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Leif Neland

:
I work on commercial fire alarm systems mostly in apartment houses. Many of
these buildings in the common hallways employ electromagnetic units mounted
on the walls and an iron disk on the back corner of the doors. When the doors
are opened and the disks are mated with the electromagnet the doors are held
open in place. These doors all have pneumatic closers on them as well which
are always applying a force in the opposite direction to try to close the
door.

When the alarm is activated the 24VDC is removed from the coils and the doors
are supposed to be automatically pulled closed by the force of the pneumatic
unit.

Would it be possible to feed the electromagnets with 24V AC?

That should prevent the doors to get permanently magnetized.
I don't know if that'll make the doors/magnets hum though.

Leif

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