Prophylactic replacement of electrolytic capacitors?

On Jan 13, 21:27, Louis Schulman wrote: capacitors. When these go bad, they can 2000 hrs., or a shelf life of ten years. I think you may have lost a digit off the working life, Louis, at least if you're referring to the sort of electrolytics found in PSUs :-) If it ain't broke, don't fix it. As always, there's an exception to prove the rule. If one of a pair goes, it may be worth replacing both to get the values to match. Or in some PSUs, if one or more fails, they may all have got too hot or dried out, and at least for small ones (relatively inexpensive), I tend to replace the lot. In any case, check the others, they may be on their way to join it. The working life is an estimate based on mean time between failures (MTBF). All this says is that for a large sample, it is statistically likely that a certain proprtion will fail in a certain time. Variation can be enormous. Depends. The more expensive ones may differ in a few ways: -- lower ESR and/or higher ripple current tolerance. This means they won't waste so much energy (and heat up) if used in a PSU delivering a high current. -- higher temperature rating. PSUs often get rather warm, and the higher temperature rating makes them less prone to drying out. -- longer working life (related to temperature and other factors). If one can't find the right value in the right Electrolytics often have a wide manufacturing tolerance. -20%+50% is still not unusual. If it's just a filter capacitor I'd say up to 2x is acceptable. The real issue is likely to be cost. Also bear in mind that a capacitor of the same size but a higher capacitance may have other differences, like ripple current rating. I recently replaced a pair of 7700mfd caps in a DEC PSU; I could only get 10000mfd in the right size. In capacitor terms, that's close enough to be considered a match. Yes. -- Pete Peter Turnbull Network Manager University of York