The electromechanical relay has always been the preferred switching mechanism of mains electrical power for many decades. It has been continuously developed and performance improved over time to suit a wide range of applications.
The general expected operation (electrical) lifetime of relays is often rated as 100,000 electrical switching operations in accordance to VDE IEC 61810-1 standard. In many applications the relay can easily reach the 100,000 switching milestone after which reliability can be compromised due to contact degradation.
Transient and arcing occurs during relay ‘make’ (close), ‘break’ (open) and contact bounce. When an arc is present, it can drastically lower the life expectancy of relays. The Engineers’ Relay Handbook (6th edn, 2006), indicate that over 70% of relay failure take place at the contacts. The most prevalent relay failure mechanisms being increased contact resistance, contact contamination and material loss.
Relay contact life expectancy is commonly a function of how much arcing can be withstood before failure occurs. Duration of arc is often determined by the contact’s separation speed. Arcing particularly during switching of inductive loads in high-voltage circuits can be extremely destructive. To achieve maximum contact life, reliable arc suppression is very important. It is difficult to prevent all arcing, but employing arc suppression circuit will extend contact life.
“IES5541A with its contact protection technology will provide better relay reliability and extended relay lifetime. Ideal for temperature control with thermal loads “
Fig 2: Commonly used relay contact protection circuit
The main drawback of commonly used relay contact protection circuit is it introduces long relay release time. To ensure efficient arc suppression and to prevent relay premature failure, selecting the right circuitry and components values is critical. The Engineers’ Relay Handbook (6th edn, 2006) also noted that incorrect use of suppression circuit could result in undesirable effect.
A more complicated suppression circuit is generally needed to reduce RFI at relay.
The IES5541A is the ideal solution as:
- It removes the problem of selecting the right protection circuit and components
- Proven and tested to give efficient arc suppression
- Reduce EMI/ RFI
- Reduce circuit design time
Figure 3 shows unprotected relay contact taken after 100,000 operations (switching 8A resistive load at 230V) showing significant material loss to surrounding areas indicate that the relay is now unable to switch reliably and has reached its expected lifetime.
Figure 4 shows protected relay with IES5541A taken after 100,000 operations (switching 8A resistive load at 230V) showing minimal material transfer indicate that the relay is still able to switch reliably past its expected lifetime.