Automotive Relays

Also known as car relays, an automotive relay is an electronically-operated switch, with electro-mechanically operated switches being the most common type used in the automotive industry. Automotive relays, as the name suggests, are specifically designed to carry out a multitude of high-current applications in vehicles, including cars, vans, trucks, trailers, boats and more. These applications can vary, from operating speakers, pumps, heaters and air conditioning, and motors, etc.

What Types of Automotive Relays Are There?

Contact Configurations

The contact configuration of an automotive relay dictates how it switches electrical circuits. Choosing the correct configuration ensures the relay functions as intended within the system. Common contact configurations include:

• Single Pole Double Throw (SPDT): An SPDT relay features one common terminal that can connect to one of two other terminals. This allows for switching between two different circuits or for a single circuit to be either opened or closed in two different ways.
• Single Pole Single Throw (SPST): An SPST relay has one common terminal and one normally open (NO) or normally closed (NC) terminal. It acts as a simple on/off switch for a single circuit.
• Double Pole Double Throw (DPDT): A DPDT relay has two common terminals and can switch two separate circuits simultaneously. This provides even greater control, allowing you to switch between two different sets of circuits, offering complex switching capabilities.

Mounting Types

The mounting type of an automotive relay determines how it is physically secured within the vehicle's electrical system. Selecting the appropriate mounting style ensures the relay is stable and properly integrated. Common mounting types include:

• PCB Mount: Designed for direct soldering onto printed circuit boards (PCBs), PCB mount relays are typically compact and used in lower-current applications, often involving 10 Amps or lower.
• Flange Mount: Flange mount relays feature a flange with mounting holes, allowing them to be securely attached to a surface using screws or bolts. This provides a robust and stable mounting solution, especially in applications subject to vibration.
• Plug-In: Plug-in relays are designed to be easily inserted into a corresponding socket. This configuration simplifies installation and replacement, making maintenance and troubleshooting more convenient.

Terminal Types

The terminal type of an automotive relay dictates how electrical connections are made to the relay. Choosing the correct terminal type ensures secure and reliable electrical connections within the vehicle's wiring harness. Common terminal types include:

• PCB: PCB terminals are designed for direct soldering onto printed circuit boards, providing a compact and secure connection in electronic circuits.
• Quick Connect: Quick connect terminals, often spade or Faston terminals, allow for fast and easy connections using crimped connectors. This type of terminal is commonly used in automotive applications where quick installation and removal are required.
• Through Hole: Through-hole terminals feature pins that are inserted through holes in a PCB and then soldered on the opposite side. This provides a strong and reliable mechanical and electrical connection.

Common Automotive Relay Voltage

Automotive relays are commonly available in various voltage ratings to match different vehicle electrical systems. However, the 12V auto relay is the most prevalent due to the widespread use of 12V systems in most cars, vans, and smaller trucks. In both 4-pin and 5-pin configurations, two of these pins are dedicated to the internal coil, facilitating the passage of the typical 12V required for operation. This 12V current then energises the internal switch mechanism within the relay, enabling it to control the high-current circuit.

Automotive Relay Installation Best Practices

Proper installation of automotive relays is crucial for ensuring their reliable operation and preventing premature failure. Following these best practices will help maximise the lifespan and performance of your relays:

• Employ proper mounting techniques to minimise vibration damage, ensuring the relay is securely fastened to a stable surface to prevent excessive movement that can lead to internal component wear or connection issues.
• Adhere to correct wiring procedures, including accurate terminal identification, carefully referencing wiring diagrams to ensure each wire is connected to the appropriate terminal to prevent short circuits or improper operation.
• Consider heat management in engine bay installations, mounting relays away from direct heat sources or utilising heat shields where necessary, as excessive heat can degrade relay components and reduce their lifespan.
• Utilise relay socket and connector options for easy maintenance, opting for plug-in sockets that allow for quick and simple relay replacement without the need for rewiring.
• Observe any relay orientation requirements specified by the manufacturer for optimal performance, as some relays may be designed to operate best in a particular mounting orientation.

Troubleshooting Common Car Relay Issues

Identifying and addressing relay problems promptly is essential for maintaining the functionality of vehicle systems.

• Identifying Symptoms of Relay Failure: Common symptoms of a failing relay include malfunctioning lights, inoperative fuel pumps, non-responsive starters, or intermittent operation of various electrical components.
• Testing Procedures: Use a multimeter or circuit tester to check for proper voltage at the relay coil and the presence of continuity across the relay contacts when activated.
• Diagnosing Intermittent Relay Problems: Intermittent relay problems can be challenging to diagnose. Carefully inspect the relay for loose connections, corrosion, or signs of overheating, which can cause erratic behaviour.
• When to Replace vs. Repair Relay Circuits: In most cases, relays are inexpensive and easily replaceable. However, if the problem lies within the wiring harness or the control circuit, those components may require repair or replacement.

Avoid Common Mistakes when Purchasing Automotive Relays

• Don't Ignore Coil Voltage: Using a 24V relay in a 12V system (or vice versa) will lead to operational failures. Always match the relay coil voltage to your vehicle's electrical system.
• Don't Overlook Socket Compatibility: Not all relay sockets are universally compatible. Ensure your replacement relay matches the original's pin configuration or that you're replacing both the relay and socket together.

Applications of Automotive Relays

While primarily designed for vehicles, the robust and versatile nature of automotive relays has led to their adoption in various other industries where reliable switching of high-current loads with low-current control signals is required.

• Transportation and Logistics: Automotive relays are crucial in various transportation and logistics applications. They’re used in trucks, buses, trailers, and even boats to control lighting systems, auxiliary power units, pumps for fluid transfer, and various other electrical functions. Their durability and ability to withstand vibrations make them suitable for these demanding environments.
• Industrial Automation: In industrial automation, automotive relays find use in controlling motors, solenoids, and other high-power components in machinery and automated systems. Their reliability and cost-effectiveness make them a viable option for simpler switching applications where a rugged switch is needed.
• Renewable Energy Systems: Automotive relays are increasingly being integrated into renewable energy systems, particularly in off-grid solar and wind power setups. They can be used to control the flow of power to and from batteries, manage loads, and switch between different power sources. Their 12V and 24V compatibility aligns well with common battery voltages in these systems.
• Specialty Vehicles and Equipment: A wide range of specialty vehicles and equipment, such as agricultural machinery, construction vehicles, and emergency service vehicles, utilise auto relays. They control various functions specific to these applications, including work lights, hydraulic pumps, and signalling systems. Their availability and relatively low cost make them a practical choice for manufacturers.

Your Trusted Automotive Relays Supplier and Manufacturer

RS Australia is a trusted and widely used supplier of auto relays, offering a comprehensive selection to meet the diverse needs of the Australian automotive industry. We stock high-quality automotive relays from leading manufacturers, including TE Connectivity, Panasonic, and Durakool, ensuring you have access to reliable and durable components.

Beyond automotive relays, RS Australia also provides a wide range of other relay types, including power relays and timer relays, catering to various electrical control applications.

Browse our extensive selection of automotive relays today. For more information regarding delivery options, please refer to our Delivery Policy.