What is a power relay and its use within applications?

A power relay is a device that uses an electromagnet to open or close a circuit when the input (coil) is correctly excited. They provide a high level of isolation between the control signal (coil) and the output (contacts) – typically with a rated impulse voltage of 4 or 6kV.

A power relay may have change over (both normally open (NO) and normally closed (NC)) contacts or just normally open (NO) contacts. When NO contacts only are provided this usually means a greater contact gap when off can be provided, which is required in certain applications. Power relays are reliable problem solvers when it comes to switching high currents.

The basic design of a power relay utilises an electromagnet (coil and iron core), an armature, a spring and one or more pairs of contacts.

With normally open (NO) contacts a small current flows through the input circuit, activating the electromagnet. The resulting magnetic field attracts the armature which moves the contacts together, completing the second circuit, allowing a large current to flow. When the source of power is removed, the armature is no longer attracted, a spring returns it to the rest position allowing the contacts to separate, stopping the flow of electricity in the second circuit and turning off the device.

In the case of a normally closed (NC) relay, it is reversed. The return spring keeps the contacts closed. When the input circuit is activated, the electromagnet attracts the armature, this overcomes the force of the return spring and the normally closed contacts separate, stopping current flow in the second circuit. As such, NC relays keep the larger circuit in the on position by default.

In common with all electromechanical relays, a power relay uses a small electrical current (typically tens of milliamps) to operate the contacts of an electromechanical switch that control a much larger current. For a power relay, this current is usually more than 10 Amps which makes the devices suitable for applications with higher currents.

Finder’s current power relay range extends from 12 A for the miniature 56 Series power relays up to 50 A for the 67 Series high power relays. This offers a multitude of high quality, reliable options to the end-user to ensure the performance of their applications is optimal. Finder’s power relays range includes models with larger contact gaps for specific applications (e.g., industrial and domestic appliance controls, and photovoltaic). The contact gaps available are detailed on each models’ datasheet.

Finder’s power relays range also includes PCB versions for incorporation into high current electronic system applications (e.g. Electric Vehicle Charging Equipment -EVCE). Finder’s 62 series includes models with ‘Magnetic blow’ to give enhanced DC current breaking capacity.

Finder’s new Type 68.22-4300 100 A PCB mount power relay is ideal for a variety of high-power applications such as generators, UPS, pumps, photovoltaic inverters and EV chargers.