Prophylactic replacement of electrolytic capacitors?

From: Jerome Fine <>
Date: Mon Jan 14 12:18:36 2002

>Pete Turnbull wrote:

> >On Jan 14, 9:45, Jerome Fine wrote:
> > Also, more specifically, I have a number of BA23/BA123 boxes
> > which are about the only PSU I am concerned about for the long term.
> > Most are probably more than ten years old already - as far as shelf life
> > is concerned. Is a PSU (in general an very specifically a BA23/BA123
> > box) more likely to have a longer shelf life of used every so often - any
> > if so, how often - once a week, month, year, decade?
> That will make a difference, as electrolytics tend to degrade over time.
> The insulator is really a thin layer of oxide on the metal foil inside,
> and if left sitting unused, that may dissolve. Hence the low shelf life.
> That's why you run long-unused electrolytics at a low voltage for a while,
> to reform the oxide layer. Running the PSU every so often -- once or twice
> a year -- will prevent that happening. With a linear supply, running it at
> low voltage is not too difficult -- if there's no variac handy to reduce
> the voltage, a low wattage (but mains voltage!) light bulb in series is a
> good idea. That's not a good idea with switchers, because they just try to
> draw more current instead, which is often worse. The ideal solution is to
> remove the caps and run them on a current-limited bench supply, gradually
> winding it up from a low voltage to the rated voltage of the capacitor.
> The PSUs in BA23/123 (almost all QBus machines, in fact) are switchers,
> BTW.

Jerome Fine replies:

OK! I get the point. I should turn on the BA23/BA123 boxes at least once
a year. Now, what if they have been off for 5 years? I am useless with a
soldering iron. Is it better to just go through every box and put in a reasonable
load ASAP or leave them unused?
Received on Mon Jan 14 2002 - 12:18:36 GMT

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