Summary:A magnetic latching relay is an electromechanical device which can be used to control electrical cir...
A magnetic latching relay is an electromechanical device which can be used to control electrical circuits.
It consists of a coil and a movable armature that is held in place by the relay’s latch. When the coil is energized, it creates a magnetic field that moves the armature and activates or deactivates the circuit accordingly. When the coil is de-energized, the armature remains in place to maintain the current state of the circuit.
The switching action can be set up to complete or break a single circuit, or as a method of switching power between two separate circuits. Depending on the specific model of latching relay, it can be configured to operate using either a magnetic or mechanical system to achieve this actuating effect.
Generally speaking, the most popular latching relays operate in a magnetic configuration, using one or more reed switches to achieve their switching action. A brief pulse of relatively low input current is applied to the coil(s) in a latching relay switch, which briefly generates an electrical field that pushes or pulls the reed switch from one side of the coil to the other.
Once this is achieved, the relay will remain electromagnetically held in the position it was previously moved to until a further pulse of input current is required to move it back again into the opposite direction. This 'latching' effect means that a latching relay can offer a significantly lower power draw than other types of non-latching relay, as it only requires brief voltage pulses to switch from one state to the other.
Another common type of latching relay is the 'impulse switching' variant, which uses a combination of both a magnetic and mechanical system to perform this actuating effect. This can be configured to operate using a single-winding or a double-winding coil, with the difference being that the dual-coil type will require a further pulse of input current to move the relay back from its last actuated position into the opposite direction, and thus is often known as a 'double-latching' relay.
In general, the primary differences between a magnetic and a mechanical latching relay are that the former relies on an electromagnetic locking mechanism to hold the contacts in position and prevent them from being thrown open when not actuated, whereas the latter rely on a physical locking mechanism to hold the contacts in position and stop them from being thrown open once actuated.
The simplest way to test the function of a latching relay coil is by connecting it to a multimeter with a continuity mode (or buzzer mode if the meter has one) and checking that it produces a buzzer sound when a pulse of input current is passed through the coil(s). If the multimeter displays a ringing sound when you apply this current, then the relay is functional and has no issues.
A magnetic latching relay is a useful option for many applications, offering a significant benefit over other types of 'bistable' or 'keep' relays. In addition to the very low power draw compared with other relays, they also tend to be smaller and less bulky than their non-latching counterparts. Moreover, the ability to withstand repeated contact and re-connection indefinitely makes them a safe choice for use in a range of applications.