Relays are essential components in various electrical systems, acting as electrically operated switches. Knowing how to check a relay is a crucial skill for anyone working with electronics, from car enthusiasts to home DIYers. This guide will walk you through different methods to test a relay, ensuring you can diagnose problems efficiently.
Understanding Relays: Types and Functions
Before diving into testing, let's briefly understand what relays are and their different types. A relay uses a small electrical current to control a much larger current, often switching high-voltage circuits. This protects sensitive electronic components.
Common types include:
- SPST (Single-Pole, Single-Throw): The simplest type, connecting one circuit to another.
- SPDT (Single-Pole, Double-Throw): Can switch a circuit to one of two different outputs.
- DPST (Double-Pole, Single-Throw): Controls two separate circuits simultaneously.
- DPDT (Double-Pole, Double-Throw): The most complex, controlling two circuits with two different outputs each.
Tools You'll Need
To effectively check a relay, you will need a few essential tools:
- Multimeter: This is the most important tool. It measures voltage, current, and resistance, allowing you to check the relay's continuity and coil resistance.
- Power Source: A suitable power source for your relay (e.g., a battery, power supply). The voltage must match your relay's specifications.
- Test Leads: These connect your multimeter to the relay's terminals.
- Schematic Diagram (if available): Understanding the relay's wiring diagram helps with identifying the correct terminals.
How to Check a Relay: Step-by-Step Guide
There are two main aspects of a relay to check: the coil and the contacts.
1. Testing the Relay Coil:
The coil is the electromagnetic component that activates the relay.
-
Measure Coil Resistance: With the multimeter set to ohms (Ω), connect the test leads to the coil terminals (usually marked 85 and 86). A reading of several ohms indicates a good coil. A reading of zero ohms means a short circuit, and an infinite reading indicates an open circuit—both are signs of a faulty coil. Consult your relay's specifications for the expected resistance range.
-
Check Coil Continuity: This test ensures the coil circuit is complete. A continuous beep from the multimeter's continuity test indicates a good coil connection.
2. Testing the Relay Contacts:
The contacts are the switching part of the relay.
-
Visual Inspection: Before using the multimeter, visually inspect the contacts for any damage like burn marks or corrosion. Clean them if necessary with a contact cleaner.
-
Continuity Test (Contacts Closed): Apply power to the relay coil (terminals 85 and 86). Using the multimeter's continuity test, check for continuity between the normally open (NO) contacts (usually marked 87 and 87a). A continuous beep indicates a proper connection.
-
Continuity Test (Contacts Open): Remove power from the coil. Check for continuity between the normally open (NO) contacts again. There should be no continuity.
-
Continuity Test (Normally Closed Contacts): Repeat the above steps for the normally closed (NC) contacts (usually marked 87 and 85). With the coil energized, there should be no continuity. When de-energized, there should be continuity.
Interpreting the Results
- Coil Test: If the coil resistance is within the expected range and shows continuity, the coil is likely good.
- Contact Test: If the contacts show continuity when expected and lack continuity when they shouldn't, the contacts are good.
Troubleshooting Common Problems
If your relay fails any of these tests, it's likely faulty and needs replacing.
Common Relay Problems:
- Stuck contacts: The contacts may be welded together, preventing switching.
- Burnt coil: Overheating can damage the coil, rendering it ineffective.
- Broken coil: An internal break in the coil wire will prevent the relay from functioning.
Remember always to prioritize safety when working with electrical components. Disconnect power before working on any electrical circuit. If unsure about any step, consult a qualified electrician.
This guide provides a detailed approach to checking a relay. By following these steps, you can effectively diagnose relay issues and maintain the smooth operation of your electrical systems. Remember to always consult your relay's specifications for accurate testing parameters.
