How to Test a Relay?

How to Test a Relay? . Relays are critical components in electrical systems, acting as switches to control circuits. Testing them ensures smooth functionality and prevents costly failures. Let’s dive into the details of how to test a relay, including the tools you need, safety tips, and expert techniques.

What is a Relay?

A relay is an electromechanical or solid-state switch that controls electrical circuits by opening and closing contacts in response to an electrical signal. Relays are widely used in:

• Automotive systems: Ignition, fuel pumps, and lights.
• Industrial machines: Motor controls and automated systems.
• Residential devices: HVAC systems and security systems.

Read More : Relay vs. Circuit Breaker: 7 Key Differences You Must Know

Types of relays include:

1. Electromechanical Relays (EMRs): Traditional designs with mechanical components.
2. Solid-State Relays (SSRs): No moving parts, offering faster switching.
3. Time-Delay Relays: Operate with a predefined delay.

Tools Needed for Relay Testing

Before testing, gather the following tools:

1. Multimeter: For checking resistance and continuity.
2. Relay Tester: A specialized tool for quick diagnostics.
3. Jumper Wires: Useful for bypassing or energizing circuits.
4. Power Supply: To simulate the relay’s working environment.

Read More : How to Wire 8-PIN Relay for Holding or Latching Circuit?

How to Test a Relay, Step by Step

Step 1: Understanding How a Relay Works

Before we get into how to test a relay, we should understand how it works. There are multiple types of relays, but in this guide, we’ll focus on the operation of a typical four-pin relay that is configured as a normally open Single-Pole Single-Throw (SPST).

These relays consist of four pins typically labeled 85, 86, 87, and 30. Pins 85 and 86, located across from one another, are for the electromagnetic coil. Pins 87 and 30 are for the switched circuit. When you energize the electromagnetic coil circuit, it closes a switch between pins 87 and 30 and allows power to pass through the relay and to whatever is powered on the other side (for example, your headlights or a cooling fan).

Read More : What Are The Types of Relays?

The actual DIN 72552 standard defines each pin as follows:

• 30: From battery +
• 85: Relay coil –
• 86: Relay coil +
• 87: Common contact
  • 87a: Normally-closed contact
  • 87b: Normally-open contact

Step 2: Locate the Relay

So you’ve scoured the internet and determined that you need to test a relay. Well, the next step is actually finding that relay, and depending on what it controls, it could be just about anywhere—under the hood, in the fuse box, under the dash, or elsewhere. We recommend consulting a vehicle-specific repair manual to determine the location. It may also be found in a wiring diagram of your vehicle.

Step 3: Swap Out the Relay

The easiest way to test a relay is to simply swap it out with a known-good part. Relays are often cheap, but having one on hand isn’t always going to happen. Watch out, though—whatever it was that cooked your first relay can do exactly that to your second one if the root of the problem isn’t fixed.

Read More : How to Reverse Operation of Photo Eye for Motor Using Relay?

Step 4: Measure the Resistance

It’s time to break out your multimeter. You can prepare to test your relay in the car, or put it on a test bench like us. Either way, be sure to de-energize your relay by removing power to it before you get to work.

Next, you’ll set your multimeter to measure resistance by switching it to read ohms. You will want to measure the resistance between your electromagnetic coils, which is a Normally Closed (NC) circuit. On a four or five-pin relay, these are pins 85 and 86.

If you get a measurement between 50 and 120 ohms, the coil is likely good. Anything out-of-spec means that the coil winding is bad and you’ll need a new relay.

Read More : How to Control a Three-Phase Motor Using Solid-State Relay?

Step 5: Test Switch Pin Continuity

Now that we know that your coil is good, we’ll want to test the switch pins. These pins are a Normally Open (NO) circuit, meaning that they are open by default and have no continuity. There should be no load traveling through it until the circuit is closed by energizing the relay.

