Hi, My post was to give a bit of background on electrolytic capacitors in respect to specified temperature and lifetime and not a specific reply to you, Chetan. I know that I was confused about the very low lifetime specification before I found out what it exactly meant. Normally you chose a temperature rating for a component based on the ambient temperature for it (and perhaps a power dissipation) but not so for electrolytic capacitors, where you chose a temperature rating based on both expected lifetime and ambient temperature. /Ruben On Fri, 11 Aug 2017 01:33:08 -0700, Chetan Bhargava wrote: > I very well understand that the caps have a lifetime. Mouser has a > parameter on the hrs. I do not know what is the lifetime hrs on the > existing caps. I have chosen the best lifetime on the Panasonic caps > that I ordered. >=20 > I agree with you that the ESR of the caps depend on the temperature > averaged on the lifetime of the cap. >=20 > I have chosen better part given the specifications. Temp rating is > still 105 degrees. Most power supplies have a cap rated for 105 > degrees. Any reason why should I choose a cap rated > 105 degrees? >=20 > Thanks, >=20 > Chetan Bhargava > http://microz.blogspot.com >=20 >=20 > On Fri, Aug 11, 2017 at 1:06 AM, wrote: >> >> Note that an electrolytic capacitor has a temperature rating and a >> lifetime rating in hours. The lifetime is usually rated between 1000 and >> 5000 hours. The lifetime is the time before a certain change in >> percentage in the characteristics of the capacitor. Usually this is a >> change of 30% of the capacitance, the dissipation factor changes to more >> than three times the upper limit or the impedance becomes more than 3 >> times the stated limit. Check for each manufacturer though because the >> lifetime can be specified differently. >> >> The temperature is the temperature internally in the capacitor which >> can be higher than the ambient temperature because of the ripple current >> and the ESR. >> >> The specified lifetime is when the capacitor is operating at its >> specified temperature. The lifetime doubles with every 10 degree >> decrease in temperature. >> >> Therefore it is very important to chose the right part based on the >> expected lifetime for the device (which should be stated in the >> requirement specification) and the maximum expected temperature >> internally in the capacitor. So the temperature rating must usually be >> much higher than the expected ambient temperature, otherwise the device >> can fail much earlier than its expected lifetime. >> >> How much lower the operating voltage is compared to the specified >> maximum operating voltage of the part also has a positive effect on the >> lifetime but this is much lower than the effect of lower temperature. >> >> /Ruben >> >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .