What happens when electrolytic capacitors 'dry out'?

The mechanism by which an electrolytic capacitor "dries out" is that the water in the electrolyte evaporates. This is just like the dregs in a bottle of beer drying out, only with quote marks (and without the mold).

This "drying out" happens because all common* electrolytic capacitors aren't hermetically sealed, and the electrolyte _does_ have to stay wet.

Electrolytic capacitors that don't dry out can lose their ability to withstand voltage, because the oxide layer on the aluminum gradually goes away**. When powering up equipment with high voltage electrolytics that have been unused for a long time the capacitors must be "reformed" -- do a web search for the procedure.

• I know wet-slug Tantalums, as produced for aerospace applications, are sealed -- I know of no aluminum electrolytics that are so constructed.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

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As the water in the electrolyte dries out the internal resistance (ESR

- equivalent series resistance) of the capacitor increases and renders it useless.

The following is a good explanation of what's happening:

Replace all the electrolytic caps in old equipment before you even power up the unit. A bad cap can do more damage like fry coils etc.

Tom

Thanks for all the help and PDFs, everyone.

Quick question- Does use or lack of use have any effect on how soon caps dry out? I.e, should I power up all my amplification devices at least once a month or so as a preventative measure?

thx

-phaeton

"phaeton"

** Time and ambient temperature are the causes.

But most electros last a couple of decades, just fine.

** Lack of use and storage in damp places *damages electronics*. Condensation forms on metal parts and initiates surface corrosion and rust spots. All connectors, pots ad switches are damaged by this.

Electro caps can "depolarise" after a long period in storage, then overheat and fail when the item next turned on.

Occasional use is best, plus storage in a warm, dry environment.

...... Phil

Heat causes the seals do dry out and fail.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

the elctrolyte inside between the foils that comprise the two "plates" actually has a liquid that dries out over time. they are usually sealed well enough to last 20-30 yrs, but beyond that it is very iffy and prone to catastrophic failure (short) or in some cases they act like no capacitor exists in their place. (open)

some are actually "vented" to prevent bursting the can, (they make quite a mess of things when they do explode too!) if overvoltaged or heat makes them fail.

my uncles old 1920's RCA radio (36 inch x 20 inch x 20 inch behemoth) actually had brilliant chrome plated steel covers over each can capacitor and tube.

they just have a "lifetime" and will eventually fail. this is really old stuff u must remebr, way before xixtors and micropowered amps.

Yup, built in obsolescence. Just install a few near a heated area so that you can buy a new MB later on because every knows with in a short time, MS will have your MB hogged down any ways.

What marketing tactics.

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Where would YOU put them? On the opposite corner of the MB? They are close to the CPU's voltage regulator and CPU, because the HAVE to be. Trace inductance and resistance would make the CPU unstable if it wasn't right next to the CPU.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

The biggest problem I have found with electrolytics is they go short circuit blowing the fuse.

No Microsoft here.

-phaeton