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What is the expected lifetime for an electrolytic capacitor?

Discussion in 'Electronic Repair' started by [email protected], Mar 22, 2007.

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  1. Guest

    I'm wondering what the expected lifetime is for electrolytic
    capacitors in recent years. I'm sure temperature and operating
    voltage play a role.

    The reason I'm asking is that I recently replaced the electrolytic
    capacitors in the power supply of a 23-year-old Fluke signal generator
    I own. One of them was "bulging" so I replaced all the large
    electrolytics in the supply, and for good measure, the tantalum ones
    as well. The supply voltages are now cleaner.

    There are a number of other electrolytics on the various circuit
    boards in the synthesizer. I've already replaced a few of them as a
    precaution, e.g. 16V, 220uF caps across +/-15V supply lines. However,
    all the others are operating well below there rated voltage, and I'm
    wondering if it's worth replacing them while I have the synthesizer
    apart.

    -Dave
     
  2. Guest

    It varies hugely. Some have lives of thousands of hours, some of over
    a century.

    Ripple current also affects them.

    Capacitors failng to do the job are often not down to bad caps, but
    rather bad design with insufficient margins.

    I'm no fan of replacing good caps with other good caps that are just
    as likely to fail, but if you've found bad caps in there then any
    others the same make are probably best replaced.


    NT
     
  3. On many consumer goods *all* the electrolytics are the same make. I'm not
    in favour of the shotgun approach unless you are certain there were batch
    etc problems at manufacture.

    Coincidentally, I've just fixed four identical radio tuners all with the
    same fault. They were installed in a hotel and were on 24/7 power, and all
    failed within a short time of one another. The fifth one strangely still
    works ok.

    The fault was a 22µF 63v electrolytic which is in series with one
    transformer winding and that rectifier followed by a voltage regulator.
    Dunno why they used this rather strange - to me - arrangement. Three were
    open circuit on my ESR meter - the fourth read 55 ohms. It took some
    finding as the output from the (discrete) voltage reg circuit was 5 volts
    instead of 30 and not being able to read the zener value without removal I
    assumed 5 volts was the correct amount...
     
  4. Guest

    No.
     
  5. Guest

    OK
     
  6. No need to guess-- go to the digi-key catalog and look at the specs.
    The lifetimes are a heck of a lot shorter than you might expect.
    -- just a few thousand hours at the "rated" temperature.

    Then again some of us have 65 year old tube radios with the original
    electrolytics.

    The only way to tell is to measure each dang one with a cap or ESR
    meter. For example many Tek 22xx series scopes need new PS capacitors
    as the original ones were of marginal quality. And many small caps,
    under 10uF, have dried out much faster than the larger ones and now
    are more like resistors than capacitors.
     
  7. A? (as in "Canadian, a?" - ducking now! eh?)

    John :-#)#
    --
    (Please post followups or tech enquires to the newsgroup) John's
    Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call
    (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
    www.flippers.com "Old pinballers never die, they
    just flip out."
     
  8. mike

    mike Guest

    I recently came to a sad realization...I'm gonna have
    to quit buying (newer) old equipment with the expectation of fixing it.

    Was an HP LCD monitor. The cap on the output
    of the swticher had failed putting 20V pulses on the
    5V supply line. Fixing the cap didn't help 'cause
    the 20V had taken out the control processor and who-knows-what-else.

    Switcher designs I've seen use the cheapest available components and
    have no prevision to limit voltage when the output cap opens...and given
    the extreme stress placed on it by the switcher, it will...eventually.

    I predict this time bomb is gonna have a profound impact on the
    used equipment market.

    mike
     
  9. PeterD

    PeterD Guest

    "Who opened the door?"
    "I"

    shortest sentence solved!
     
  10. Guest

    A good point, and one I've become mindful of as I've crawled around
    the insides of the Fluke signal generator. It's full of rare
    integrated circuits, and I imagine some were designed for production
    of that specific instrument. Replacing caps is no big deal, but if any
    of those chips go south, I'm probably screwed. I suppose I could
    attempt to order replacements from those idiotic sites--the ones you
    find using Globalspec.com or any of those other annoying search
    engines--but I've read that they only deal with industrial buyers that
    purchase in large quantities.

    -Dave
     
  11. James Sweet

    James Sweet Guest


    Lifespan is determined by too many factors to predict. Capacitor
    quality, temperature, circuit characteristics, it can range from months
    to decades.
     
  12. Arfa Daily

    Arfa Daily Guest


    ??????????? Isn't that rather what I was saying in that thread last week,
    when you were contending that a 40v cap is good to 40 volts long term, and
    implying that by saying anything different, I did not know what I was
    talking about? Sorry to bring it up, and I really don't want to start all
    that up again, but I was gobsmacked when I read what you now seem to be
    saying ...

    Arfa
     
  13. b

    b Guest

    I think some just fail with age and lack of use too, then fail when
    voltage is reapplied. Last week i repaired a portable cassette
    recorder with extremely noisy hissy output with the programme material
    almost inaudible. there were two caps, a 220uF and 100uF 16v I think ,
    across the output stage of the amp. Both were within operating
    voltage, looked fine no bulging etc. but this machine had been sitting
    for decades without use.
     
  14. Guest

    You misunderstood what I was saying significantly, and following your
    last response I doubt there's any mileage left in the discussion.


    NT
     
  15. Both were within operating
    Classic "drying out" of electrolytics. No use needed. Heat speeds the
    process, but not required for the end result.
     
  16. Arfa Daily

    Arfa Daily Guest

    Yes, you are right that there is no further mileage in the discussion, and I
    meant what I said about not wishing to pursue it further, nor do I now, but
    I think that I have got to leave it this time by saying that if I
    significantly misunderstood what *you* were saying, then you for sure
    misunderstood what *I* was saying ....

    Arfa
     
  17. Andy Cuffe

    Andy Cuffe Guest

    As you said, it depends on a lot of factors. Temp, circuit design and
    the quality of the caps are more important. An ESR meter is very
    handy in cases like yours. It's not unusual to find a few totally bad
    caps when the rest are fine. On the other hand, I've seen plenty of
    cases where every last cap is bad.
    Andy Cuffe

     
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