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What Is an Automotive Relay Used For?

What Are Relays?

Relays are electric switches that use electromagnetism to convert small, electrical stimuli into larger currents. The conversion is executed by activating electromagnets in an electrical input to form or break existing currents. Often found in circuits, relays are used to reduce the current that flows through the primary control switch. A relatively high capacity relay can be turned on and off by using a lower amperage switch, timer, or sensor.

Relays are often used when upgrading to halogen headlights on an older car. Relays help avoid the failure of a switch by reducing the strain put upon the switch. The OEM headlight switches were designed to carry less power than the current draw for halogens. If you attempt to rewire old switches to halogen headlights without the use of relays, the excess strain would lead to early failure of the OEM switches. Another necessary use of relays is when you are installing an electric cooling fan. If you directly install a cooling fan without a relay, the additional stress from the fan would be placed on the switch, resulting in early failure. Relays have proven to be effective in acting as amplifiers for electric currents.

What Is an Automotive Relay?

An automotive relay is a type of relay switch that has the ability to automate the power required to turn electrical circuits on or off at designated times. Automotive relays can switch circuits of various voltage types, and also provide the ability to power more than one circuit at the same time. Like other switches, relays are operated by electrical power, computers, or control modules. Modern electrical conveniences and safety features in vehicles are supported by switching functions provided by automotive relays. These relays provide support for cars, trucks, vans, boats, trailers, and various other vehicles and vessels. The difference between a relay and an automotive relay resides in the automotive relay’s ability to automate designated power to more than one circuit in a single relay. However, the electromagnetic assembly of both automotive and non-automotive relays allows for the preservation of functionality in switches.

How Does A Relay Work?

An electro-magnetic relay contains a soft iron core known as solenoid that is wrapped in a coil of wire. The iron core is made up of a movable iron armature, a low reluctance iron yoke, and a set of contacts. The armature is held in position by a spring, and when the relay is de-energized, an air gap is created in the magnetic circuit. The physical opening and closing of contacts is caused by this air gap. A magnetic field is generated by the coil when an electric current is delivered to the solenoid. The armature is triggered by this field, causing the contacts to move which either makes or breaks the circuit.        

Types of Automotive Relays

As vehicle applications have various requirements, there are many types of automotive relays available that meet them. Below, we have listed some of the different types.

  • Normally Open Relays

- These are the simplest types of relays. They have four pins and can only be wired to be normally open.

  • Change Over Relays

Commonly found in vehicles, change over relays have five standard pins. They can be wired to be normally closed, normally open, or with a change over configuration. This type of relay is built with two circuits rather than one, alternating the opening and closing of two circuits instead of making or breaking a single high voltage circuit. Switching from regular car headlights to high beams often necessitates the use of alternating two circuits with a change over configuration. Change over relays are also used to activate the heater or cooling system in a car.

  • Time Delay Relays

 - Time delay relays are popular and are often used to maintain and control the flow of current through their contacts. The duration of current flow can span from as little as two seconds to as long as three minutes. Time delay relays are commonly used in car parking lights, keeping the lights turned on for an extended period of time even after the passengers and driver have left the vehicle.

Advantages of Automotive Relays

Automotive relays have various functions, benefitting a myriad of applications. Some advantages of using these relays lie in their ability to switch high current circuits using low current circuits, and their capacity to activate multiple circuits using a single switch. Automotive relays can also execute logical functions and have a low price point, saving you money.


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