Which Rating is more important for cooling fans MTBF or L10 Service Life

MTBF or L10 Service Life?

We receive a few calls each quarter from our engineer customers asking for the MTBF rating of one of our DC fan models so they can calculate the total MTBF of their system. While this is an important rating, we prioritize the reliability of DC brushless fans measured by the L10 service life rating rather than the MTBF. Here is why:

MTBF (Mean Time Between Failures):

This rating is estimated by performing calculations based on the electronic components (discrete components, ICs, etc.) used in the fan and is in the millions (1.5 to 3 MTBF in hours).

L10 Service Life:

This rating is commonly used in the cooling fan industry and is measured in thousands of hours at a specific ambient temperature.  It is determined by the life span of the grease and bearings used in the fan (see Figure below).

structure of ball bearings in SANYO DENKI cooling fans

Why L10 Life Matters - Measured Temperatures

The L10 life rating is defined as the expected number of hours of continuous fan operation where 90% of fans will meet or exceed. This rating is dependent on the ambient temperature of fan operation. However, note that most of our fan series have 0% failure when reliability tested so are actually higher rated than the L10 rating we publish.

For example, the 9RA series has L10 service life of 60,000hrs at full speed at 60C, which is almost 6.8 years, determined by the grease and bearings life expectancy.

Specification chart with Life Expectancy of cooling fans

But when accelerated life testing was completed on this series, we had a 0% failure rate.

Since the L10 is much shorter than the MTBF this is why we recommend using L10 life as the primary factor for determining expected life because it will be much more accurate than MTBF.

Why L10 Life Matters - Measured Temperatures

The other major factor to consider is the ambient temperature given in the L10 life rating. SANYO DENKI measures our L10 life at a rigorous 60°C specification as it shows the expectation of life at a worst-case operating condition. When operating at lower ambient temperatures, the life will increase as can be seen from the rating of the 9RA series fan at 90,000hrs @ 40°C. Even with this increase in extended life, the L10 life is still the driving factor for life expectancy compared to MTBF life ratings.

In closing, we always recommend using L10 service life as the primary factor for determining expected life because it will be much more accurate than MTBF, as it is a shorter time span and is based off the life expectancy of the grease and bearings. Please contact your local SANYO DENKI sales representatives or sales office if you have any questions.

Written by Gary Masessa


SANYO DENKI has been a trusted provider of cooling solutions for various industries, with fans being a crucial component in many advanced devices. Contact us for a quote, or to discuss your device's customization requirements.

Our experienced application engineers and field engineers will provide support on the customization or any other technical support for your equipment. Contact our representatives or distributors to start discussing your next project.

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