What are common relay faults and how to detect and handle them?

A relay is one of the most commonly used actuating elements in electronic equipment. It is an electronic control device that consists of a control system (also called the input circuit) and a controlled system (also called the output circuit). It is typically used in automatic control circuits, and is also used in communication equipment such as PCM devices. In essence, it is an "automatic switch" that uses a smaller current to control a larger current. Therefore, it plays roles such as automatic regulation, safety protection, and circuit switching in circuits. The following mainly analyzes several common relay faults and their handling methods:

1. Loose or cracked contacts
The contact is the electrical contact component that completes load switching in a relay. Some products have contacts assembled by riveting or press-fitting, and the main defects are loose contacts, cracked contacts, or excessive dimensional or positional deviation. This will affect the contact reliability of the relay. Loose contacts are caused by unreasonable dimensions in the matching area between the spring leaf and the contact, or improper adjustment of the riveting pressure by the operator. Cracked contacts are caused by excessive material hardness or excessive pressure. For contacts made of different materials, different material processing techniques should be adopted. Some contact materials with higher hardness should be annealed before contact manufacturing, riveting, or spot welding. Contact manufacturing should be done carefully, as material tolerances exist; therefore, the cutting length should be determined by trial before each batch. Contact manufacturing should not produce burrs, indentation damage, or incomplete filling. Off-center contact riveting is caused by the operator not aligning the die correctly or by misalignment between the upper and lower dies. Contact damage and contamination are caused by oil contamination and metal chips not cleaned from the die. Regardless of the defect type, it will affect the operational reliability of the relay. Therefore, during contact manufacturing, riveting, or welding processes, the self-inspection rules of first-article inspection, in-process sampling, and final inspection must be followed to improve assembly quality.

2. Unstable relay parameters
A considerable portion of electromagnetic relay components are assembled by riveting. The main problem is loose riveting or poor bonding strength. This defect can cause unstable relay parameters, significant parameter changes under high and low temperatures, and poor resistance to mechanical vibration and shock. The main causes of this defect are out-of-tolerance riveted parts, improper part placement, substandard tooling and dies, or incorrect installation. Therefore, before riveting and welding, the tooling, dies, and parts to be riveted should be carefully inspected to ensure they meet the requirements.

3. Deformation of riveted electromagnetic system components
Bending, twisting, or upsetting of parts after riveting creates difficulties for assembly or adjustment in subsequent processes, and may even result in scrapping. The main causes of this defect are parts being too long or too short, uneven force applied during riveting, die assembly deviation or design dimensional errors, and improper part placement. During riveting, the operator should first check whether the part dimensions, appearance, and dies are correct. If the die is not properly seated, it will affect the assembly quality of the electromagnetic system or cause core deformation and upsetting.

4. Glass insulator damage
Glass insulators are made by sintering metal pins with glass. During inspection, assembly, adjustment, transportation, and cleaning, pin bending, glass insulator chipping, and cracking can easily occur, causing air leakage and degradation of insulation and withstand voltage performance. Pin rotation can also cause displacement of the contact spring leaf, affecting reliable on/off operation of the product. This requires assembly operators to handle the products with care throughout the entire relay production process. Parts should be neatly arranged in transfer boxes. During assembly or adjustment, bending or twisting of the lead pins is not permitted.

5. Coil faults
Relay coils come in many types, some with outer wrapping and some without. Coils should be stored individually and separately in dedicated containers. If they collide and become entangled, separating them may cause wire breakage. During riveting of the electromagnetic system, the pressure of the hand-operated press and the press machine should be adjusted appropriately. Excessive pressure can cause coil wire breakage, coil frame cracking, deformation, or winding breakdown. Insufficient pressure can cause loose winding and increased magnetic loss. Multi-winding coils generally use different colored leads to identify the start ends. During soldering, care should be taken to distinguish them; otherwise, the coil may be soldered incorrectly. Coils with start-end requirements are generally marked with labels to indicate the start and end terminals. Attention should be paid during assembly and soldering; otherwise, the relay polarity may be reversed.