30 Jan
2014
30 Jan
'14
12:33 a.m.
On 01/29/2014 03:57 PM, Eric Smith wrote:
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.
Early switching supplies did not deal well with the old high-ESR
electrolytics. Many failed dry simply because the electrolyte cooked
out from internal heating.
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.
That's true--I've carefully reformed old electrolytics on old radio gear
successfully. However, the approach of using a variac on a piece of
gear to run it at low voltage with an eye toward capacitor reforming can
be a grave mistake when switching PSUs are involved.
I'd venture that if the equipment was made much after 1980, you're
probably safe in throwing full line voltage on it and waiting for the
smoke to clear. You'll probably end up replacing a few tantalums anyway.
Your mileage of course, may vary.
I have no idea if the new conductive polymer aluminum electrolytics will
require reforming--and by the time that's firmly established, I probably
won't be around to witness it.
--Chuck