Which Three Criteria Do You Choose When Selecting a Relay?

In my past experience of selecting relays, I always found it challenging to consider all the factors involved. However, after careful analysis, I've narrowed it down to three key criteria that should guide your decision-making process.

1) The primary technical performance of the relay, such as contact load capacity, operating time, mechanical and electrical lifespan, must meet the system's requirements. These parameters are crucial for ensuring reliable and long-term operation.

2) The structural design and physical dimensions of the relay should be suitable for the intended application environment. This includes considerations like mounting method, space constraints, and environmental conditions.

3) Cost-effectiveness is another important factor. While high-performance components are essential, they should also be economically viable and provide good value for money without compromising on quality.

What Causes Unstable Relay Operation?

Based on my own experience, unstable relay operation can typically be attributed to three main causes.

1) Unstable power supply: This can occur due to several reasons, such as excessive voltage ripple, insufficient voltage levels, or variations in coil resistance. These issues can lead to erratic behavior and failure to operate correctly.

2) Instability in relay parameters: This may result from physical damage, such as drops or strong impacts, or internal faults like short circuits between the coil windings. These problems can cause inconsistent switching and reduced reliability.

3) Relay malfunction: This often occurs due to improper programming logic or exposure to harsh environmental conditions. It’s important to ensure proper control and protection mechanisms are in place to avoid such issues.

Why Is the Relay Not Releasing?

From my understanding, there are usually two main reasons why a relay might fail to release. One is related to the coil itself, and the other is due to a fault in the circuit.

If the residual voltage at the coil terminal is too high, the relay will not release. This could happen for several reasons: 1) Energy storage components on the other end of the coil, such as capacitors, may retain charge; 2) There may be leakage current or bypass current through the coil; 3) The remaining voltage in a semiconductor circuit might be too high.

Additionally, faults in the control circuit can also prevent the relay from releasing. For example, if the circuit experiences a drop in voltage, suffers from physical impact, or has issues with contact integrity, the relay may not respond as expected.