22 Jul
2015
22 Jul
'15
4:36 a.m.
that are
running perfectly "just in case"...
How do you -know- they are "running perfectly"? Just because a widget
itself is functioning, you have no way of knowing if that capacitor is
working 100% properly /unless/ you actually remove it from circuit and run
a full battery of tests on it. Simply measuring the capacitance with a DMM
while a capacitor is in circuit isn't good enough. Given that a typical aluminum electrolytic capacitor
costs anywhere from
$0.12-$0.15 (4mm or 5mm diameter radials) to about $1.00 (12mm or 16mm
diameter radial), it also doesn't make much sense to desolder a 20 year
old part, spend at a minimum 5 or more minutes testing it, and then solder
it back in. It it much more economical to pull the old part and install a
new one and be done with it. (You also don't have to worry if the
desoldering and resoldering process might have damaged the original parts
end-seals.) That said, I personally pre-test new parts, in bulk, before I
I don't remove parts unless they have something to do with the problem I am
solving. If the power rails are the right voltage with sufficiently low ripple then
I look elsewhere for probkems.
put them into my stock, so I know ahead of time that
I'm installing
known-good parts.
You claim that electrolytics deteriorate with time whether used or not. How
do you know the ones you install haven't deteriorated since you tested them?
On many occasions I've cut open old aluminum
electrolytics, and the guts
very much do deteriorate with age. In addition to corrosion of the foil
(black spots and pitting) and foil to terminal junctions (corrosion), one
thing I particularly noticed was the more operating hours an aluminum
electrolytic capacitor had on it, the more its electrolyte and paper
insulator tended to smell bad compared to an otherwise identical (same
brand and series) part that had very low hours. These are all clear signs
of deterioration.
Firstly the paper is not the insulator. After all, it is soaked in electrolyte. And
'smell bad'??? OK, so some chemical change has taken place, but how do you
know it is detrimental to the performance of the capacitor?
-tony