Electrolytic caps?

I used to work in electronics and have several large boxes of electrolytic caps in my lab. Does anyone still use them for anything? Is there even any electronics still being built in this country?

What type / voltage/ capacitance are they?

Its "forming" (technically "reforming" since it was already done once at the factory long long ago). You can do a web search on electrolytic forming.

Basically you feed it rated voltage through a big current limiting resistor -- what you're doing is restoring the aluminum oxide layer on the foil. There are a number of techniques for verifying that the forming is complete (vs. the cap being bad) -- basically when you think you're done you test with more than the rated voltage to see if the thing leaks -- if so, you scrap it.

I've never done it, but it's a common thing with tube-equipped boat anchors.

Hi, Joerg. I do, literally, have some 40 year-old aluminum electrolytics in my part bins.

What's the best way to "format" them?

...Jim Thompson

It's actually "reform". Here's a web site that describes the process:

Best regards, Spehro Pefhany

And that means what?

electrolytic

any

I don't recall, I'd have to go look. I have boxes of them all over the place in my lab, which still hasn't been unpacked since we moved.

Hello Watson,

Nah. I have some 40+ year old radios where the electrolytic caps are just fine. A couple times I actually did a resistor charge and leakage test just to see. They were nearly as good as new.

But sometimes when they had been in storage for decades they may have to be "formatted" slowly to get them used to the job of "being a capacitor" again.

Regards, Joerg

I read in sci.electronics.design that Joerg wrote (in ) about 'Electrolytic caps?', on Sat, 26 Feb 2005:

It took a long time to discover that sodium chloride (common salt) contamination was responsible for short life of aluminium electrolytic capacitors, simply because traces of salt are almost everywhere. So if your old caps have, by chance or design, a low salt content, they may well still be good.

The way I do it, which I thought was standard, was to gradually raise the voltage from zero over a period of minutes, monitoring for leakage all the time, and then leave it charged to the rated voltage for some time.

You can measure quite an increase in capacitance from doing this, even if the capacitor didn't test out as defective to begin with.

I prefer to go for "High density". :)

Actually, after you re-form the oxide layer with a limited current (

I read in sci.electronics.design that Michael A. Terrell wrote (in ) about 'Electrolytic caps?', on Sat, 26 Feb 2005:

Both residual leakage current and ESR are important, but for ESR you need some guidance on what is 'good' and 'bad'. It depends on a number of factors.

It means that caps made during certain time periods and some companies are prone to failure from dried out seals and depending on the electrolyte used, the cpacitors may neeed to be re-formed.

I try to find the OEM specs for the cap and check it with my Bob Parker ESR meter. Failing that, I compare the capacitor(s) to others on hand, or to the specs of similar caps from other OEMs.

I have been running about a 50% failure rate for new old stock and salvaged electrolytics over the last year. I did the tests to entertain myself while I couldn't work, and had nothing to do and couldn't get on line for a year.

I used to have a Sprague TO-6 capacitor analyzer to check capacitance and leakage. I'm thinking about designing a digital unit to replace it and maybe sell kits.

years

Depends on a lot of factors including how long they have set without being used, how long they have been used, how high a temp they have been exposed to, etc. And of course how well they were made. The old timers seem to be better made back then, and withstand the test of time better. But the stuff being made today isn't as well made, IMHO. Smaller size, les ofecerything, etc, means they don't last like they used to.

I just got thru replacing the main filter caps on two different HP PSes; both were dead and gone. In one case the PS was 40+ yrs old, so it's understandable. But 5 years is usually what they aim for. Hey, they're full of juice, don'tcha know.

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capacitor"

That's reformed, as opposed to the original forming. And even so, you may find that some of the juice has leaked, so you won't get the full rated capacitance, but just a fraction.

Personally, having played with electronics and salvaged parts since the early 1950s, I think the whole "reforming" thing is pretty much baloney.

It's true, sometimes if you take an old electrolytic that tests poorly you can get it to improve by using the "reforming" process. Often, however, the resulting cap will have high ESR, and will want to leak for a while every time you apply voltage to it.

I find that, in general, unless the leakage gets down to where it should be in not more than maybe 15 seconds, the reformed cap is going to "deform" spontaneously. There are some caps that will stop leaking over maybe 30 minutes, but if you test the rest of their properties you will often find that you now have an electrolytic rectifier more than a capacitor.

That is not to say that all old electrolytic capacitors are bad. I recently worked on an old Tek scope and the electrolytics with 1967 date codes were perfectly good. However, electrolytics used in HP equipment of the same vintage are almost always bad. I have some NOS capacitors that are fine, and I just tossed a bunch that weren't.

I also worked on a 1992 fax machine recently. Every electrolytic cap was leaking, both physically and electrically.

Test your old caps. Ramp them up to rated voltage while watch>

years

leakage

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capacitor"

even

years

It means that if the cap you are going to use is that old, you had better not assume that it has the rated capacitance at the rated voltage. So measure it and find out for certain.

Here, I have a huge case of these, for starters: