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Light dimmer

Discussion in 'Power Electronics' started by Christopher Alexandre, Dec 6, 2018 at 11:58 PM.

  1. Christopher Alexandre

    Christopher Alexandre

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    May 23, 2016
    When we use adjust a light bulb dimmer, if we increase the power from the minimum, the light will turn on at a certain point. But at this point, you can decrease the light power without turning it off. I know how a dimmer work but I can’t figure out why this happend. Could someone explaine me this effect?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Does this happen with bulbs that don't have a filament?
     
  3. Christopher Alexandre

    Christopher Alexandre

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    May 23, 2016
    This happens with incandescent light bulbs
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    One possible explanation is that the low resistance of the cold filament combined with other circuit elements that either limit current or limit the rise in current may provide insufficient heat to cause it to glow. Once the filament is glowing, it has a significantly higher resistance, and thus a given current will cause more heating in the filament. At this point it is possible to reduce the duration of the current pulses and maintain a high enough power dissipation in the filament to allow it to continue to glow.

    I have no idea if this is the correct (or if it is correct, the only) explanation, but I have noticed this behaviour and this *may* be a reason.
     
    hevans1944 and kellys_eye like this.
  5. CircuitMaster

    CircuitMaster

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    Dec 17, 2016
    Or if its intentional, it might be a histerezis. Like a Schmit trigger. The idea behind it is that it turns on at voltage "4VDC" (for example) and then while decreasing it turns off at "2VDC" (for example). However this only accounts for the ON and OFF, after its switched on something else regulates it. Otherwise I guess it can be some effect.
     
  6. BobK

    BobK

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    @Steve - I was thinking of the same explanation, but I saw your question and tried it out.

    It does happen on my dining room light, which has all LED bulbs, so filament resistance is not the answer.

    Bob
     
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  7. Bluejets

    Bluejets

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    Oct 5, 2014
    LED bulbs as Bob says will do this, even with a dimmer designed for general LED use.
    Bit of a nuisance but just have to live with it.
    I imagine there may be some underlying manfacturer reasoning but trying to find it is almost akin to flying to the moon.
     
  8. dave9

    dave9

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    Mar 5, 2017
    Might depend on the dimmer and you could try another one? Then again, how much work to put into optimal dimming for incandescent bulbs at this point? Dimmer, they're even less efficient, much much less.
     
  9. duke37

    duke37

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    Jan 9, 2011
    Maybe some temperature effect in the diac or potentiometer.
     
  10. Bluejets

    Bluejets

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    Oct 5, 2014
    Dimmers are not like they used to be with a simple pot,diac and triac.
    They tend now to be jammed full of electronics and anyone's guess as to what goes on in there but obviously some reason why it requires a specific level to initially turn on.
    Typical LED dimmer shown below.....
     

    Attached Files:

  11. dave9

    dave9

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    Mar 5, 2017
    ^ What indication do we have that it's a new style dimmer? I would have assumed an old triac design if already in use with incan bulbs.
     
  12. Bluejets

    Bluejets

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    I was going by the characteristic "new LED type dimmer" mode of operation which the OP supplied.
    I imagine we'll have to wait and see when they get back (if ever).
     
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