Re: Question for our electrical engineers

On Tue, 22 Jul 2008 07:33:59 -0700 (PDT), John Bigboote
<Bigboote.YPS@xxxxxxxxx> wrote:

On 21 Jul, 17:18, Dave Curtis <dbaudiot...@xxxxxxxxxxxxxx> wrote:

If they can be *safely stored* while charged, go ahead.

Well, that settles it! I should either store them charged, or
discharge them before storage!

There you go!

Thanks, guys (no sarcasm intended). Since there seems to be no
obvious, definitive answer (as long as the capacitors can't be
accidentally discharged with life-threatening results), I guess it
doesn't matter too much. So the verdict is... I'm not going to worry
about it.

We now return you to your regular bass programming,

-jb

Not quite yet.

Everything you might want to know about Al electrolytic caps:

http://chemi-con.com/u7002/toc_ms.php

From the "Guidelines" page, there is no verdict:

Storage

The electrical characteristics of aluminum electrolytic capacitors are
dependent on temperature; the higher the ambient temperature, the
faster the deterioration of the electrical characteristics (i.e.,
leakage current increase, tan d increase, capacitance drop, etc.). If
an aluminum electrolytic capacitor is exposed to high temperatures
such as direct sunlight, heating elements, etc., the life of the
capacitor may be adversely affected. When capacitors are stored under
humid conditions for long periods of time, the humidity will cause the
lead wires/terminals to oxidize and thus impairing solderability.
Therefore aluminum electrolytic capacitors should be stored at room
temperature, in a dry place and out of direct sunlight.

A voltage treatment/reformation process to electrolytic capacitors may
have to be applied after a capacitor has been stored for more than 2
or 3 years. If aluminum electrolytic capacitors are stored above room
temperature for long periods of time, the anode foil may react with
the electrolyte increasing the leakage current. After storage, the
application of even normal voltages to these capacitors may result in
higher than normal leakage currents.
In most cases the leakage current will return to normal
levels in a short period of time. However in extreme cases, the amount
of gas generated may cause the safety vent to open.

Capacitors that are stored for long periods of time should be
subjected to a voltage treatment/reforming process (Note 1) which will
reform the dielectric and return the leakage current to the initial
level. Leakage current increase during storage will vary with the
working voltage of the capacitors, normally in this order:

Low voltage capacitors < Middle voltage capacitors < High voltage
capacitors.

Note 1: In the reformation process the applied voltage is gradually
increased up to the rated voltage without exceeding the initial
specified leakage current of the capacitor. After reaching the rated
voltage, continue applying this voltage for 30 to 60 minutes.

.

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