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when (time frame) to just replace old electrolytic caps ?

Discussion in 'Electronic Basics' started by robb, Oct 25, 2007.

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  1. robb

    robb Guest

    i am working on an old mid 80's circuit board that has some
    original 2200 uF/ 63V electrolytic caps (size of a C-cell) plus
    some others and was just wondering when one should just replace
    such a creature ?

    says made in W-Germany "Elkorauh" if it makes a diference ?

    should i remove and test them (maybe stress them ?) or just leave
    them alone (i.e. fix broken things)
    is there a life expectancy for electrolytics ?

    thanks for help,
    robb
     
  2. We work on a shelf life of 10 years before needing reforming, assuming optimum
    ambient temp etc etc.

    In service on continuous operation about 20 years before we replace.

    We do refurbs on our older 30V switch tripping batteries and chargers, and we
    replace all the electrolytics and rectifiers, and the small transformer as well.
    Most of these come in when the batteries are at end of life, usually 7 years or
    so.

    Bigger systems tend to be less of a problem as the caps are bigger and better
    quality.

    Our preferred vendor was Philips/BC Components, but we are now using Rifa/Evox
    and BHC.

    Peter
     
  3. Jamie

    Jamie Guest

    Yes there is a life expectancy with electrolytics how ever, if you have
    tested these caps after some reforming time and found them to be ok,
    it may not be necessary to replace them..

    One a second note:
    If you're restoring, It might be a good idea to do so.
     
  4. Marra

    Marra Guest

  5. Guest

    First off, "Elko" is short for "Elektrolytkondensator" (electrolytic
    capacitor), and "rauh" ("rough") refers to the electrode type. This
    kind of etched electrodes is standard; they result in higher
    capacitance per volume, while plain electrodes mean better behavior at
    high (i.e. upper audio) frequencies. And, generally speaking, you can
    expect electrolytic capacitors from Germany to be of high quality
    (i.e. to be comparatively long-lasting).

    The life-time of electrolytic capacitors is primarily linked to
    electrolyte loss (i.e. evaporation) over time, which strongly
    correlates with ambient (storage or operating) temperature; it further
    depends on the quality of the seal, and on the (initial) amount of
    electrolyte they are meant to contain - larger capacitors can
    therefore be better than miniaturized ones.

    According to their expected use (e.g. consumer versus industrial
    products, room temperature versus elevated temperatures), electrolytic
    capacitors are sold in different "endurance classes" which can be
    inferred from the labeling. The cheapest (consumer quality)
    electrolytics are typically rated >2000 hours (three months) at 85
    degrees centigrade. However, even this usually translates into >300000
    hours (thirty years) at 30 degrees. And still significantly longer at
    really convenient room temperatures. Industrial quality electrolytics
    (rated >2000h at 105°) can be expected to last at least twice as long.

    Thus, at normal ambient and operating temperatures, even standard
    electrolytics can be expected to last a human life. Smoothing
    capacitors in power supplies that are noticeably heated up by the
    ripple currents they are expected to short-circuit, or by adjacent
    transformers or heat sinks, are usually more endangered. Unless your
    board is operated at elevated temperatures, or is safety-critical or
    would be hard to service because it will be installed in an
    inaccessible place, a prophylactic replacement after 20 years would
    usually seem unnecessary.

    Martin.
     
  6. Eeyore

    Eeyore Guest

    Good Lord ! I'd say that was very premature with 'typical' use.

    Graham
     
  7. Guest

    Indeed. It's all about evaporation and diffusion through the seal, and
    you can't discuss this without discussing temperature. Electrolyte
    loss more than doubles for each temperature rise of 10 degrees
    centigrade. For specific numbers applying to a quality product of the
    ">2000 hours at 105 degree" type see

    <http://www.epcos.com/inf/20/30/db/aec_07/B41851__B43851.pdf>.

    If you extrapolate the diagram at the top of page 19 to lower
    temperatures you easily arrive at life-times in excess of 100 years
    (10^6 hours) for low ripple-current loads.

    Martin.
     
  8. Pieter

    Pieter Guest

    Hmm. 5 years?

    I suggest:
    if it is "made in China" every 3 months
    if it is old Philips, and not used in high current or in a high
    temperature environments: 50 years or so

    I have several old radio's etc with original componnents from the 50's
    and 60's that still work perfectly. Not using them is bad. Use them
    and if they have not been used for years, format the caps at low
    voltage/current.

    Pieter
     
  9. Marra

    Marra Guest

    I run high power amplifiers that run quite hot so 5 years is a good
    time.
    I havent had any go short circuit yet so 5 years must be on the safe
    side.
     
  10. robb

    robb Guest

     
  11. robb

    robb Guest

    thanks for help and reply Jamie,

    now i need to go google reforming capacitor :)

    thanks for help
    robb
     
  12. robb

    robb Guest

    Thanks Martin.

    for all the useful info, now i can use your parameters to
    determine if replacement is needed.
    i think they will not need replacement because the stress level
    ( hours of usage, heat, etc..) is fairly low.

    these appear to be used in a stepper motor circuit and are placed
    far away from hot stuff

    i was mostly concerned about deteriorating from just age alone,
    but your info helps me relaize that capacitor age may not be as
    important a factor on the 20 year scale

    thanks again for all your helpful info,
    robb
     
  13. robb

    robb Guest

    thanks Pieter,
    i think these have average to low use and probably can be left to
    work for a few more years.

    thanks again for help and reply,
    robb
     
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