How to Test a 5-Pin Relay with a Multimeter: Step-by-Step Guide

How to test a five prong relay with a multimeter?

To test a five prong relay with a multimeter, you need to ensure that all the connections are functioning correctly. Start by identifying the terminals of the relay. A typical five prong relay has five distinct terminals labeled as follows: 85 (coil +), 86 (coil -), 87 (common), 87a (normally open), and 30 (normally closed). Understanding these labels is crucial for accurate testing.

First, set your multimeter to the resistance (ohms) mode. This setting will help you check the continuity between the terminals. Disconnect the relay from the circuit to avoid any electrical interference. Place one probe on terminal 85 and the other on terminal 86. You should read a low resistance value, typically around 100 ohms, indicating that the coil is intact. If the reading is infinite or very high, the coil may be faulty.

Next, test the normally open (NO) and normally closed (NC) contacts. Place one probe on terminal 30 and the other on terminal 87. With the relay not energized, you should get an infinite resistance reading, indicating that the NC contact is open. Now, place one probe on terminal 30 and the other on terminal 87a. Again, with the relay not energized, you should read a low resistance, confirming that the NO contact is closed. To further verify, apply power to the relay by connecting a battery across terminals 85 and 86. The relay should click, and the resistance between 30 and 87 should now be low, while the resistance between 30 and 87a should be infinite.

Additionally, you can test the relay's diode protection. Many relays have a diode across the coil to protect against voltage spikes. Set your multimeter to the diode test mode. Place one probe on terminal 85 and the other on terminal 86. You should see a forward voltage drop, usually around 0.6 to 0.7 volts, indicating that the diode is working. Reverse the probes and the reading should show infinite resistance, confirming the diode’s functionality. If the diode test fails, it could indicate a potential issue with the relay’s internal components.

How much resistance should a 5 pin relay have?

Typical Resistance Ranges for 5 Pin Relays

A 5 pin relay’s coil resistance typically ranges between 60–200 ohms for a standard 12V automotive relay, though this varies based on design and application. Lower-voltage relays (e.g., 6V) may have higher resistance (e.g., 200–400 ohms) to limit current, while higher-voltage models (e.g., 24V) often fall between 120–470 ohms. The exact value depends on the relay’s coil specifications, with lower resistance indicating higher current draw. Always check the manufacturer’s datasheet for precise values, as resistance is not standardized across all 5 pin relays.

Factors Influencing Coil Resistance

Coil resistance in a 5 pin relay is determined by three key factors:

• Voltage rating: Higher voltage relays require thicker or longer coil windings to reduce current, increasing resistance.
• Power consumption: The coil’s power (in watts) is calculated as Voltage² / Resistance; lower resistance draws more current but provides stronger activation force.
• Type of relay: SPST (single pole, single throw) and DPDT (double pole, double throw) relays may have slightly different resistance ranges based on their contact configurations.

Environmental factors like temperature can also cause minor fluctuations in measured resistance.

Testing and Troubleshooting Resistance

To verify a 5 pin relay’s coil resistance:

1. Disconnect power and use a multimeter set to ohms mode.
2. Test between the two coil terminals (typically pins 85 and 86). A reading of 0 ohms or ∞ ohms indicates a shorted or open coil, respectively.
3. Compare the result to the datasheet. Significant deviations may signal a faulty relay.

Note that resistance alone doesn’t guarantee relay functionality; mechanical wear or contact issues may exist even with normal resistance readings.

How do you tell if a relay is bad with a multimeter?

Testing the Relay Coil Resistance

To determine if a relay is faulty, start by testing the coil resistance with a multimeter. First, disconnect the relay from power and locate the coil terminals (usually labeled "+", "-", or "85/86" for 12V relays). Set the multimeter to the ohms (Ω) setting and touch the probes to the coil terminals. A healthy relay coil typically has a resistance between 60–200 ohms, depending on voltage (e.g., 12V or 24V systems). If the meter reads OL (open circuit) or a drastically low/high resistance, the coil is likely damaged, indicating a bad relay.

Checking Contact Continuity

Next, test the relay’s contact continuity. Set the multimeter to the continuity or low resistance mode. For the normally open (NO) contact, place one probe on the common (COM) terminal and the other on the NO terminal. There should be no continuity when the relay is unpowered. Then, energize the coil by connecting a 12V battery or power source to the coil terminals. While applying power, retest continuity between COM and NO—the meter should beep or show 0–30 ohms if the contacts are functioning. Failure to switch properly means the contacts are stuck or corroded.

Measuring Voltage Drop Across the Coil

A voltage drop test can reveal hidden issues. Connect the multimeter in series with the relay’s power supply to measure voltage drop while the relay is active. For example, place the meter probes between the battery positive and the relay’s power terminal, then between the coil’s ground terminal and the battery negative. If the relay is working, the voltage drop across the coil should be minimal (under 0.5V). A higher voltage drop indicates internal resistance, suggesting the coil is failing even if it partially works. This test helps identify relays that are degraded but not fully dead.

Testing these components systematically ensures accurate diagnosis, avoiding unnecessary replacements. Always ensure the relay is disconnected from the circuit during resistance tests and use proper safety precautions when applying power.

How to check 5V relay with multimeter?

Step 1: Check Continuity in the Relay Coil

To verify the relay’s coil functionality, set your multimeter to continuity mode (or resistance mode). Disconnect the relay from power and touch the probes to the coil terminals. A working coil should show low resistance (typically 60–200 ohms for 5V relays) and trigger a continuity beep. If there’s no beep or resistance is extremely high, the coil is likely faulty or broken, indicating the relay needs replacement.

Step 2: Test the Relay Contacts (NO/NC)

Check the normally open (NO) and normally closed (NC) contacts when the relay is de-energized. Set the multimeter to continuity mode again. Touch one probe to the common (COM) terminal and the other to the NC terminal. A valid connection (beep) confirms the NC contact is closed. For the NO contact, apply 5V to the coil temporarily (using a battery or power supply), then test between COM and NO—continuity should now exist here while the coil is energized.

Step 3: Measure Voltage Across the Coil

Power the relay’s coil with a 5V source and set the multimeter to voltage mode. Place the probes on the coil terminals to ensure the applied voltage matches the rated 5V. If voltage drops significantly (e.g., below 4.5V), the coil may be overloaded or resistive, affecting the relay’s switching performance. Additionally, test for voltage at the control signal input to confirm the circuit is delivering adequate power to activate the relay.

Ensure all tests are conducted safely, with the relay disconnected from the main circuit when not powered. Irregular readings in any step suggest a malfunction requiring component replacement.