DURITE  12 Volt  25A latching changeover relay.

0-728-02   072802

 Latching relays (occasionally referred to as keep, stay, fail-safe or impulse relays) are often used to "make or break"  a circuit without the need to keep the coil energised, this gives the relay the ability to switch a circuit on and off  without continually drawing current.

The field windings on this mechanical latching relay draw no current once the initial switching operation has completed.

The operation of the relay is achieved by using a single electrical pulse across the coil terminals 30 (12V +) and S. Connect to a  MOMENTARY switch and then apply a negative pulse (or a negative pulse from an ECU or similar) this then activates the  internal field coil . The negative pulse pulls the coil in and operates a mechanical latch within the relay, this in turn holds the relay in the chosen state (i.e on or off)  The relay contacts are arranged as a SPDT (single pole double throw) arrangement. Pin 56 will connect to 56B in the off position, pin 56 then connects to 56A when energised.
These latching are ideal for use in applications where the relay is required to switch a circuit but not to draw any current after the initial switching operation has completed.