How To Test a Solid State Relay? 3 Easy Methods

A Solid State Relay, or SSR, is like a smart switch. It's a part we use in electronics to control the flow of electricity without any moving pieces. Unlike regular switches that click on and off, SSRs use tiny electronic parts to do the job. They're quiet, fast, and very reliable. To understand how to test a solid state relay, read on. When you send a signal to it, like pushing a button, it lets electricity pass through. When you stop sending the signal, it stops the electricity. So, it's like having a switch without a physical switch!

Why Test an SSR?

Testing an SSR is important for a few reasons:

  1. Quality Check: We want to make sure our SSR is working perfectly before using it in our electronics work.
  2. Safety: If an SSR isn't working right, it could cause accidents. Testing helps us find and replace bad SSRs to keep everyone safe.
  3. Money Saver: If we find a faulty SSR before using it, we save time and money. We won't have to spend extra fixing problems it could cause later.

Safety Precautions

Before we begin testing, let's talk about staying safe:

  1. Turn Off the Power: Always, always, always turn off the power before testing an SSR. This stops any electricity from flowing and keeps you safe.
  2. Know the Dangers: Understand that SSRs often work with high voltages and strong currents. Be cautious when dealing with powerful electronics.

Test Equipment

To test an SSR, you'll need a few tools:

tool and material needed for testing solid state relay
  1. Digital Multimeter: This is like a magic tool that can measure and check electricity.
  2. DC Power Supply (Optional): Sometimes, you'll need a special power source to test the SSR.
  3. Load (Optional): You might need something like a light bulb to see if the SSR is working right.

How To Test a Solid State Relay| Testing Procedure

You should know the answer to “how to test a solid state relay?” Testing a Solid State Relay (SSR) is an important process to ensure that it's functioning correctly and safely in your electronic circuits. This testing procedure will guide you through the steps needed to assess an SSR's performance thoroughly.

Method 1: Visual Inspection

Before delving into electrical tests, it's essential to visually inspect the SSR for any physical damage or irregularities. Here's what you need to do:

how to check solid state relay
  • Examine the SSR Closely: Carefully inspect the SSR's exterior for signs of physical damage, such as cracks, burns, or any visibly loose connections.
  • Check for Dust or Contaminants: Ensure that there is no dust or foreign contaminants that may hinder the SSR's performance.

If you discover any issues during this visual inspection, it is highly advisable not to proceed with testing. A damaged SSR should be replaced to ensure the safety and reliability of your electronic circuit.

Method 2: How To Test a Solid State Relay with multimeter?

The continuity test checks if the SSR's internal "gate" can be opened and closed correctly. Follow these steps:

how to check solid state relay with multimeter
  • Set the Multimeter: Turn your digital multimeter's dial to the continuity mode. This mode usually has a symbol that resembles a sound wave.
how to set mutlimeter on continuity mode
  • Probe Connections: Connect the multimeter probes to the control terminals of the SSR. These terminals are typically labeled "Input" or "Control."Connect the black (common) lead of your multimeter to one of the control terminals .Connect the red (positive) lead of your multimeter to one of the input terminals.
how to set connnect multimeter probes to solid state relay
  • Listen for a Beep: If the SSR is in good working condition, the multimeter should emit a beep. This indicates that there is electrical continuity between the control terminals. In simpler terms, it confirms that the SSR can open and close its internal "gate" when the proper signal is applied.

The continuity test is crucial as it verifies the basic functionality of the SSR's control mechanism. If the SSR fails this test (i.e., there is no beep), it is likely defective and should not be used in your circuit.

Method 3: Diode Test

The diode test examines the SSR's internal diode, which plays a vital role in its operation. Here's how to perform this test:

  • Set the Multimeter to Diode Mode: Adjust your multimeter to the diode mode setting, often represented by a diode symbol.
how to set multimeter on diode mode
  • Probe Connections: Connect the multimeter's positive probe to the load terminal of the SSR and the negative probe to the common terminal.
  • Check the Voltage Drop: In a healthy SSR, the multimeter should display a forward voltage drop of approximately 0.7 volts. This indicates that the diode inside the SSR is functioning correctly, allowing current to flow in the intended direction.
  • Reverse the Probes: Swap the positions of the multimeter probes. When you do this, the multimeter should display "OL" (Open Line) or "1," signifying an open circuit. This confirms that the diode prevents current from flowing in the wrong direction.

