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Dimming 50W G5.3 Halogen Desk Lamp? How?

Discussion in 'Electronic Design' started by Sizz, Mar 26, 2007.

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  1. Sizz

    Sizz Guest

    Hi, I am currently building a desk lamp which requires some form of
    dimming.
    Specifications:
    1x 12Volt Transformer (Suitable for dimming)
    1x 50watt G5.3 Bulb

    How can i create a dimming device which allows the user to dim the
    halogen bulb which is suitable for them? Using a potentiometer? What
    kind?

    Any information regarding circuits/diagrams/material would be much
    appreciated?

    Thanks
     
  2. You can buy a transformer style dimmer off the shelf. They are designed to
    provide symmetry.
     
  3. Rich Grise

    Rich Grise Guest

    I've heard it said that you shouldn't even try to dim a halogen bulb -
    if it runs below operating temp, the filament vapor will condense on
    the bulb envelope; I guess if you want to _permanently_ dim it, that'd
    be OK.

    Why not just replace the bulb with one that's not so bright?

    You could also get some neutral-density filter plastic, but you have
    to watch out for waste heat.

    Good Luck!
    Rich
     
  4. Sizz

    Sizz Guest

    Hey Rich,

    The only reason for dimming the halogen bulb is because different
    people want different brightness levels whilst working. This lamp
    would be for anyone as you are able to dim it to suit your needs.

    Ive looked at several articles and i have mixed feelings about this
    topic. Some people say it is possible and others say it isnt.

    I need a simple solution which can be incorporated into a desk lamp (a
    small unit)

    Thanks
     
  5. Ukaniu

    Ukaniu Guest

    look at graph showing lifetime of standard car halogen lightbulb. I think
    there will be no problem with shortage of life with decreaseing voltage.
    Especially when you do not dimm it more than 20-30%.

    Lukasz
    Cheers from Poland
     
  6. Phil Allison

    Phil Allison Guest

    ** Groper Alert !


    ** A 240 volt, triac dimmer intended for transformer fed loads is what you
    need.

    On sale at any lighting supplier.

    Millions in use - no problems with halogen bulbs.


    ** Best avoid any schematics that use a diac or neon bulb.

    Such circuits do NOT work correctly with transformer fed lamps.

    Schems using an opto isolator to drive the triac (eg the MOC3021) are likely
    OK



    ......... Phil
     
  7. I don't know about that. My wife has two of these fire hazards. One has a
    continuously variable dimmer knob, but the pot seems to have died in it.
    The other has a three position switch allowing for two brightness levels.

    I once heard something like you describe though, but IIRC they also said
    that running it at full voltage again would restore the bulb. Anyone?
     
  8. John B

    John B Guest

    On 27/03/2007 Anthony Fremont wrote:

    ..
    ..
    ..
    Running the lamp at full temperature may restore a blackened lamp, but
    there's no guarantee. It's called the 'Tungsten Halogen Cycle' and
    there's a neat animation here:

    http://www.donsbulbs.com/cgi-bin/r/d.pl/tungsten_halogen_cycle.html
     
  9. I used a lot of these types of bulbs back in my college theatre days.
    They work just find dimmed (all we ever did with them in the theatre)
    but are best if they at least occasionally brought up to full brightness
    and temperature.

    Charlie
     
  10. Sizz

    Sizz Guest

    Yes, i've found these comments useful. Some people say it can be
    dimmed, others say it shouldnt be dimmed.
    Do i just use a potentiometer and connect it to the 12v supply?
    Is there another way of dimming the halogen bulb using a potentiometer
    and a resistor of some sort? What kind?
     
  11. Phil Allison

    Phil Allison Guest

    "Sizz"

    ** Piisssssss Head.


    ** Hey, FUCKWIT !!

    Go look up TRIAC DIMMER on Google.

    And dam well read what is in replies even it is it NOT what you, in your
    infinite ignorance, wanted to see.




    ....... Phil
     
  12. There is no definitive answer to this.

    I remember looking at some book in a university library over 20 years
    ago, showing lots of graphs and equations expalining what supposedly
    happens to the halogen cycle when a halogen lamp is dimmed.

    Supposedly, dimming a halogen lamp slows down tungsten evaporation
    more than it slows down the halogen's returning of tungsten to the
    filament.

    Now, for a couple things going wrong:

    1) Dimming a halogen lamp is likely to not extend its life as much as
    dimming a non-halogen one does. The ends of the filament are cooler, and
    can be attacked by the halogen cycle, causing thin spots in the filament.
    These "end notching" sites can have temperature overshoot during a cold
    start. Soft starting can help here (and usually helps less with
    non-halogen lamps, where most fatal filament thin spots usually have
    excessive temperature in steady operation, and worsen at a rate
    accelerating worse than exponentially).
    Such filament end notches will worsen until failure occurs there one way
    or another.
    The bottom line is not dimming shortening life, but dimming extending
    halogen lamp life less than it does with non-halogen lamps.

    2) Halogen lamps could contain contaminants that do the halogen cycle in
    reverse - transporting tungsten from the filament to the inner surface of
    the bulb. Such bad stuff may slow down less from dimming than the proper
    halogen cycle does. In such a case, dimming to the extent where a
    contaminant's "reverse halogen cycle" outruns the normal one will cause
    problems.

    I suspect such problems are less with halogen lamps made by major brands
    such as GE, Osram/Sylvania, Philips, Thorn and Ushio. I suspect that such
    lamps will take mild to moderate dimming well and *usually* (maybe or
    maybe not reliably) not blacken with severe dimming. No guarantee from me!

    Now, for fixing blackened halogen lamps:

    I hear that this works. I suspect it works only if the blackening is
    simply tungsten, as opposed to an oxide (dusty grayish or colored). I
    would also be a bit leery of doing this, since with full power operation
    before the blackening is fixed the bulb can overheat. Every blue moon or
    something like that, a halogen lamp somewhere explodes even if nothing
    wrong is done, so I am leery of doing anything that increases stress on
    them.

    - Don Klipstein ()
     
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