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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[Helmut Wabnig]

On Tue, 21 Jan 2014 14:44:15 -0800, etpm@whidbey.com wrote:

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

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.

 

[Helmut Wabnig]

On Wed, 22 Jan 2014 10:36:56 +0100, Helmut Wabnig <hwabnig@.- ---
-.dotat> wrote:

On Tue, 21 Jan 2014 14:44:15 -0800, etpm@whidbey.com wrote:

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


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.

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.

 

[Jasen Betts]

On 2014-01-22, Helmut Wabnig <hwabnig@> wrote:

On Wed, 22 Jan 2014 10:36:56 +0100, Helmut Wabnig <hwabnig@.- ---
-.dotat> wrote:

On Tue, 21 Jan 2014 14:44:15 -0800, etpm@whidbey.com wrote:

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


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.


This was not correct.

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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[John Larkin]

On Wed, 22 Jan 2014 16:14:43 +0100, Helmut Wabnig <hwabnig@.- --- -.dotat>
wrote:

On Wed, 22 Jan 2014 10:36:56 +0100, Helmut Wabnig <hwabnig@.- ---
-.dotat> wrote:

On Tue, 21 Jan 2014 14:44:15 -0800, etpm@whidbey.com wrote:

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


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.

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.

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.


--

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

Precision electronic instrumentation