be more and stronger force with magnets, and I could spare some copper windings. But the magnet would soon loose it's field due to frequent switching. No permanent magnet can withstand full field reversals for long time.

w.

Reply to
Helmut Wabnig

This was not correct. There are DC Relais which indeed use magnets for assistance. For example REED RELAIS with opener contacts. In normal condition the contacs are closed by a permanent magnet and when a DC is applied to the coil, the magnetic field is candeled and the contacts open.

Then there are bistable relais, which stay in one or the other position and a short DC pulse switches them over.

Magnets in a DC relais would reduce the force required to attract the plunger, but in non active state the plunger must be hold by a spring and secured in that position. Alltogether it would cost much more.

AC Relais cannot use a permagnet magnet for pre-loading because the field is also alternating in its polarity. A magnet would not be of any use.

w.

Reply to
Helmut Wabnig

yes, modern magnet materials are less effected by external magnetic fields. The AlNiCo magnets of old would grow weak just sitting on the shelf. Modern ceramic and neodymium magnets seem to be much more durable.

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Reply to
Jasen Betts

We use thousands of small sealed telecom-type relays, Omron and Fujitsu. Both the latching and non-latching versions have magnets inside and have polarized coils.

We're paying about $1.35 for a Fujitsu FTR-B3GA, DPDT non-latching.

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John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation
Reply to
John Larkin

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