Latching Solenoids- Bistable ( electromechanical solenoids )

A latching or bistable solenoid incorporate a set of permanent magnets that allow the solenoid to offer hold force even after the power has been removed. The term Bistable is given to this type of solenoid because it has two stable positions. The first when the solenoid in de-energised and plunger is fully extended and second when the solenoid is de-energised and the plunger is held in position by the permanent magnets. The electromechanical force moves the solenoids from one stable position to the other depebding of the polarity of power applied. A spring can be used to move the plunger out to the extended position as the charge applied only neutralises the permanent magnet force. Solenoids can only induced electromechanical force in one direction (pulling the plunger towards the endstop). when the polarity is reversed, it has no effect on the plunger except to neutralise the magnets.

The latching solenoids series incorporate permanent magnets which provide the following benefits;
· No self heating
· Continues to hold even after the power is disconnected
· Can operate by a pulse signal
· A charge / discharge of capacitor will be enough to set and reset

Pull Operation

The action of the permanent magnets gives a small pull force with no power applied to the coil. This force increases significantly on very short strokes. The magnetic force from the coil is added to the force from the permanent magnets to increase the total pull force. The duration of the activating pulse depends on the solenoid size, stroke and / or amount of physical load. Normally 80 - 150ms is sufficient. Dialight manufacture latching solenoids to meet the needs of designers. An extensive range is available in sizes from miniature to high force, long stroke versions.

Release Operation

The force from the permanent magnets is cancelled when the coil is energised in reverse polarity, and the plunger, being free from magnetic influence is released by means of the external mechanism. In this operation, it is important to apply the correct amplitude releasing voltage. Reversing the polarity does not cause the plunger to be forced out of the solenoid! It must be removed by an external force or the mechanism which it is pulling.

Holding force of Permanent Magnets

The magnetic holding force values given for respective types are average initial values measured after application of rated voltage.