Power relays are reliable problem-solvers for high current switches. In this article, we will introduce power relays in detail.
What is a power relay?
A power relay is a device that uses an electromagnet to turn a circuit on or off when the input (coil) is excited correctly. They provide a high level of isolation between the control signal (coil) and the output (contact) -- typically rated at 4 or 6kV impulse voltage.
A power relay is a switch that turns a circuit on or off with an electromagnet. The basic design of a relay uses an electromagnet coil, an armature, a spring, and one or more contacts. If the power relay is designed to be normally on, the circuit is incomplete in the off state.
When the power supply is applied to the power relay, the electromagnet attracts the armature, which is a movable arm made of iron. The spring-supported armature is pulled in the direction of the coil until the coil touches the contact, closing the circuit. If the relay closes correctly, the coil pulls the armature away from the contact and the circuit is disconnected.
A power relay may have switched (normally open (NO) and normally closed (NC) contacts, or just normally open (NO) contacts. When only NO contacts are provided, this usually means that a larger contact gap can be provided during disconnection, which is required in some applications. Power relays are a reliable solution to problems when it comes to switching large currents.
How does the power relay work?
The basic design of a power relay uses an electromagnet (coil and core), an armature, a spring, and one or more pairs of contacts.
At the normally open (NO) contact, a small current flows through the input circuit, activating the electromagnet. The resulting magnetic field attracts the armature, which drives the contacts together to complete the second circuit, generating a large current. When the power supply is removed and the armature is no longer attracted, the spring returns the armature to its resting position, allowing the contacts to separate, stopping the current in the second loop and shutting down the device.
In the case of a normally closed (NC) relay, it is reversed. A return spring keeps the contact closed. When the input circuit is activated, the electromagnet attracts the armature, which overcomes the force of the reset spring, separating the normally closed contacts and stopping the current in the second circuit. Therefore, the NC relay defaults on the larger circuit.
What is a power relay used for?
Like all electromechanical relays, electric relays use a small current (typically tens of milliamps) to operate electromechanical switch contacts that control a large current. For power relays, this current typically exceeds 10 amperes, making the device suitable for higher current applications.
Power relays can operate at low voltages, but also at high voltages. Therefore, power relays are used in many different applications, including audio amplification, automotive electronics, and telephone systems. Power relays were also used in early computer and telegraph systems to carry signals from one line to another.
Cars contain many electronics and systems, all powered by 12-volt batteries, making power relays ideal for use in cars. Many cars contain 20 or more relays that control everything from the horn to the powertrain and windshield wipers. While relays in cars can be installed throughout the vehicle, the most easily worn and easily replaced are often fuse boxes. This position facilitates positioning and replacement of the required power relays.
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