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85 C Electrolytic capacitors life

Discussion in 'General Electronics Discussion' started by davelectronic, Aug 29, 2011.

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  1. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Hi all.
    I have been googling round to try and estimate an 85 Deg C, 35 volt 2200uf electrolytics capacitors life span, i can only get approximates in time.
    I was trying to work out the life of the capacitor in a very small power supply.
    Detail, power through or drawn from the supply, 350ma standby for 18 hours a day, but in those 18 hours a day the current draw increases to 1.2 amps for 15 minutes 3 times in that 18 hour period, so 45 minutes of 1.2 amps in the 18 hours.
    The rest of the time the units off, the other 6 hours, making up the 24 hour day.

    The voltage is a constant 13.50 volts, the capacitor is in an environment of a temperature of 40 - 50 Deg C, at peak current times 50 C and at standby about 40 C .

    All i can find is max hours at max working temperature, not much help in determining its life span, the input voltage after rectification and the capacitors filtering is 19 volts, does or can any one give me an idea on it life span, approximately, ok why bother, well i am going smaller and smaller with a psu design, the capacitors environment is becoming small, and as a rough idea i was looking to find out the life of the capacitor, going on the above basic statistics, if its possible to work out a rough estimate of its life.

    Its being used in an audio communication power supply. Dave. :) PS any ideas would be valued as a design guide for future projects, if the unit needs to be seen i can upload a picture of the psu.
     
  2. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Did you try to Google capacitor life(time) calculator? I got 64000 hours (10 years), not including the reduced ripple current, - starting with 2000 hours rated life.
     
  3. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Capacitor life

    Good evening Resqueline.
    No not tried that curious i will have to have a look now, thanks. Dave. :)
     
  4. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Capacitor life

    Hi again Resqueline.
    I got 1216 hours, thats a little over 50 days, unless i filled out something wrong, i don't think i did, the site i used is below the numbers from top to bottom i put in where 19 35 14 85 35 and got the above results. Dave. :)


    http://www.illinoiscapacitor.com/tech-center/life-calculators.aspx
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    The life of the capacitor is pretty much determined by the temperature.

    And the temperature is determined by a combination of the ambient temperature and ripple current/ESR. Note that placing a capacitor next to a heatsink for something else is not good as it increases the ambient temperature around the capacitor.

    Another trap is the life at the max rated temperature. 2000 hours is a reasonably common standard, but I've seen 1000, 500, and even 250 hours for some surface mount devices.

    If the temperature of the capacitor under full load does not exceed ambient by a significant amount, then go with ambient temperatures, otherwise you may need to take operating temperature into account.
     
  6. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Capacitor

    Hi Steve.
    Yes its a bit above ambient about 36 to 40 Deg C so it might not last long, the unit, or this one could have an axial fan in it, but i opted not to use one on this psu, i can get fans as small as 20mm or a little smaller, its about the size of a pocket box of matches, the heat sink is a chip set cooler, passive.
    I wanted to use a 35 volt 4700uf electrolytic, but could only fit a 35 volt 2200uf in the tight space, oh well it lives as long as no one says there is no mains hum, i am playing at others a little bigger, they have 40mm axial fans in. Dave. :)
     
  7. davenn

    davenn Moderator

    13,866
    1,958
    Sep 5, 2009
    ok so on that calc site the first thing it asks for is L1 - Load Life Rating

    so what is Load Life Rating ?? how do you work that out ?

    Dave
     
  8. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    That's the site I used too, but the numbers I put in were 2000h 35V 13.5V 85C 45C
    I don't understand why you put 19 (whatever) there.

    I expect "Load Life Rating" to be the full load life rating you (always) find in the datasheets. You have to put hours into a formula to get hours out.
     
  9. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Capacitors life

    Hi all. I thought load life rating was the max voltage from rectified and filtered voltage which is 19 volts. I did not think it was a time number, so ive got that bit wrong, i will try again when putting the pc on later, thanks for all your replies. Maths was never my strong point, i can do most of the maths in working out circuit parameters, but get hung up on some of the complex equations and formula. Not a crime, just not my strong point. Dave.
     
