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HomeTips & GuidesAuto Relays – Their Applications and How They Work

Auto Relays – Their Applications and How They Work

Knowing about auto relays is very important because they play a vital role in the performance of your car systems. 

For starters, they ensure the proper functionality of components like car door locks, A/C, and side mirror tilting, among others. 

They also brighten your car headlights while preventing overheating of some car electrical components. 

Today, I will take you through auto relays, their definition, how they function, their types, and their applications.

What Is an Auto Relay?

An auto relay is an electromagnetically activated switch that controls a certain circuit in a car system. Apart from controlling a system, a relay amplifies a current to ensure the optimum functionality of high-power components.

It receives a small current which magnetizes it to close its contacts to power another device. In doing so, it ensures the control of several functions with one system, while also ensuring the longevity of inline switches.

How Does Auto Relay Work?

To understand how an automotive relay works, let’s first see its main parts. Now, if you dissect a relay, you will find a coil, a spring, and a switch with contacts.

In a normal position, the spring holds the switch open. Once you pass a current through the relay, its coil becomes an electromagnet, creating a magnetic field.

What happens is that the newly made magnet attracts the contacts and pulls the spring down. In so doing, the contacts complete a circuit, and the bigger current becomes active.

When you disconnect the relay current, the spring pulls the contacts back to their resting position, thus breaking the circuit. Therefore, you can say applying a small current on a relay, activates a much bigger current.

 A technician installing a relay

 A technician installing a relay

Types of Auto Relays

As you may expect, automotive relays appear in different types, each with its characteristics and functions. Here we look at some of the most common auto relays and how they work:

Normally open and normally closed relays

The above are the most common auto relays but can only accommodate one-way wiring. In the normally open type, you get the most common relay settings where the contact part is always open.

When you apply the current, it closes, which completes the circuit of the bigger system. Its opposite is the normally closed, which works in reverse order. That means in the default setting, the relay contact is closed.

A smaller current is applied, the spring opens, and the contact touches another current to complete its circuit.

Change over relays

Unlike the normally open and closed relays with four pins, changeovers have five pins. For this reason, you can wire them in various ways.

For example, you can make them normally open utilizing pins 30 and 87, or normally closed by pins 30 and 87a.

In addition, you can wire them as both normally closed and open (changeovers) utilizing all connection pins (30, 87, 87a). Here, the relay activates a circuit when open and another when closed.

Potten relays

Technically this relay works as any other auto relay. However, it differs from others because its bottom part features a complete epoxy sealing. While this prevents water penetration that can destroy the coil, the downside is that you cannot repair it.

Time delay relays

As their name suggests, you use these relays to maintain current flow in intervals of 2 seconds to 3 minutes. These devices feature a solid-state timer circuit with an inbuilt resistor for the time delay functionality. You can find such relays in parking lights where lights remain on for some time, even after exiting your car.

Flasher relay

In these relays, you have just three connector pins instead of the standard 4 pins. But some have four pins, although they use the fourth pin as an indicator light for knowing if the flasher is on.

Here you connect one of the pins to the power source and the other to the light you want to flash. However, note that some flasher relays act like circuit breakers but are still categorized as relays.

Thermal relays

Also known as thermal flashers, these relays function like circuit breakers. After being connected, current flows to the coil, which in turn heats it. The resulting heat is enough to deflect the contact, thus breaking or connecting the circuit.

An auto relay in different dimensions 

An auto relay in different dimensions 

Automotive Relay Application Examples

Now that you know what relays are and how they work, let’s discuss some of their applications:

Activating a higher current system

The most common application of relays in modern vehicles is switching a higher-current circuit. In this scenario, the in-line switch is too weak to handle the system’s current requirement.

For instance, a switch for connecting a high amperage lamp circuit. Using the inline switch to activate this lamp could melt or burn after exceeding its current capacity.

Therefore, you use a relay here since it can handle high currents, ensuring the switch’s durability.

Activating many circuits via one switch

The above is an application where you use a relay to activate other relays, which in turn activate several circuits. Such relays activate or deactivate several functions by switching one circuit, saving you time.

For instance, you press one button near the driver and lock/ unlock all the doors. Another example is the folding and unfolding of the side mirrors simultaneously in some car models.

Executing logical function

You can also apply the relay to operate time-controlled and momentary local functions. For example, the time delay functions of the wipers or the lighting of the interior lights.

However, while many manufacturers have programmed these activities, a relay is still an easy and cheaper alternative.

Minimizing resistance

As you may know, resistance causes the loss of electrical power and, hence, the straining of some electrical components.

The good news is that using a relay shortens the circuit, minimizing the resistance that comes with large circuits. This application is vital in brightening your vehicle headlights since the current moves efficiently.

A transparent relay

A transparent relay

Causes of Car Relay Damage

Like any other electronic device, relays can also experience damage, thus inhibiting their functionality. Here, we will discuss the two main types of coil damage:

Coil damage

As the name suggests, this is the destruction of the coil that carries the electrical current. The damage can be due to a short circuit that may cause it to break.

The short-circuiting in a coiling happens when the insulation layer peels off, making the current escape. When such damage occurs, the solution is to replace the entire relay since repairing the coil alone is complicated.

Platinum damage

Platinum damage generally results from the coil contacts experiencing a discontinuous electrical current. In addition to that, the damage can also come from a low-quality product which gets damaged easily.

A mechanic testing a relay

A mechanic testing a relay

Wrap Up

Now you know all about auto relays and their various types and applications. Note that you can install them as a cheaper option for many electrical systems in modern vehicles.

Hi I am Christa, sales manager of Cloom.

I have extensive expertise and experience in wiring harnesses and I believe I can help you.

And we have a very professional technical team who can clearly understand the customer’s needs and give professional suggestions and solutions after receiving the drawings.

If you also have wiring harness needs, please send me the drawing so that we can give you our quote and start our business.

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