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LED overvoltage life expectancy ques.

Discussion in 'Electronic Design' started by frenchy, Mar 23, 2007.

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  1. frenchy

    frenchy Guest

    If an led lamp is rated at 6 vac, and it's put in a circuit that duty
    cycles regular incandescants - it has a peak of 18 vac but the result
    of the cycling is the regular bulbs light as bright as if they were on
    pure 6 vac - question, roughly what percentage of life would be
    expected to be lost on that led over time? I mean, cut it in half, or
    more, or (?) Same question for a led rated at 12 volts too...
    thanks!
    Frenchy
     
  2. D from BC

    D from BC Guest

    Amazing..It's english and I didn't understand anything in the first
    pass.
    D from BC
     
  3. Guest

    Light Emitting Diodes aren't rated for AC at all, being diodes.

    If you're talking about a lamp designed as a direct replacement for
    an incandescent lamp except it has LEDs instead of a filament, it has
    other circuitry within that will strongly influence the answers to
    your questions.

    More data, better answers.


    Mark L. Fergerson
     
  4. frenchy

    frenchy Guest

    Yes these are direct plug in replacements for 44 and 555 bulbs. So
    they have built in resistors or whatever else is necessary in them.
    They are specified for 6 vac and I put them in a pinball that runs
    44s, but later found out the pinball doesn't run pure 6 vac to the
    bulbs, it duty cycles them with a peak of 18v. For a 44 the result is
    it still looks the same in brightness as pure 6 v, but sounds like the
    led is being overdriven in this cycling. So have gotten various
    answers from pinball folks that this will reduce the life of these
    leds.
    Thanks!
     
  5. Rich Grise

    Rich Grise Guest

    If the peak voltage across the LED is greater than the LED's absolute
    maximum rated voltage, then its life expectancy is zero.

    Cheers!
    Rich
     
  6. Rich Grise

    Rich Grise Guest

    If you plug one in and it works, it will probably continue to work for
    the rated life of the LED. If you plug it in and it blows, then its
    life expectancy was zero.

    Hope This Helps!
    Rich
     
  7. frenchy

    frenchy Guest

    If you plug one in and it works, it will probably continue to work for
    Yes they are working just fine. When I plug the same one into the
    pure 6vac section of the pinball (one used for general illumination
    that's straight off the transformer) it's actually a little brighter
    than the ones I have put into the voltage cycled 'feature lamps'
    section. So I guess I'm ok. I don't know what the maximum rating of
    the leds in these plug-in bulbs are, they are only rated for 6vac use
    so that's all I know, they are putting unspecified leds inside of the
    lamp casing. Thanks!
    Frenchy
     
  8. Rich Grise

    Rich Grise Guest

    Well, it's apparent they already have their own limiting resistor, and
    a reverse-polarity protection diode, so you should be fine.

    I've found that doing an experiment like this can be the quickest way
    to the right answer. :)

    Cheers!
    Rich
     
  9. Guest

    Agreed, particularly when the mfgr doesn't/won't say what can happen
    in these circumstances.

    Frenchy, if I were you, I'd worry about it and contact the mfgr.
    Plain incandescents are cheap and can handle spikes that kill LEDs,
    but LED bulbs are still kinda spendy to take chances with. For all you
    know the "feature" supply can also supply spikes that will kill your
    LEDs.

    If they won't say and you're confident the PS is safe, never mind.


    Mark L. Fergerson
     
  10. jasen

    jasen Guest

    that depends on the lamp.
    same answer.


    -

    Bye.
    Jasen
     
  11. frenchy

    frenchy Guest

    I'm only using a few of these leds in spots where vibration is killing
    the bulbs and/or where a lot of stuff on the playfield has to be
    disassembled to replace them. Bulbs are about a dime, and these leds
    are a buck, so not talking large $. The encouraging thing is that the
    color and brightness seems to be the same on the pulsed leds as when
    they are placed in the straight 6v. If they were a lot brighter or
    the color was being screwed up I'd worry more. They are still
    working.
     
  12. Terry Given

    Terry Given Guest

    I have worked on a number of LED replacements for halogens and
    incandescents. These have had little SMPS inside them, providing
    constant current drive (unless they had to be dimmable). and would work
    just fine in your app. Smash one to pieces, and see whats inside it. If
    its a rectifier and a resistor, there will be trouble. If there is more
    stuff it will work, and Rich's comment is spot on. A less destructive
    test is to run it from 6V and use eyeometry to measure intensity. then
    stick in pinball using HAM (Hairy-Assed Mess) "6Vac" and do comparitive
    eyeometry; if they look the same then its probably a constant-current drive.

    Cheers
    Terry
     
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