When developing a new electric product, the designer does not have enough information while selecting the proper fan. The spec sheet is not clear on the lifespan of the part. Typically, an engineer can expect a lifespan from 50,000 to 70,000 hours, running in predetermined conditions. Real life will be shorter if the unit is under stressed environmental cycles.
Fan Life Expectancy
Most fan failures occur due to the motor insulation or ball bearings, where the bearing life is affected by temperature and speed. Bearing failures occur frequently compared to fan motor insulation breakdowns.
L10 as a probability factor
The Lx factor, featured in many fan data sheets, indicates the percentage of devices that failed after the period defined by the number of operational units.
The L10, in the case of fans, is a statistical figure determined by observing a larger quantity of operating units where 10% of running fans fail and 90% of the same population will survive.
The same for bearings is called the B10 probability factor, where 10% of the units under test fail, and 90% of the same population will survive.
The MTBF as life expectancy
Several fan manufacturers will rank their product as 200,000 hours long by referring to the MTBF figure rather than the L10 factor.
The MTBF is an exponential failure rate where 63.2% of a given group of components have failed.
In the case of fans, the L50 factor corresponds to half of the population that will fail.
The difference between the two estimate methods is the calculated failure rate. The L10 factor is the most commonly used prediction to determine the fan life expectancy.
Consider a fan a non-repairable part, which is why the MTTF estimate applies.
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