10°C doubling rule for life

Capacitor manufacturers recommend that in general we don t pass any more current than the maximum rated ripple current. This ripple current is the one specified at the worst case ambient (e.g., 105°C). Even at lower temperatures we should not exceed this current rating. No temperature multipliers should be used. Because only then is the case to core temperature differential within the design specifications of the part. And only then are we allowed to apply the simple 10°C doubling rule for life. 

When the differential is decidedly kept equal to or less than the designed-in value, the life of the elko is then determined by the familiar doubling rule — for every 10°C fall in core temperature (from its maximum rated), the life doubles. That is how we can finally get the required 44 khours. For example if the core is correctly estimated to be at 65°C, then the calculated life of a 2000 hour capacitor is actually 2000 x2x2x2x2x2 = 64 khours. 

In this respect 6,2 is called antioxidant depletion time and E the apparent activation energy of antioxidant depletion. Again values for E in the vicinity of 50kJ/mol are experimentally found. As discussed in Sect. 5.1, the Arrhenius equation leads to the old mle of thumb that an increase in temperature by about 10 °C doubles or trebles the depletion rate. This rule can also be used as an initial guide to estimate service life. If, after ageing of geomembrane samples in water or air at 80 °C test temperature over a period of at least one year, effective stabiliser substance can still be found, for example by OIT-measurements, a service lifetime of many decades can be expected at normal ambient temperatures. 

Although temperature is the most common method of ageing materials, it is inappropriate when the issue is the radioactive degradation of any material. However, in practice temperature is a key parameter affecting chemical kinetics, and its use is normally based on the application of Arrhenius kinetics. In the absence of mechanistic information, the normal practice is to use the rule of thumb (the rate of reaction doubles per 10 °C rise) to identify a simulated age. However in practice, this is rarely true for many materials and multi-material assemblies and questions the validity of accelerated ageing trials based upon this rule of thumb. Therefore great caution is required in the use of Arrhenius kinetics in life prediction [2]. 

Elevated temperature is often used to estimate the in-can stability of adhesives and sealant formulations. This is usually applied by a simple rule of thumb that says the reaction rate of the degradation mechanisms involved doubles for every 10°C increase in temperature, and therefore 1 week storage at 50°C approximates to 8 weeks at room temperature (20°C). Application of this rule will likely be conservative in the prediction of shelf life and must be verified by real-time validation testing conducted at room temperature for the targeted shelf life. 

---