On Jan 29, 2014 1:50 PM, "Chuck Guzis" <cclist at sydex.com> wrote:
I'm not clear that periodically powering things on
does anything special.
If it perchance does, once every 20 years should do.
I think I'd recommend no less than every 5 years for the electrolytics, and
preferrably more frequently than that. I'd probably power up for a few
hours each time, if the equipment hadn't seen any other use.
I'll grant that reforming was a big issue in the
case of older wet
electrolytics, but drying out of the electrolyte in my experience
has been
more of a problem.
The drying out depends on the brand and vintage. If the capacitor was
sealed properly when manufactured, and hasn't been abused (electrically or
mechanically), it shouldn't dry out for many years. We had few if any dried
out electrolytics in the then 40-year-old PDP-1, but many that needed
reformation after only a decade since last powered operation.
As far as I know, modern aluminum electrolytics still work the same way, so
they are still prone to oxide breakdown. It's a fundamental characteristic
of the product, not a manufacturing defect, unlike e.g. a substandard seal
or an incomplete stolen electrolyte formula. At least one aluminum
electrolytic capacitor manufacturer had an app note about reformation on
their web site when we did the restoration.
The oxide breakdown is a progressive degradation, not a step function, and
different circuits (even in the same product) operate the electrolytics at
diiferent actual working voltages (as compared to rated maximums), so it is
difficult to give a one-size-fits-all rule of thumb regarding minimum
operating intervals and periods.