To test this, leave your multimeter on the ohms setting and measure the resistance between the switch pins. On a four-pin relay, these are typically labeled 87 and 30. You should see no resistance at all between these pins. If you do, that means that the pins are stuck closed and the relay is bad.

Step 6: Test the Energized Relay

Since we’ve verified that your relay is in working order when not powered, it’s time to see what happens when we add a bit of electricity to the mix. We’re going to be using a simple benchtop power supply to test our relay, but you can use a 9-volt battery or the 12-volt power coming from your car.

Energize the coil pins (again, these are typically 85 and 86 on a 4-pin relay). You should hear an audible click as the electromagnetic coil is energized and the internal switch closes.

Read More : What is a Relay Protection Tester?

You will now set your multimeter on its continuity setting. This setting typically gives an audible beep when a circuit has continuity, and because you’re handling an energized circuit, it’s easier to keep your eyes on the relay and your ears listening for the beep.

Since you energized the coil pins, the NO circuit between the switch pins (87 and 30 on a four-pin relay) is now closed. You can take each probe on the multimeter and touch either corresponding switch pins and you should hear a beep to indicate continuity between the pins.

If you don’t hear a beep, your switch pins are stuck open and the relay is bad.

Step 7: Test the Voltage

Just because your relay’s switching function works doesn’t mean that it’s good. You’ll still want to test that your relay is delivering the correct voltage on the switched end to account for corroded or bad contact points.

Set your multimeter to DC volts and ensure you know the supply voltage. If using a benchtop power supply, you should see this on the power supply itself. If using your car’s battery, measure the voltage across the terminals. A non-running car’s battery should measure very close to 12 volts.

Read More : Why Are There Different Types of Relay Protection in Power Systems?

Next, with your relay energized and power supplied to one side of the switch pins, measure the voltage on the switch pin without any wires going to it. This should read close, if not identical, to the supply voltage. If it doesn’t, replace the relay.

Safety Precautions

When testing relays, safety is paramount. Here’s how to stay safe:

• Always disconnect power before handling relays.
• Use insulated tools to avoid accidental short circuits.
• Wear safety goggles and gloves when working with high-voltage systems.
• Verify tools are in good condition and calibrated.

Signs of a Faulty Relay

Faulty relays can exhibit these symptoms:

• Inconsistent operation of connected devices (e.g., lights flickering).
• No clicking sound when energized.
• Burnt or corroded terminals.
• Overheating or a burnt smell near the relay.

Common Issues During Relay Testing

When testing relays, you might encounter:

• False Negatives: Misdiagnosing a working relay as faulty due to poor connections.
• Tool Malfunctions: Using an uncalibrated multimeter can yield incorrect results.
• Environmental Factors: Dust or corrosion affecting terminal contact.

Read More : Power Supply Devices And Systems Of Relay Protection

Applications of Relay Testing

Relay testing is crucial in:

• Automotive Diagnostics: Ensuring vehicle reliability.
• Industrial Maintenance: Preventing equipment downtime.
• Home Electrical Systems: Maintaining HVAC and security system efficiency.

FAQs on How to Test a Relay

Q1: What happens if a relay is faulty?
A faulty relay disrupts the electrical circuit, causing connected devices to fail.

Q2: Can a relay be repaired?
In most cases, it’s more practical to replace a damaged relay than repair it.

Q3: How often should I test relays?
Test relays during routine maintenance or if you notice device malfunctions.

Related Topics

• Relay vs. Circuit Breaker: 7 Key Differences You Must Know

• How to Wire 8-PIN Relay for Holding or Latching Circuit?

• What Are The Types of Relays?

• How to Reverse Operation of Photo Eye for Motor Using Relay?

• How to Control a Three-Phase Motor Using Solid-State Relay?

• What is a Relay Protection Tester? Essential Guide for Power System Reliability & Safety

• Why Are There Different Types of Relay Protection in Power Systems?

• Why Relays Are Essential for Power System Protection: Uncover the 7 Key Reasons

• Power Supply Devices And Systems Of Relay Protection