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What Are Power Relays and How Do They Work?


Within the realm of electronics, relays are switches that are electrically operated, capable of making and breaking contacts to manage circuits. Generally, relays are used in instances where a single circuit is to be managed by a low-power signal, or where multiple circuits are governed through a single signal. Differing in their design and capabilities, there are various switch types that may be used to benefit certain applications. Power relays are a common subtype of relay, featuring an electromagnet that allows them to open and close circuits. Capable of achieving high levels of isolation between the control signal and output, power relays find use in various applications and industries.

For a standard power relay, such devices consist of an armature, spring, one or more pairs of contacts, and an electromagnet formed from a coil and iron core. If the power relay is normally open (NO), the contacts will allow for a small amount of current to flow through the input circuit. This causes the electromagnet to be energized so that it activates, resulting in the formation of a magnetic field. As the magnetic field grows in strength, the armature will begin to be attracted, causing the contacts to move together. Once the second circuit is formed, a larger amount of current will be able to traverse the relay. To break the contacts, the power source can be removed, causing the armature to return to its resting position with the assistance of a mechanical spring. At this point, electricity will cease to move through the second circuit, and the device will turn off.

With a normally closed (NC) power relay, the opposite operation occurs as the return spring serves to maintain contacts in their closed position. When the input circuit is activated, the electromagnet will produce a magnetic field to attract the armature, causing the spring to be overpowered so that the closed contacts may be separated. At this point, current will stop flowing in the second circuit. As compared to normally open configurations, a normally closed relay will have its larger circuit powered during its resting state.

Similar to countless types of electromechanical relays, power relays only require a small amount of current to efficiently carry out their operations. Despite this, they are able to manage a much larger current than is required for their functionality. Generally, tens of milliamps are needed for opening and closing contacts, while the relay itself is able to control upwards of 10 Amps or more. As a result, power relays can optimally serve a variety of applications that exhibit higher currents.

In the past, power relays were often used to support the functionality of computer systems and telegraph systems, allowing for signals to be relayed between circuits. Nowadays, however, power relays can be relied on for numerous applications such as automotive electronic functionality, audio amplification, and telephone system operations. Within automobiles, there are countless electrical devices and systems that are provided power by a 12-volt battery. As a result, many power relays are implemented to ensure the performance of windshield wipers, the power train system, and various other assemblies. To make the replacement of such components easier, many automobile power relays are implemented within the automobile’s fuse box.

Depending on one’s needs, there are a few common types of power relays. Generally, the most popular types include electromechanical, reed, and mercury-wetted variations. With a reed power relay, a coil is wrapped around two reed switches, those of which are encased in a glass tube that is filled with an inert gas. With a mercury-wetted power relay, the reed switches are wetted with mercury, rather than featuring an inert gas. While electromechanical and reed power relays are both common, wetted-mercury types are more expensive and seldom used.

ASAP Semiconductor is a leading supplier of power relays, offering customers access to countless top-quality parts that have been sourced from thousands of leading global manufacturers that we trust. Take the time to explore our vast set of offerings at your leisure, and our team of industry experts is always ready to assist you through the purchasing process however necessary. With our RFQ service, customers can rapidly request quotes on parts that they wish to procure, and team members will provide personalized solutions in a matter of minutes. Get started today and see how ASAP Semiconductor is heralding the revolution of part procurement.


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