Recycling capacitors, where do you draw the line?

[Evil Lurker]

Ok it seems as of late I have a pretty decent supply of junker computers. K7's and various P4's. Needless to say, just about all of them have bad caps.

Anyhoos, today I finally got my Blue ESR meter built, calibrated, and all that good stuff. And lemme tell ya, that thing is better than sliced bread for snffing out bad capacitors! I honestly don't see how anyone can even begin to repair modern electronics without one.

Back to my question... I see on some junker PSUs that the average
low ESR caps they are using for output filtering typically reads anywhere from 02-.04 which in most cases is above the manufacturers specs. Obviously I'm assuming that anything reading more than .05 is probably on the way to the graveyard if it isn't already there.

But, alas the meter does not have sufficient resolution to really measure that
low, and I'm also guessing that once you get down into that range there is some error on the part of the meter that can't be helped.

Since these systems and PSUs are free, and the PSUs are old revision ATX styles typically biased towards the 5v rail with low 12v amperage ratings, I don't want to sink any money into them if possible. Now if I run up on a more modern PSU with a couple 12V rails, thats diferent, I would probably do a full recap of it. Basically all I want with the typical trash picked junkers I find is to get them to work and run stable, at least for a while.

Thoughts?

[Th3_uN1Qu3]

Re: Recycling capacitors, where do you draw the line?

If it looks good on the scope then it is good. If you don't have a scope... well, save some more money and get one.

[Uranium-235]

Re: Recycling capacitors, where do you draw the line?

I just set my meter to ohms and if it has a good resistance curve I'll use it...ONLY as long as its good and ONLY as long as its: Rubycon, some Nichicon, Panasonic, Sanyo, Polymer

[Evil Lurker]

Re: Recycling capacitors, where do you draw the line?

A scope is definatly on my list but its probably going to be several months off in the future before I can afford one. Then I'd have to figure out how to use the darn thing.

Heck, as far as I know for all intents and purposes I got about as much expertise in and funding to devote to studying electronics as Mexico's space agency has towards putting a man in orbit.

In the meantime what I'm attempting to do is to try and locate as many duplicate components as possible, test them out the best that I can, look for patterns in the results to compare against known good components, compare datasheets to find suitable cross references, and finally light the fuse in my decomissioned grain silo filled with sugar and potassium nitrate and hope it makes it off the launch pad without blowing up.

[999999999]

Re: Recycling capacitors, where do you draw the line?

You are going to too much trouble. If a cap has failed, replace all of same type in that subcircuit. If others haven't, leave them, no need to test their ESR because as you wrote, you don't want to sink money into them as they are aged low value systems. Yes some capacitors will have drifted higher in ESR than spec'd. Some might have started out higher, and some will still be low enough to filter sufficiently in the circuit. When they are a problem on low value systems is when the ESR decays enough to cause a burst failure, before then it is very rare to find instability from an intact capacitor because other components downstream also have capacitors relative to their current needs and noise immunity per part.

If you factor that the whole system might be worth $100, then divide that by the relative value per part, you'd be spending significant time and expense to re-cap a PSU that isn't failing yet with it being worth very little to someone who isn't relying on it as their primary use system(s).

An exception would be if you are setting one up for something more important such as a 24/7 home NAS, then I'd replace all the output PSU caps knowing that the system would be in service long enough (enough hours total) that they'd all likely fail before that period elapsed unless they are unusually high quality caps (on average, you won't find most random systems have enthusiast level PSU in them so they'll tend to have budget grade capacitors).

[Longbow]

Re: Recycling capacitors, where do you draw the line?

Anyhoos, today I finally got my Blue ESR meter built, calibrated, and all that good stuff. And lemme tell ya, that thing is better than sliced bread for snffing out bad capacitors! I honestly don't see how anyone can even begin to repair modern electronics without one.

Yes, I wish I had one back in the day! I love mine!

Back to my question... I see on some junker PSUs that the average
low ESR caps they are using for output filtering typically reads anywhere from 02-.04 which in most cases is above the manufacturers specs. Obviously I'm assuming that anything reading more than .05 is probably on the way to the graveyard if it isn't already there.

I wouldn't be so quick to toss them. All caps will slowly degrade over time, but that doesn't mean they aren't useful parts. Consider also that many of them are costly and have a unique form factor. Its a judgement call based on the manufacturer of the cap and known track record, if any. That's why keeping a 'boneyard' is so handy.