Electronics > Beginners

Digi-Key Sold Me 7 Year Old Capacitors

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Stray Electron:
  Just as a guess, Digikey probably had to buy 100,000 parts to get the best price and it's going to take them YEARS to sell them all.

edpalmer42:
Glad they worked out for you.

Just to be on the safe side, I would have reformed the capacitors before using them.  High voltage capacitors can have their voltage rating drop just from sitting on the shelf.  A slow, current-limited charge to their rated voltage will safely restore them.

I recently fixed a power supply that used six 1000 uf, 200V capacitors on the input.  Since I had no idea how long it sat on the shelf, I unsoldered them and reformed each one seperately.  I noticed that one took longer to charge than the others.  I wonder what would have happened if I had just flipped the power switch.   :-//

Ed

KE5FX:

--- Quote from: Smoky on August 29, 2019, 10:02:59 pm ---
I heard that the original electrolytics in the Tektronix TDS 400 series scopes started failing within a year of production, and that's what concerns me about this capacitor purchase.


--- End quote ---

That was a bit of a special case.  Tektronix and many other manufacturers encountered terrible quality problems with capacitors around that time.  The problems were due to specific circumstances that have long since been ironed out.   (There were actually a few different waves of 'capacitor plague' that affected different components at different times, but in any case it's been a few years since we've heard widespread complaints of capacitor quality problems.)

I don't think you have anything to worry about.  As for inventory cycling, FIFO is the rule across pretty much all industries.  The newest parts don't go out the door until the oldest ones are sold.  Check the dates on the milk cartons in the back of the grocery store dairy case sometime. :)

Smoky:
Yes, anytime I replace any electrolytic capacitors, the repaired project is brought up incrementally and slowly on the Variac.

In the case of this SMPS, I brought the AC volts up slowly to 25 and let it sit there for three to five minutes while I check for any hot spots.

I repeated that until I reached the full 120 VAC.

edpalmer42:
It's not a good idea to slowly bring up the input voltage on a switching supply.  I've heard that sometimes they can get into a weird state where they self-destruct.  Linear supplies are fine.  The only thing I'd do with a switching supply is use a dim-bulb tester and an isolation transformer.

Ed

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