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Also, another parameter used in the attached lifetime equation is called “alpha”. It is the “ratio of the case top and core of the capacitor element”. From the attached lifetime exerpt, you can see that the lower the diameter of the capacitor body, the greater the temperature of the capacitor case gets. Is this typical for other electrolytic capacitors too?...it doesn’t seem to make sense…..because surely the deciding factor is how long the capacitor body is?....that is, longer body capacitors would run hotter as its further from the internals to the base…the base being where most heat transfers out of the capacitor...
Where did you get the ESR number? It obviously contradicts the ripple current specification as the calculated > 70K temperature rise with rated current reveals. Either one or the other specification is wrong.The equation 4.7 seems to give better numbers when a really low ESR is used. (say less than 0.1 ohms). However, the ESR of the 100uF, 450V capacitor is 3.32 ohms at 120Hz…..this high value of ESR gives nonsense values for lifetime.
It is from (Dissipation Factor * Xc) = 0.25 * 1/(2.pi.120.100u)Where did you get the ESR number?
The application note instructs you not to use the equation for ΔTj>20K.Also, if either of the temperature rise expressions becomes equal to 40 degC, then the lifetime equation fails because of “divide by zero”.
Can you confirm that the load life quoted at the top of an electrolytic capacitor datasheet, is simply the life with zero ripple current in it, at the maximum ambient temperature?
You are reading the equations wrong. Lb and ΔTj0 are both determined by the capacitor design. ΔTj0 is e.g. 5K for the capacitor series under discussion.According to this equation, as delta_Tj0 increases, so too does lifetime.
That doesn’t make sense…..if the internals were getting hotter, then lifetime should get less.
You are reading the equations wrong. Lb and ΔTj0 are both determined by the capacitor design. ΔTj0 is e.g. 5K for the capacitor series under discussion.
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