robb said:
i am working on an old mid 80's circuit board that has some
original 2200 uF/ 63V electrolytic caps (size of a C-cell) plus
some others and was just wondering when one should just replace
such a creature ?
says made in W-Germany "Elkorauh" if it makes a diference ?
should i remove and test them (maybe stress them ?) or just leave
them alone (i.e. fix broken things)
is there a life expectancy for electrolytics ?
First off, "Elko" is short for "Elektrolytkondensator" (electrolytic
capacitor), and "rauh" ("rough") refers to the electrode type. This
kind of etched electrodes is standard; they result in higher
capacitance per volume, while plain electrodes mean better behavior at
high (i.e. upper audio) frequencies. And, generally speaking, you can
expect electrolytic capacitors from Germany to be of high quality
(i.e. to be comparatively long-lasting).
The life-time of electrolytic capacitors is primarily linked to
electrolyte loss (i.e. evaporation) over time, which strongly
correlates with ambient (storage or operating) temperature; it further
depends on the quality of the seal, and on the (initial) amount of
electrolyte they are meant to contain - larger capacitors can
therefore be better than miniaturized ones.
According to their expected use (e.g. consumer versus industrial
products, room temperature versus elevated temperatures), electrolytic
capacitors are sold in different "endurance classes" which can be
inferred from the labeling. The cheapest (consumer quality)
electrolytics are typically rated >2000 hours (three months) at 85
degrees centigrade. However, even this usually translates into >300000
hours (thirty years) at 30 degrees. And still significantly longer at
really convenient room temperatures. Industrial quality electrolytics
(rated >2000h at 105°) can be expected to last at least twice as long.
Thus, at normal ambient and operating temperatures, even standard
electrolytics can be expected to last a human life. Smoothing
capacitors in power supplies that are noticeably heated up by the
ripple currents they are expected to short-circuit, or by adjacent
transformers or heat sinks, are usually more endangered. Unless your
board is operated at elevated temperatures, or is safety-critical or
would be hard to service because it will be installed in an
inaccessible place, a prophylactic replacement after 20 years would
usually seem unnecessary.
Martin.