CDE Makes It Easy to Handle System Reliability with Aluminum Electrolytic Capacitors

Liberty, SC (November 2005) — Electronic designers are required to calculate system reliability, and they do it by adding the calculated failure rates of all of the components. Until now there was no straightforward or easy way to get failure rates for aluminum electrolytic capacitors. That is a design hindrance that encourages designers to use ceramic and tantalum capacitors instead of aluminum.

Now CDE makes it easy to calculate failure rates for aluminum electrolytic capacitors. This sets CDE apart from other aluminum capacitor makers. All of the life/temperature calculators on our website now furnish failure rate information as well as expected life before wear out. As an introduction to this breakthrough consider first what reliability engineers call the bathtub reliability curve.

The accepted model for reliability of electronic components is the classic bathtub reliability curve shown below. It's a curve plotting failure rate of any population of electronic components versus time, and it looks like a bathtub. In the early life of components - the left end of the tub - failure rate decreases rapidly as the infant mortals, the ones that have manufacturing defects, fail early and die off. Then during normal life - the bottom of the tub - the failure rate settles to a low, constant level. And at the end of life - the right end of the tub - failure rate increases rapidly as components wear out.

Until now CDE and other aluminum electrolytic capacitor makers have only looked at the right end of the tub. We've ignored normal life and focused on end of life. So, what's an engineer to do if she designs a big capacitor bank with, say, 20 aluminum electrolytic capacitors connected in series-parallel, and her boss asks, "How many capacitor banks are going to fail in the first five years?" Until now she would have to say, "Well, the CDE Screw-Terminal Life/Temperature Calculator says they won't start wearing out until after five years, but I don't know the failure rate before then.

But now it has all changed. The CDE life/temperature calculators also calculate failure rate during normal life. So the engineer, after reading Reliability of CDE Aluminum Electrolytic Capacitors by Sam G. Parler, Jr., P.E. and a little math, would look very smart and tell her boss, "For the capacitors the MTBF is 5.08 million hours and the failure rate is 197 ppm/kh. So in the first five years with 1000 capacitor banks in the field and an average ambient temperature of 65°C we have a 60% probability of having only two bank failures."

She would get a promotion and her 10% raise and Cornell Dubilier would have another satisfied customer all because it was first to furnish a convenient tool for calculating reliability during normal life of aluminum electrolytic capacitors. It's a story worth repeating.