How to Choose an Automotive Relay

• Identify the Required Voltage: The first step is to confirm the voltage needed by your relay’s coil. In most automotive applications, this will be 12V or 24V, though some specialised systems may require higher ratings. Always verify the vehicle’s electrical specifications to avoid mismatch or malfunction.
• Understand the Relay Configuration: Relays are available in a range of switching formats. Choosing the correct layout depends on your system’s functional needs—whether it requires basic activation or a more complex switching path. Two of the most common are:
  • SPST (Single Pole SIngle Throw): Typically has 4 pins and is used for simple on/off switching
  • SPDT (Single Pole Double Throw): Includes 5 pins and allows switching between two outputs
• Check the Relay Footprint: Relay footprints refer to the mounting base or socket interface, which must align with your installation requirements. In certain cases, particularly for embedded systems, relays may also be mounted directly onto a PCB (Printed Circuit Board). Always refer to manufacturer diagrams or vehicle manuals when selecting the appropriate footprint. Common types include:
  • ISO Ultra Micro
  • ISO Micro 280
  • ISO Micro
  • ISO Mini
    
  • ISO Maxi

• Assess the Continuous Current Rating: This rating indicates the maximum amperage that the relay can handle on a sustained basis without overheating or degrading. Automotive relays typically fall within the 20A to 75A range. It’s essential to select a relay with a rating that meets or exceeds the electrical load of your application.
• Confirm Mounting Requirements: Relays can be installed with or without mounting brackets. Some feature integrated brackets, while others require separate fixtures. Make sure to choose a mounting option that suits your vehicle's available space and installation points.
• Choose the Appropriate Suppression Method: Suppression is key for preventing voltage spikes and protecting other sensitive electronics in the vehicle. Common suppression types include:
  • Diodes - offer quick clamping to ground
  • Resistors - dissipate excess voltage
  • No suppression - suitable only in systems where protection is handled elsewhere

Selecting an automotive relay is not just about fit, it's about compatibility, safety, and long-term reliability. Always ensure the coil voltage matches your system, the continuous current rating can handle the intended load, and the footprint suits your application.

By giving due attention to each factor, from layout and mounting to suppression, you'll improve system performance, reduce failure risk, and support smooth operation across all vehicle systems.