The Basics of Latching Solenoids

TLX designs custom latching solenoids for a variety of applications. Click here to view specific examples of our latching solenoids.

What is a Latching Solenoid?

A latching solenoid uses an electrical current pulse or internal permanent magnet material to maintain a set position without the constant application of power. Latching solenoids (also known as bistable solenoids) have two standard positions; de-energized with the plunger fully extended and de-energized with the plunger held in position by permanent magnets.

How Does a Latching Solenoid Operate?

Electrical polarity is vital to proper latching solenoid operation. As current flows in one direction, energizing the coil field, it adds to the pull of the permanent magnet. The pull attracts the armature to the stationary pole. Once the armature is in full contact with the pole, the permanent magnet holds it in a latched position without further electrical input. Sending a current through the coil field in the opposite direction cancels the magnet’s attraction and releases the plunger from the latched position.

Types of Latching Solenoids

Permanent Magnet: These solenoids use a permanent magnet in conjunction with the solenoid coil to maintain the position of the armature. As a short pulse of electrical current is applied to the coil, the permanent magnet receives a small magnetic flux, which moves the plunger to the fixed pole. When current is removed, the permanent magnet holds the armature in the latched position.

Residual Magnetism: Internal design features in these solenoids enhances their inherent residual magnetism. This means when current is applied, the magnetism properties of the coil will hold the solenoid in the latched position. A current of reverse polarity will de-latch the solenoid until power is re-applied.

Benefits of Latching Solenoids

Latching solenoids can be turned off for most of the “on” cycle, allowing for the use of a higher current pulse. The higher current pulse produces greater speed and pull force, without the excessive power consumption or heat generation of a conventional solenoid. While holding in either the on or off position, latching solenoids use almost no power, generate almost no heat and produce almost no electrical noise.The low power consumption makes latching solenoids ideally suited for battery operated applications.

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