ambient temp is 69.3, so not sure why you wouldn't use that
but also if you want to be conservative, use 110
but the important part is what the definition is in your your equation/reference.
HI Jared ,
Thank you for the reply.
I am calculating the life of electrolytic capacitor, using the Arrhenius' Law of Chemical Activity.
the formual is as follows,
L2= L1 ( Vr/Vo) * 2^( (Tm-( Ta- dT)/10))
Ta= Ambient temprature
Tm= Maximum temp rating of capacitor
dT= Temprature reise from ripple current
Vr= Maximum Voltage rating of capaciotr
Vo= operating Voltage of application
L1= load life rating
L2 = Projected life of operating conditions
My operating range of equipement is 10 to 40 degere centigrade.
While we performed the Thermal analysis using the solid works we have follwing results for tempratue
Thermal analysis was performed for ambient temprature ( considering worst case )40 degree
=> Internal temprature ( enclouser) was 69.3 deg'
=> The approx temprature on the PCB was 110 deg
So for calcuating life of the capacitor which temp. should we considered?
so if we taking the capacitor having load life rating of 2000 hr , and teh ambient of 63.2 degree then the maximum life will be 5 yeras .
if we considerred teh 110 degree then predicted life will be approx 2 yerars.
We have requiremtn for 6 years of life for teh equipment .
What should be the correct temprature ( ambient) should be cosidered?
I think dt is more important.
What vale will you use there?
Failure of components:
It is best to go to the component manufacture for MTBF calculation process. Using only temperature as the metric for MTBF was used in the 1950s. Components will fail due to stress, vibration, thermal cycling... etc not just chemical reaction form a constant elevated temperature.
You state that the temperature range is 10 to 40°C but what percent of the time will the ambient be at 40°C?
If your PCB is at 110°C I think that you have other problems with other components. You need a better thermal path from the PCB to the ambient air.
Ta is the temperature of the air close to the component
Tm is the temperature of the case or material