-=> Mike Ross said to Jasen Betts
 -=> about "{at}%^{at}#$%^ VEROBOARD" on 03-16-04  09:00.....

 MR> Yes a "holding current" rating. It's due to a mechanical
inertia that
 MR> the relay motor works against to both turn on and then to turn off.

That explanation may be one point of view but it is greatly
missleading. There isn't any motor as such to operate the relay,
and there definitely isn't any motor to release it - unless you
class a spring as a motor.

The way it works is this, if you'll pardon me for being a bit
wordy.

The solenoid exerts a magnetic force to pull the armature in
against a spring to operate the relay. As the armature gets
closer to the pole of the solenoid, the airgap in the magnetic
circuit gets shorter and the magnetic attraction gets stronger,
so the relay snaps in for the last part of its travel.

To release the relay, the current in the solenoid is reduced
below the holding current and the spring will then pull the
armature away from the pole piece of the solenoid. As the
armature starts to move away, and the air gap increases, the
magnetic attraction weakens and the spring pulls the armature
away faster and faster, to give a snap off effect.

The reason why the current level above which the relay will
operate (turn on) is so much higher than the current below which
it will release (turn off) is that the pullin current has to
generate enough magnetic attraction to pull in the armature from
over a wide air gap. The holding current just has to generate
enough magnetic attraction to hold the armature in over a much
narrower air gap.

   ,-./\
  /     \ From Greg Mayman, in beautiful Adelaide, South Australia
  \_,-*_/    "Queen City of The South"    34:55 S  138:36 E
       v

... I've got a very bad feeling about this.
___ Blue Wave/386 v2.30

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