motorrelay

Motor relay is a device used to control electric motors by opening or closing their power circuits. It provides electrical isolation between control electronics and the motor, enabling remote, automated, or timed operation. In practice, motor relays come as electromechanical relays (EMRs) and, less commonly, as solid-state relays (SSRs) designed to handle inductive motor loads.

An EMR uses an electromagnet to move one or more contacts. When the coil is energized, contacts close (or switch) to connect power to the motor; de-energizing the coil reopens the circuit. Relays are rated by coil voltage and resistance, and by the current and voltage their contacts can carry, with derating for inductive loads. Configurations include SPST, SPDT, and DPDT; DPDT relays can be wired to reverse polarity for simple bidirectional DC motors. SSRs can switch motors without mechanical wear, but they generate heat and may have voltage drop considerations.

Motor relays must account for inductive kick and inrush, so flyback protection on DC coils and, where appropriate, snubbers across contacts or the motor are common. For DC motors, a typical reversing setup uses two DPDT relays or a single DPDT arrangement with correct wiring. For AC motors, relays must be rated for the motor’s voltage and current and for AC switching.

Applications include automation, robotics, door and gate controls, and automotive accessories. In control systems, relays are driven from microcontrollers via drivers and flyback protections. Solid-state relays offer quiet operation and long life, but may require heat sinking for high-current motors.