Donated electrolytic capacitors: keep or bin?

[tggzzz]

A local HackSpace has been bequested a large number of unused polarised electrolytic capacitors. My instinct is to bin them, but I wonder if I'm being unnecesarily pessimistic. Perhaps we should keep some and give spares to neighbouring HackSpaces - but I wouldn't want to knowingly give junk or waste our time debugging old capacitors!

Characteristics:

• mostly aluminium cans, with a few tantalum beads
• age unknown, but mostly "modern looking"
• storage conditions unknown, but no visible problems - in many small plastic bags in a big cardboard box
• range based on a cursory check: 10uF-2000uF, 6V-60V, ish
• many are in ziplock bags from well-known big distributors that are still in existence!
• a range of manufacturers, e.g. Rubycon, Philips, Dubilier, Ricon, Waycom
• briefly testing a few shows they have in-spec values

What are the likely failure modes, e.g. how would "drying out" manifest itself? Instant failure or failure after normal in-service lifetime?

So, keep, bin, or more tests? If more tests, then what simple quick easy tests could be done? I'm not going to spend much of my remaining life inspecting them, but I'll do a quick sanity check.

[T3sl4co1l]

Shelf life is generally considered something like 5 years; beyond that and they may need some reforming to rated voltage (normally, the symptom is a reduced voltage at which leakage increases sharply).  If they were stored under cool conditions, it's unlikely they've done much in that time, or dried out much (but they will be five storage-temperature-years shorter on whatever life specs they have).

I'd certainly keep them!

Tim

[German_EE]

ESR check them, maybe one per bag to get an idea of what state they are in.

[Seekonk]

If you will be pulling a half amp or more through them, I would take the step to reform.  Otherwise I would have no problem using them.  I recently used a 20 year old cap in a buck converter.  Due to a fault the cap was over voltaged for a while to the point it got quite hot.  Let it cool down and it has been running every day fine for three months.  Have a box of 30 year old no name 200uF and they still have have good ESR.  Sure I've replaced a lot of caps in my over 40 years of servicing but I don't know why old caps are getting such a bad rap.

[Conrad Hoffman]

I have lot of 20 year old caps that are fine after reforming. Look for a date code on the caps. It's usually a 4 digit code and two of the digits will be the year. 7426 would likely be the 26th week of 1974, but the codes may not be standardized. If the caps are more than 20 years old, I'd use them with caution. If less than 10 years, I wouldn't hesitate. High voltage caps tend to degrade a bit sooner and invariably need reforming with the current kept to a low value, maybe under a couple mA.

[MK]

The rash of capacitor failures from a few years ago was because a cap supplier stole the recipe for the electrolyte ffrom a competitor, but that competitor had found out and left a dud formula to be stolen, since that time the failure rates have come back down to more normal levels.

[SeanB]

Years ago I had a whole batch of 30 year old caps. Took a hundred and checked capacitance and ESR on them, then applied rated voltage through a 1k resistor for a half hour, then checked again. After the reform there was very little difference, so all I did was just use them.

If you just derate and only reform those you will be using at more than 70% of rated voltage then you should be fine. If they are good brands like indicated they will be fine. You might only have a few years of life at elevated temperature, but at under 40C there should be no difference.

[Seekonk]

I got this top of the line SONY VCR. Think they sold for more than $1,500 and it was like a piece of art.  At $7 couldn't pass it up.  They packed that switching PS so tight that every capacitor in it was open from the heat.  I had never seen anything like that before, a dozen caps all bad.  I took an angle grinder with a thin cutoff wheel to most of the shielding. Who cares about EMI, let the FCC try and find me!  There was plenty of room in the box to make the PS bigger.  Heat is a real killer.

[Alex Eisenhut]

I got this top of the line SONY VCR. Think they sold for more than $1,500 and it was like a piece of art.  At $7 couldn't pass it up.  They packed that switching PS so tight that every capacitor in it was open from the heat.  I had never seen anything like that before, a dozen caps all bad.  I took an angle grinder with a thin cutoff wheel to most of the shielding. Who cares about EMI, let the FCC try and find me!  There was plenty of room in the box to make the PS bigger.  Heat is a real killer.

SLV-R1000?

[SeanB]

Don't worry, Panasonic did the same. They did though make it easy to undo the can, so you could replace the 10 Rubycons inside that were always cooked from the light brown to black.