How to Test and Diagnose Faulty Relays > 자유게시판

Testing and diagnosing faulty relays is an essential skill for anyone working with electrical systems, whether in home applications. Relays are simple devices that use a small electrical signal to control a high-power circuit, and when they fail, they can cause everything from a car that won’t start.

The good news is that most relay problems can be identified with common household equipment and a methodical approach.

Start by understanding the relay’s role in the circuit. Relays typically have five terminals labeled 30, 85, 86, 87, and 87a. Terminal 30 is the primary connection, 85 and 86 are the coil terminals that receive the trigger voltage, and 87 and 87a are the switched paths. When the coil is energized, the relay switches from 87a to 87, completing or breaking the circuit.

The first step in diagnosis is a physical examination. Look for signs of charring, deformation, or rust on the plastic casing or terminals. If you see any damage, the relay is defective and should be installed with a new unit. Also check the holder the relay plugs into. bent, or corroded pins can mimic a bad relay.

Next, use a multimeter to test the relay’s coil. Set your multimeter to measure resistance. Place the probes on terminals control terminals. A good winding should show a resistance between 40–150 ohms, depending on the relay type. If the reading is infinite or less than 10 ohms, the coil is shorted and the relay is no longer functional.

Now check the contacts. With the relay removed from the circuit, place the multimeter probes on terminals 30 and 87a. You should get a reading of open circuit because, رله in the de-energized condition, these contacts are open. Then place the probes on 30 and 87. You should also get infinity, as 87 is off by default. If you get a closed circuit here, the relay contacts are stuck closed, which is a major fault.

To test the switching function, you need to trigger the electromagnet. You can do this by connecting a 12V DC power supply to terminals 85 and 86. You should hear a clear mechanical sound as the relay activates. If you hear no sound, the coil is non-functional. If you do hear a click, immediately check continuity again between the output contacts. You should now get a low resistance reading, indicating the contacts have closed. If there’s still an open circuit, the armature are damaged.

Another quick method is the swap test. If you have a identical replacement of the same type, substitute it and see if the system works. If it does, the original relay was bad. This is especially useful in equipment where relays are commonly interchangeable.

Always remember to turn off the ignition before removing or replacing a relay. And when in doubt, consult the vehicle or equipment manual for the appropriate amperage rating. Some relays are designed for specific current loads, and using the unsuitable substitute can cause system failure.

Most relay failures are caused by long-term use, poor ventilation, or power fluctuations. Regular inspection and replacing relays at the first sign of intermittent behavior can prevent bigger problems. Keep a standard automotive relays on hand as backup units, especially if you work with systems that depend on them constantly.

Testing relays isn’t complicated, but it requires careful procedure. By combining physical check, electrical measurements, and a basic understanding of how relays work, you can accurately identify and replace most relay-related issues.