  10. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    I noticed the mention of a 19V somewhere, but that was across a different capacitor than the one in question here, and is therefore a different calculation.
    You don't include your neighbours income in your own tax report, ;) but I know feeling uncertain easily makes one overcomplicate matters. :)
    The 2000 hours I used is just a common lifetime number. It could be anything from 1500 to 4000 hours (or more) for your capacitor.
     
  11. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Capacitor life

    Hi Resqueline.
    There are only four capacitors in the circuit, two decoupling ceramic disk, and two electrolytic, one is the main filter capacitor 35 volt 2200uf radial electrolytic 85 Deg C, the other electrolytic is 25 volt 100uf radial electrolytic 105 Deg C, the capacitor iam looking on life at is the biggest filter capacitor, i altered the life load to 2000 hour as a guesstimate, its thrown up a lot longer, 83,364 hours, i only ever started with the one main filter capacitor, so the numbers where put in to the link site below as, load life rating 2000 hours, maximum voltage rating of the capacitor, 35 volts, operating voltage of the capacitor, 19 volts after filtering, maximum temperature of the capacitor 85 Deg C, and ambient temperature of the capacitor, in its working environment about 40 Deg C, these are the numbers i put in to get 83,364 hour from the calculator. Dave. :) PS the numbers i entered from top to bottom where, 2000, 35, 19, 85, 40, in that order. to the calculator in the site below.

    http://www.illinoiscapacitor.com/tech-center/life-calculators.aspx
     
  12. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Capacitor life

    I put 19 volts as operating voltage operation number, as this is the filtered voltage, not the regulated voltage, as i thought it means the voltage the capacitor is working at, 19 volts from filtering. Dave. :)
     
  13. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Capacitors life

    Hi again Resqueline.
    Your post in between the last two of mine has gone, the one that says operating voltage of application ? not sure where that post went . Dave. :) PS Sorry my mistake its on page 1. Any way it looks like good news, better than i thought.
     
    Last edited: Aug 30, 2011
  14. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Capacitor life

    Any way my only query is the operating voltage of the application, is it 19 volts the filtered value, or the final out put regulated voltage, 13.5 volts, for this input value to the calculator. Dave. :)
     
  15. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    It's not easy to follow you, but as far as I understand now you have a 2200uF 35V 85C main filter cap' with 19V across it, and then a 100uF 25V 105C output cap' with 13.5V across it.
    2000, 35, 19, 85, 40 are appropriate numbers for the first (input) cap', and 2000, 25, 13.5, 105, 40 would be appropriate numbers for the second (output) cap'.
    Keeping each part separate makes it much clearer (for everyone). In this regard the output voltage has no impact on the input cap' and vice versa.
    83000 hours for the first cap' sounds quite sensible.
     
  16. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Capacitor life

    Hi again. I thought it was obvious as the filter capacitor was the largest in uf value, appolagies for not putting it more clearly in my posts. Its a simple typical VR psu circuit, filter capacitor 35 volt 2200uf electrolytic, two low value decoupling ceramic disk capacitors, and 25 volt 100uf output electrolytic capacitor. Any thanks for all the members replys, and working out my ? Thanks to all. Dave.
     
  17. davelectronic

    davelectronic

    1,087
    12
    Dec 13, 2010
    Life of a capacitor

    Hi all.
    just a small picture of the box the 35 volt 2200uf capacitor i had concerns of it life lives in, the small unit on top, 13.5 volts 2 amps i doubt it could reach that before thermal shut down, but it might, it only drives i radio, RX 350ma TX 1.2 amps. Dave. :)

    [​IMG]

    The lower box is the transformer, 30 VA 15-0-15 air cooled 40mm axial fan run at 5.2 volts. cooling due to max transformers current draw, the transformer has 130 degrees C thermal fuse non reset, so the enclosure is tight very little room hence air cooling.
     
    Last edited: Sep 1, 2011
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