What are the methods for testing a relay?
3 Answers
The methods for testing a relay are: 1. Check contact resistance; 2. Measure coil resistance; 3. Test pull-in voltage and pull-in current; 4. Measure release voltage and release current. The functions of a relay are: 1. Control high-power circuits; 2. Form program control circuits to achieve automated operation. The working principle of a relay is that when a certain voltage is applied to both ends of the coil, the coil generates current, thereby producing an electromagnetic effect. The armature will overcome the pulling force of the return spring under electromagnetic force and move toward the iron core, driving the moving contact of the armature to connect with the stationary contact. Types of relays: 1. Electromagnetic relay; 2. Solid-state relay; 3. Temperature relay; 4. Reed relay; 5. Time relay; 6. High-frequency relay; 7. Instrument-type relay.
When I'm working on car electrical circuits in the garage, I often encounter relay failures. To test it, it's best to first turn off the engine and disconnect the negative battery terminal for safety, then use a multimeter to measure the relay's resistance value. Relays typically have several pins, including coil terminals and contact terminals: the coil terminal resistance should be between 20 to 100 ohms - values too high or too low indicate a burnt coil; the contact terminals should open and close properly, which can be checked by manually activating the coil or using the multimeter's continuity mode to verify if contacts connect when powered and disconnect when unpowered. Don't forget to inspect the relay housing for cracks or burn marks, which often result from prolonged overload or short circuits. If tests show everything is normal but it still doesn't work, the issue might be with external circuits like wire aging or terminal oxidation - I clean contacts and resolder loose wire ends to avoid misdiagnosis. Throughout the process, don't rush to replace parts; systematic troubleshooting saves money and ensures accuracy.
For ordinary people who often DIY car repairs, testing relays should start with the basics: First, locate the corresponding relay in the fuse box, unscrew it, and shake it to listen for a clicking sound—a good relay will respond to power changes. If there's no sound, use a multimeter set to the resistance mode to measure the coil pins: normal readings should be within a few dozen ohms; if it shows infinity or close to zero, the coil is either broken or internally shorted. Additionally, test the contact terminals for continuity, checking if the relay can properly switch circuits under simulated starting conditions. Always ensure a dry environment during testing to prevent electric shocks, as I've found many faults stem from moisture corroding the contacts. Lastly, don't ignore the temperature of the relay's mounting location—if it's overheated, let it cool before testing to avoid burns. Though simple, this method can quickly identify potential hazards.
