The use of a relay

How to Determine if a Relay is Necessary When Connecting Signaling Products?

In the automotive sector, such as at AEB, signaling products are often connected to controllers. Depending on the parameters, it may be necessary to add a relay to safely manage the electrical load. But how do you determine if a relay is needed? In this article, we explain how to calculate this and why it is important, including the significance of using the correct wire gauge.

What is a Relay and Why is it Necessary?

A relay is an electrical component that functions as a switch. It allows you to control a high-voltage or high-current circuit with a lower voltage or current, protecting the controller from overload.

A relay is mainly used when the current (in amperes) running through the circuit exceeds the maximum capacity of the controller or wiring. Using a relay ensures the load is switched safely and prevents damage to the controller or wiring.

How to Calculate Current (Amperes)?

To determine if a relay is needed, calculate the current using the following formula:

Current (Amperes)= Power (Watts) / Voltage (Volts)​

  • Power (Watts): This is the total power of all connected signaling products.
  • Voltage (Volts): This is the supply voltage, for example, 12V or 24V, depending on the vehicle.

Example calculation

Suppose you are connecting a 60-watt LED lightbar to a 12V power supply. The current is calculated as:

Current = 60W / 12V = 5A

If the controller has a maximum current capacity of 3 A, a relay is necessary. Additionally, ensure the wiring is at least 0.75 mm² to safely handle the 5 A.

The Importance of the Correct Wire Gauge

The thickness of wires in an electrical installation determines how much current can safely flow without overheating or damaging the insulation. This is indicated by the wire cross-section (in mm²) and the maximum current (in amperes) the wire can handle.

Below is an overview of the maximum current per wire cross-section for standard copper wire:



Wire cross-section (mm²)

Maximum current (A)

0,5 

5 - 8

0,75

8 - 10

1

10 - 13

1,5

13 - 16

2,5

16 - 22

4

22 - 28

6

28 - 36






Note:

These values are estimates and may vary depending on:

  • Ambient Temperature: Higher temperatures reduce maximum current capacity.
  • Cable Insulation: Different insulation materials have varying thermal properties.
  • Cable Length: Long cables can cause voltage drops, affecting maximum current capacity.

Always consult specific standards (e.g., NEN 1010) or the manufacturer for the appropriate cable specifications in your situation.

When Should You Use a Relay?

  1. Maximum Current Capacity: Check if the current flowing through the circuit exceeds the capacity of the controller and wiring.
  2. Multiple Devices: When connecting multiple signaling products, the combined current may be too high.
  3. Safety: Use a relay to prevent wear on internal switches and overload of the wiring.

Important Considerations

  • Wire and Connector Capacity: Ensure that the wiring and connectors can handle the current.
  • Type of Relay: Choose a relay with appropriate current and voltage specifications.
  • Protection Against Voltage Spikes: Consider using a diode to protect the relay against voltage spikes during switching.

Conclusion

Using a relay and choosing the correct wiring is essential for the safe and efficient operation of signaling products. Calculate the current using Watts / Volts check the maximum capacity of the controller, and verify the wire gauge. This prevents damage and ensures the reliability of your electrical installation.

Have questions about relays or wiring? Contact the AEB team for professional advice!