First, let's look at how SANYO DENKI defines the service life of fans. In the catalog, the expected life of fans is described as follows.
Both the "90% survival rate" and "L10 life" refer to the time it takes for 10% of a population of fans to experience failure. In other words, both define the expected life with 90% reliability.
In general, the service life of a fan is defined as the time at which the following criteria are met: "a certain level of decrease in airflow performance" and "a certain level of increase in noise" after the fan is continuously operated.
SANYO DENKI regards "a certain level of decrease in airflow performance" as "a decrease in the rotational speed of the fan," and defines fan service life as when the rotational speed falls below 70% of the initial rated speed.
The more components are used in an electronic device, the more factors affect its service life. When designing a device, its service life is sometimes defined as being equal to the service life of its electronic components using MTBF (Mean Time between Failures).
Fan service life, however, generally does not depend on the service life of its electronic components, but rather on that of the bearing part of the motor that rotates the blade; i.e., what matters most is the service life of the fan's mechanical parts. There are various types of bearings, but all SANYO DENKI fans use ball bearings for high reliability.
There are two types of ball bearing life: fatigue life and grease life. Unlike industrial motors, the load on the bearings of fans is relatively small, so fatigue life is rarely a problem. Therefore, the grease life of ball bearings is the most decisive factor for the service life of fans.
As stated earlier, the service life of fans is determined by the grease life. Therefore, extending the grease life also extends the service life of fans. The following are the four ways to extend this grease life.
1. Reduce the bearing temperature
2. Reduce the bearing load
3. Use better grease
4. Improve the bearing load capacity
As items 2 to 4 are determined at the time of fan development, it is difficult for users to make further improvements. For item 1 "Reduce the bearing temperature," however, the same effect can be obtained by reducing the ambient temperature of the fan. For example, if a fan* has an expected life of 40,000 hours in a 60°C environment, the expected life increases to 70,000 hours in a 40°C environment.
* Model no.: 9GA0312P3K001
Although fans are mainly used for cooling, by understanding that fans themselves are also affected by the ambient temperature, you can take the ambient temperature into account when selecting fans, contributing to making your device more maintenance-free.
In this session, we learned about the service life of fans. In addition to the expected life, when selecting fans, don't you often compare the maximum airflow values or the maximum static pressure values? In fact, when installed in a device, fans can never deliver either of these values.
In the next session, we'll introduce "airflow vs. static pressure characteristics" of fans.
Date of publication: January 26, 2018