The diode test is essential because the diode ensures that electricity flows in the right direction through the SSR. A faulty diode can lead to unpredictable behavior in your circuit, making this test critical for SSR functionality.

Signs of A Faulty Solid State Relay

Understanding the signs of a faulty solid state relay is crucial for preventing unexpected equipment failures and ensuring safety. In this guide, we will explore the common symptoms of a failing SSR.

1. Overheating

Signs of A Faulty Solid State Relay

One of the most noticeable signs of a faulty SSR is overheating. When an SSR is in operation, it generates heat, but excessive heat can indicate a problem. Overheating can occur due to various reasons, including overloading, poor heat dissipation, or component failure within the SSR itself. If you notice the SSR becoming abnormally hot, it's a clear indication that something is wrong.


  • The SSR casing is too hot to touch.
  • Burn marks or discoloration on the SSR.
  • Surrounding components or wiring insulation shows signs of heat damage.

2. Intermittent Operation

Intermittent operation is another common sign of SSR failure. An SSR should reliably switch a load on and off when commanded. If it starts behaving erratically, turning the load on and off unpredictably, it can lead to equipment malfunctions or dangerous situations in industrial settings.


  • Inconsistent operation where the load is not reliably turned on or off.
  • Occasional failure to respond to control signals.
  • Intermittent loss of power to the load.

3. Increased On-State Voltage Drop

A healthy SSR should have a relatively low voltage drop when in the on-state, which means it allows current to flow through with minimal resistance. However, as an SSR ages or begins to fail, the on-state voltage drop can increase. This can result in higher power losses and decreased efficiency in your circuit.


  • A noticeable increase in voltage drops across the SSR when it's in the on-state.
  • Reduced voltage at the load compared to the input voltage.

4. Excessive Leakage Current

Leakage current is the small amount of current that flows through an SSR even when it's supposed to be in the off-state. An SSR with excessive leakage current can cause unintended activation of connected devices and lead to overheating or damage.


  • Connected devices or loads turning on or flickering when the SSR should be off.
  • Measured leakage current exceeding the SSR's specifications.

5. Failure to Turn Off

One of the most critical functions of an SSR is to turn off the connected load when commanded. If the SSR fails to do so and the load remains energized, it can lead to equipment damage, electrical hazards, or even fires in extreme cases.


  • The connected load remains on even when the control signal to the SSR is off.
  • Continual current flows through the SSR when it should be off.

6. Failure to Turn On

Conversely, an SSR that fails to turn on when commanded can also be a sign of a malfunction. When the control signal is applied, the SSR should promptly allow current to flow through to the connected load. Failure to do so can disrupt operations and cause delays.


  • The connected load remains off even when the control signal to the SSR is on.
  • No current flows through the SSR when it should be on.

7. Audible Noise or Clicking

Healthy SSRs operate silently. However, a failing SSR may produce audible noise, such as clicking or buzzing sounds. This noise can indicate that internal components are deteriorating or making poor contact.


  • Audible clicking, buzzing, or humming sounds when the SSR is in operation.
  • Changes in the noise pattern when the SSR is subjected to different loads or conditions.

8. Visual Damage

Physical inspection can reveal signs of SSR failure. Examine the SSR for any visible damage, including burn marks, discoloration, or loose connections. Physical damage is often an outward sign of internal problems.


  • Burn marks or scorching on the SSR casing or circuit board.
  • Loose or disconnected wires or terminals.


If the SSR fails any of these tests, it's likely broken and should be replaced. Don't use a broken SSR in your electronics because it could cause problems, be unsafe, and even damage other parts.


Testing a Solid State Relay is not as hard as it might seem. It's like giving it a little checkup before it goes to work in your electronics. By following these steps, you can make sure it's healthy and ready to do its job. Remember to stay safe, and if you find a bad SSR, don't hesitate to replace it. That way, your electronics will work smoothly and stay safe too! We hope now you know “how to test a solid state relay?”