Eric Smith wrote:
"Michael J. Mahon" <mjmahon@aol.com> writes:The typical failure mode of electrolytics is progressive loss of capacitance, so there is no catastrophic effect of this failure, just a progressive loss of performance.The loss of capacitance is just the beginning. The oxide layer (dielectric) breaks down, reducing the effective voltage rating of the capacitor as well. Eventually it gets to the point that a voltage well below the rating will punch through the remaining dielectric, making it (briefly) act like a dead short. This basically happens when the electrolytic sits unused for a long time. The time varies depending on the exact construction and materials of the capacitor, but usually takes longer than five years of non-use.
<snip interesting description of reforming technique> The problems of "starting up" long-idle electronics is an interesting problem, but not the one that I was addressing. In fact, I have simply turned on a lot of monitors that had not been operated for at least ten years, and have never (yet!) experienced a failure when doing so. Perhaps capacitors have improved in the last 25 years, or perhaps most "idled" capacitors can be reformed to their working voltages in seconds. I just know that it hasn't happened to me. (BTW, it *has* happened to me with older equipment stored for, say, 30 years--electrolytics used to be much more unstable, and 30 years is a long time. ;-) The problem I *was* referring to is the loss of capacitance brought on by prolonged operation at a relatively high temperature. This causes electrolytics--which are all non-hermetic to allow for venting--to show increased internal resistance and decreased capacitance, both of which diminish their usual function, which is to filter and decouple. -michael Music synthesis for 8-bit Apple II's! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it is seriously underused."