The are some items to quantify fan life:

  • MTTF- Mean Time to Failure
  • MTBF- Mean Time between Failure
  • L10- Failed to 10% Times

Testing a batch of fan, untill some of them fail, and then caculate the fan life time. The failure criteria include:

  • Fan not function.
  • Current over 15% of original.
  • Speed under 15% of original.
  • Noise over 3dB(A) of original.

MTTF Test Procedure and Calculation Method

  1. Random sampling 50 units.
  2. Perform function test in advance and set up temperature.
  3. Function test once a week.
  4. Test time for at least 3000 hrs.
  5. Based on Total Test Hours( T ) and Failure Quantity ( r ) and refer Chi-Square table with Confidential Level (CL) to get MTTF.


t : Total test time

χ : Chi- Square table

α : Producer ’s risk ; α=10% (CL:90%;CL=1- α )

: Failure Q ’ty

υ: Degrees of freedom, υ=2γ+2;





MTTF 28020
test sample 50
Test Time 3000
Fail quantity 2
Failure first time 2400
Failure second time 2736
Total test hour 149136
coefficient 10.645