Power Relays

Power relays are switches that open and close circuits electromechanically or electromagnetically. They can control one electrical circuit by opening and closing contacts in a separate circuit. Relays typically work well in circuits with smaller currents and are ideal for low-power applications like small motors or solenoids.

Power relays are usually single-pole or double-pole units containing an armature, an electromagnetic coil, a spring and multiple contacts.

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How Does a Power Relay Work?

Although relays differ in capacities, sizes and applications, they all use the same concept to operate—one circuit powers the other. This process works depending on whether the relay is normally open (NO) or normally closed (NC).

• – Normally open relays: Normally open relays are in the open position by default, meaning that there’s no contact between the circuits when they’re not in use. When receiving power, an electromagnet pulls the first circuit into contact with the second one, closing the circuit and transmitting the power. When the power turns off, the circuit reopens to stop the flow.
• – Normally closed relays: Normally closed relays default in the closed position, resulting in a closed circuit. When the first circuit activates, the electromagnet pulls the contact away from the second circuit, keeping the larger circuit in the on-position.

Power relays differ from general-purpose relays by having the ability to handle slightly larger applications. General-purpose relays can control devices requiring 5 to 15 amps of power, while power relays can handle ranges from 10 to 50 amps and sometimes more, depending on the build and application.

What Is a Power Relay Used for?

Power relays can perform current switching for various applications, including lighting control and industrial sensors. Several specific applications include:

• – Home appliances.
• – Audio amplification.
• – Telephone systems.
• – Vending machines.
• – Gas valve control systems.

In addition, automobiles have multiple electrical systems powered by a battery, making them perfect for power relay use. Many vehicles contain dozens of relays that operate everything from windshield wipers to the horn to the windows. Automotive relays that can wear out are often found in the fuse box, allowing for accessible location and easy replacement.

Besides electromechanical relays, other power relay designs include reed relays and mercury-wetted relays. Reed power relays use coils wrapped around reed switches surrounded by gas in a glass tube to control a circuit. Mercury-wetted relays operate similarly to reed relays aside from the switches being wet with mercury. 

How to Identify a Faulty Relay

Power relays are subject to wear and eventually fail like many other electrical components. By using a multimeter, it’s relatively easy to measure the voltage where the circuits enter and exit the relay. It’s also critical to check the relay fuse or switch for mechanical defects.

A relay tester is a tool designed specifically for testing relays. Using a relay tester is straightforward, as it involves connecting the device to a power source, plugging the relay into one of the tester’s configurations and pressing the TEST button.

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Besides offering a comprehensive inventory of power relays for sale, we can also provide repair services to your company’s faulty relays. Call us today at 877-249-1701 or contact us online to learn more.

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