[sdiy] judging a cap's age - a troubleshooter's conundrum

[Harry Bissell Jr]

Size vs voltage rating of a capacitor is
not a good indication of age.


A cap that is intended for a high ripple current
application WILL be larger (as a general rule) than
a general purpose cap... even with the same microfarad
and voltage ratings.

I would look for things like company logo or
markings that are known to have changed over time.

H^) harry

--- anthony <aankrom at bluemarble.net> wrote:

> When I was working on my R-870 I noticed marks on
> the PC board for cap 
> polarity orientation suggesting that the
> electrolytic caps had been perhaps 
> recently changed.
> 
> I looked and they were Nichicons, a brand I like
> (though not as well as 
> Rubicons and some of the Panasonics oh and I like
> Elnas too...) so I didn't 
> look super close at first until I had to search for
> a specific capacitor 
> that had failed (I discovered) and it was quite
> obviously the original unit.
> 
> Then upon closer inspection of the electrolytic caps
> all over the unit I 
> noticed that although they were Nichicons, they were
> OLD Nichicons: 
> 10uF/16V. A newer one that size would be 50V. At
> least that's the usual way 
> I age caps. I know scrapping old and used caps is a
> dodgey venture, but I 
> have a big pile pile (tub really) of pre-1990 caps
> and then the others are 
> sorted out into drawers.
> 
> So I pose this question: Is judging a cap's age by
> its voltage rating a good 
> rule of thumb? It seems so to me at firt blush, but
> I always find - almost 
> always in some sort of switching supply, a largish
> for its value/voltage 
> cap, usually colored red. Do these have some other
> special rating that makes 
> them more suitable for a critical part in a
> siwtching supply? Like ripple 
> current or something?
> 
> I suppose this info is really only useful to myself
> since I'm probably the 
> only one who bothers to look at every single
> capacitor he scrounges very 
> carefully, judging its appearance and specs and name
> brand and comparing 
> date codes. (I wish I could actually read them.) Any
> sign of gunk around the 
> leads and it's tossed. "Spherical" caps get thrown
> out too - like the 
> 220uF/400V Daewoo I threw away the other day and
> wondered what it would look 
> like if I took my high voltage power supply outside
> and slammed it (the cap) 
> with reverse polarity. I've noticed more bulges from
> Daewoos than any other 
> high voltage cap, giving me a generally poor opinion
> of all Daewoo caps so 
> they get chucked into the BIG bin. I only actually
> trow away caps that I'm 
> afraid might actually spontaneously pop open like
> the aforementioned Daewoo. 
> I know that if I'd turned on the monitor that this
> cap had been in it would 
> have blown instantly.
> 
> And I know that a lot of  you guys think that buying
> new caps is the only 
> way to fly, but really how NEWis that "new" cap you
> just bought? How do you 
> tell? Like I bought some 10uF/50V caps a while ago
> that were big and fat and 
> I figured they were kind of old but I didn't care.
> But they were Rubicons 
> with a translucent yellow label which I think is a
> unit with higher ripple 
> current rating. And quite frankly unless you stick
> to really good brands, 
> new caps are often junk from the day they were made.
> I have some high 
> voltage caps from tube gear that are at least 40
> years old and they still do 
> their job quite well. I like it that plastic film
> caps are getting smaller 
> and smaller. I like it that a 0.47uF poly cap can
> take up almost the same 
> footprint as its electrolytic counterpart (but not
> really on a crowded 
> board) these days.
> 
> If you've made it all the way to this point: welcome
> friends!
> 
> ciao 
> 
> 
>