Calculating Mean Time Before Failure (MTBF) for a solid-state relay is, at best, a tricky proposition. Unlike a typical electromechanical relay, there are several variables that will directly impact the life expectancy of a solid-state relay in a given application. These variables primarily revolve around the electrical characteristics of the application, such as load current, the duty-cycle of the load, the ambient temperature inside the panel, surge currents, etc. However, mechanical issues such as the mounting method, available airflow, and thermal interface between the relay and the panel / heat sink also impact the relay’s life expectancy.

Therefore, Crydom does not publish a “fixed” MTBF specification. Instead, we provide an estimated MTBF specification range based on historical observation. That is, we calculate the MTBF by taking the total in-service hours over the previous two-year period and dividing that by the number of returns we have received from the field over the same period of time (solid-state relays that were misapplied by the customer are not considered in the calculation). “In-service hours” is simply calculated by taking the number of products shipped over the specified period and assuming that they were in operation for eight hours per day over a five day work week. Then, to ensure that we maintain an adequate margin of error, we assume that only 10% of all field failures are returned to us for analysis and adjust the results accordingly.

The final result yields a MTBF rating of between 2 million and 40 million hours, depending upon the product family. However, for the sake of simplicity we state that the MTBF rating for our solid-state relays is >2 million hours with a quality level of approximately 10PP