[time-nuts] Replacing electrolytics - any disadvantages of high temp ones?

Bill Hawkins bill at iaxs.net
Wed Jun 22 03:27:59 UTC 2011


Group,

During my days of interest in antique radios, I learned that
the dielectric between aluminum plates was formed by passing
current in one direction to build up an oxide coating on the
plates, which became the dielectric. The thickness is directly
proportional to working voltage and inversely proportional to
capacitance. As we learned from reforming old caps, the oxide
thins when there is no voltage on the cap, but can be restored
by passing several milliamps through the cap. Applying rated
voltage before it was formed would destroy the cap by welding
spots of the plates together.

I'm not sure that this applies to modern caps.

As to the temperature rating, a high temp cap run in a cool
environment will be as unhappy as someone transplanted from
Miami to Minneapolis in the winter. It may work, but it will
be very unhappy - so it depends on your empathy for the cap.

There ought to be a way to work precision time into this
thread, but I can't think of one.

Bill Hawkins


-----Original Message-----
From: Poul-Henning Kamp
Sent: Tuesday, June 21, 2011 2:40 PM

In message <4E008A73.50701 at erols.com>, Chuck Harris writes:

>and yet, I find that some electrolytic
>capacitors that have been run at lower than normal voltage improve markedly
>when "reformed" by applying  rated voltage through a 10K resistor for a
>couple of hours.

I noticed in a datasheet at one point, that the capacity only was
warranted above a certain percentage of rated voltage.  No explanation
was given.





More information about the time-nuts mailing list