14 Jan
2002
14 Jan
'02
12:18 p.m.
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.