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Halogen bulbs

Discussion in 'Hobby Electronics' started by Mainlander, Jan 14, 2004.

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  1. Mainlander

    Mainlander Guest

    As noted in my post in I am having difficulty sourcing an H3 6V
    15W bulb for a cordless rechargeable spotlight. I have since discovered
    this type is virtually unobtainable in Australasia.

    Calculations based on a 12V 55W bulb drawing approx 4.6 A @ full power
    suggests when operated on 6V the current should be halved to 2.3A, this
    gives a power of 14W which is acceptably close to the output of the
    original bulb. However this assumes the lamp is as efficient at the lower
    voltage as at full voltage, can halogens be "dimmed" or operated at lower
    voltage with the same efficiency?

    It appears the problem in this particular spotlight light is not the
    bulb, but a break in the track of the small internal PCB, however in the
    course of attempting to find a replacement the bulb has been handled so
    much that its life will be shortened in any case.

    The advantage is that 12V 55W is a very commonly available size for the
    H3 bulb that is commonly used in automotive applications and these
    rechargeable handheld spotlights. Most such lights have a rating of 30 -
    55W with correspondingly shorter battery life.
  2. The place you bought the lamp from will be able to help, if not then they are
    not providing spares for the product they sell, so you can get it resolved under
    the consumer guarenties act, possible a new light or similar.
  3. I've found it difficult to obtain just about any higher power 6v halogen. I
    was trying to get more lighting power for my bicycle lights, and gave up
    looking for spares and higher powers. I went to 12v halogens. Disregarding
    the mounting issues, they are a LOT cheaper and a LOT easier to obtain.
    You can't do that with halogens (or normal incandescents for that matter),
    reducing the voltage will greatly reduce their output, because of that, reduce
    their temperature, and because of that, reduce the filament regeneration cycle.
    Lastly, it's the halogen filament regeneration that gives them their long life.
    The exception is normal incandescents, which benefit from a longer life if
    you run them at lower than rated voltage.

    Also, operating an incancescent or halogen lamp at lower than their rated
    voltage tends to shift the output closer to infrared, so you get more heat and
    less light for your watts. (less efficient). Anectodal evidence (well, google)
    says dimming a 500W mains operated halogen to 300W will give you equivalent
    light output as a 40W bulb. You get the idea, dimming battery operated lights
    is generally not a good idea if you're looking at improving battery life.
    Can't you repair this break? I don't think it's rocket science...

    On the note of halogen handling, if you haven't powered it up since touching
    it, cleaning it with alcohol then water will remove the oils from the surface
    (which cause the trouble).
    Not if you can't supply 12v to operate them. (Or can you?)
  4. Mainlander

    Mainlander Guest

    I want to keep this one if possible because it has a much more useful 90
    minute battery life than most of the bigger ones which run for only 30
    minutes, thus I would rather have a bulb for it than replace it with a
    bigger one.
  5. Mainlander

    Mainlander Guest

    The 6V 30W and 55W sizes are relatively easy to obtain in Australia and
    250 hours is a "long life"? That is the rated life of most of these
    bulbs, I would not call that long.
    Even if I could supply 12V I couldn't get a 15W one, because if the
    fitting is designed for 15W higher power lamps are likely to cause damage
    from the extra heat.
  6. Unfortunately, because most bulbs have a positive temperature
    coefficient of resistance and the filiament undergoes a marked change
    in temperature, the current drawn at half voltage will be much less
    than half that drawn at full voltage.

    You may find that you get far less than 14W from that bulb -- in fact
    it might glow a rather dull red rather than white. What's worse, if
    it's a hallogen then the hailides inside will not operate as designed
    at these lower temperatures so the bulb life may be affected.
  7. Brummer

    Brummer Guest

    Jaycar sell 55W, 25W and 10W in 6V versions, specifically for torches and
  8. Phil Allison

    Phil Allison Guest

    "Bruce Simpson" <

    ** A filament bulb tends towards a constant current characteristic -
    i.e. the current does NOT change in proportion to the applied voltage. At
    half the nominal voltage the current will be around 75%.

    As you said, there is a strong positive temperature coefficient in the
    tungsten wire - about *12 times* increase in resistance from cold to hot.

    .............. Phil
  9. Ah, ok, but you say you'd rather not use these due to the lesser battery
    life... They're probably too bright anyway.
    250 hours!? Stuff that for a joke. I'm using standard 35mm, 7degree 12W 12V
    downlights on the bicycle. 2000 hours life. I break them before I run out of
    life. And at less that AU$20 a pop, who cares?

    Retrofitting one into a largish frame torch might need a bit of imagination
    and perhaps lateral thinking, but certainly doable.

    If you don't care about how it looks, you could bodgy up a plain 6v lantern
    battery type torch, even fan force it if you need to, and replace the 6v
    lantern style battery with a 4A/Hr SLA battery. Would probably still end up
    being cheaper than the fancy 6v torches.
    True. I was in a similar boat with my bike lights. I had spent stupid
    amounts of money on them, and they were all not quite bright enough, or didn't
    have enough light spread.
    In the end I wrote off the money I had already spent as a lesson learned and
    went the downlight route.
    Cheap, simple, and does the job.
  10. Phil Allison

    Phil Allison Guest

    "John Tserkezis"

    ** The life of a lamp is a function of brightness and efficiency - the
    more the less.

    2000 hr rated life lamps are dull, yellowish and inefficient - for AC
    mains operation no problem.

    50 hr rated life ones (as used in 35mm slide projectors) are brilliant
    white and have way more lumens per watt - essential for good colour temp
    and image quality.

    Torch bulbs typically have short lives - maybe only 10- 20 hours at full
    voltage - for a reason.

    ........... Phil
  11. Mainlander

    Mainlander Guest

    Can't use a 30W bulb in a fitting designed for 15W bulbs.
  12. Mainlander

    Mainlander Guest

    The H3 / H4 bulbs are automotive types typically quoted 250 hours by
  13. Phil Allison

    Phil Allison Guest

    ** And your point is ??????

    ............. Phil
  14. Actually, the current will be significantly more than half that drawn at full voltage.

    True, it's not going to operate very well at half voltage. The spectral
    density will be way off and lifetime could be terrible due to due to deposits
    on the envelope.
  15. larry

    larry Guest


    thanks for the info.
    I never knew this before
    it explains a lot

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