Automotive Electrical Relay

Automotive Electrical Relays – How They Work

Jump to:
1. What the Electrical Relay Does
2. How It Works – Step by Step
3. Key Components Involved
4. Common Misconceptions
5. Why This Matters

Anchor 1

An automotive electrical relay is a switch that allows a small electrical current to control a much larger current. This makes it possible to operate high-power electrical circuits using low-power control switches.

Relays are widely used in vehicles to control circuits such as lighting, motors, and other high-current electrical loads.

This page explains what an electrical relay does, how it operates internally, and where different relay types are commonly used in vehicles.

How it Works - Step by Step

Anchor 2

Control current applied
A small electrical current is supplied to the relay’s control circuit.
Electromagnet energised
The control current energises an electromagnet inside the relay.
Armature movement
The magnetic field attracts an armature, causing it to move.
Contact operation
As the armature moves, it opens or closes electrical contacts inside the relay.
Load circuit switched
The contacts allow a separate, higher-current circuit to be switched on or off.
Relay de-energised
When the control current is removed, the electromagnet de-energises and the contacts return to their rest position.

Key Components Involved

Anchor 3

Electromagnet (coil)
Creates a magnetic field when energised by the control current.
Armature
A movable metal component attracted by the electromagnet.
Contact points
Open or close to control the high-current circuit.
Normally open contact
Open when the relay is at rest and closed when energised.
Normally closed contact
Closed when the relay is at rest and opened when energised.

Common Misconceptions

Anchor 4

Relays amplify electrical power
Relays do not increase power; they switch one circuit using another.
All relays operate the same way
While the basic principle is the same, relays can have different contact arrangements.
Relays are only used for lighting
Relays are used throughout vehicle electrical systems wherever higher currents need to be controlled.

Why This Matters

Anchor 5

Understanding how electrical relays work explains how vehicles safely control high-current circuits using low-current switches. This is fundamental to understanding modern automotive electrical and electronic systems.

It also provides a foundation for understanding more complex electrical control strategies used in vehicles.

Quick Reference

System: Electrical & electronic systems
Component: Electrical relay
Primary Function: Switch high-current circuits using a low-current control
Common type: Normally open and changeover relays