Common faults and maintenance methods for low-voltage electrical appliances - Solutions - Huaqiang Electronic Network

Low-voltage electrical appliances are widely used in various electrical circuits, and each has a unique structure. To effectively maintain and troubleshoot these devices, it's essential to first understand the common faults and repair methods of their basic components before moving on to specific types of low-voltage equipment.

1. Common Faults and Repairs of Low-Voltage Components

1.1 Contact Failure and Maintenance

(1) Overheating Contacts: When a contact is closed, current flows through it. Under normal conditions, the contact should not overheat. However, if the contact resistance between the moving and stationary contacts is too high or the current exceeds the rated value, overheating can occur. This may lead to degradation of contact properties or even welding. Causes include excessive current due to incorrect selection of contact capacity, overloaded power equipment, or improper voltage levels. To prevent this, ensure that the contact is properly maintained and cleaned. For example, use a scraper or fine sandpaper to remove oxidation or debris from the contact surface. Avoid using abrasive materials that could damage the contact surface.

Testing contact pressure can be done by inserting a thin strip of paper (0.01 mm thick) between the contacts. If the paper is pulled out easily, the pressure is insufficient. If it tears, the pressure is too high. Adjusting the spring pressure or replacing damaged springs can help restore proper contact force.

(2) Contact Wear: Contact wear occurs due to two main factors: electrical wear from arcs and mechanical wear from impacts during closing. Over time, the contact becomes thinner. When the thickness is about half the original, the contact should be replaced. If wear is excessive, check for issues like improper current rating or frequent operations.

(3) Contact Welding: This happens when the contact surfaces melt and fuse together, preventing the contacts from opening. It often results from high currents, improper contact size, or faulty springs. In such cases, only new contacts can be used. If the problem is due to inadequate capacity, consider upgrading to a higher-rated device.

1.2 Electromagnetic System Failure and Maintenance

(1) Noisy Iron Core: A slight "click" sound is normal, but loud or abnormal noises indicate a fault. Issues may include poor contact between the armature and iron core, dirt on the surface, or a damaged short-circuit ring. Cleaning the surfaces or replacing the short-circuit ring can resolve this.

(2) Coil Failure: Coil overheating or burning can result from incorrect voltage, mechanical damage, or inter-turn short circuits. If the coil is burned out, it should be rewound. Minor short circuits can sometimes be repaired by removing the affected turns.

(3) Arc Extinguishing System Failure: Damage to the arc extinguishing cover, moisture, or carbonization can prevent effective arc extinction. Repair involves drying, cleaning, or replacing damaged parts.

2. Common Low-Voltage Electrical Faults and Maintenance

2.1 Contactor Faults and Maintenance

(1) Phase Loss: Poor contact or loose screws can cause phase loss, leading to reduced motor speed and a loud "click" sound. Immediate maintenance is required.

(2) Contact Welding: High operating frequency, overload, or insufficient spring pressure can cause contact welding. If this happens, the motor will not stop even when the stop button is pressed. Disconnect the power and perform repairs immediately.

(3) Phase-to-Phase Short Circuit: Malfunctioning interlocks or rapid switching can cause short circuits. Use contactor and button interlocks to control motor direction safely.

2.2 Thermal Relay Faults and Maintenance

(1) Blown Thermal Element: Caused by excessive current or short circuits. Replace the thermal relay after fixing the circuit issue.

(2) Malfunctioning Thermal Relay: Too small a setting or long start-up times can cause false trips. Adjust settings or replace wires as needed.

(3) Thermal Relay Not Operating: Could be due to a blown element, incorrect setting, or improper wiring. Check and adjust accordingly. After tripping, allow 2 minutes for cooling before resetting.

2.3 Time Relay Failure

Air leakage or dust in the air chamber can affect delay time. Clean or replace the rubber membrane to restore normal operation. Temperature changes and long-term storage may also impact performance, so adjustments may be necessary.

2.4 Speed Relay Failure

If the motor cannot brake properly, it may be due to misadjustment or broken components. Inspect the rear cover and make necessary repairs.