Switching 12V Halogen bulbs

Discussion in 'The Projects Forum' started by russpatterson, May 29, 2011.

  1. russpatterson

    Thread Starter Member

    Feb 1, 2010
    351
    16
    So I need to run some current through my circuit to test. I don't have the actual load yet (strings of 12V LED's) but I need to draw 3.3 Amps through the power stuff in my circuit to see if I've got any thermal issues or anything. I picked up some 35W 12V Halogen bulbs at the hardware store. Any problem with switching them at 200 - 5K Hz?

    I think they would just dim but maybe this is something that everyone knows but me. Like they can be dangerous when you switch them at high frequency.

    Thanks!
     
  2. #12

    Expert

    Nov 30, 2010
    16,313
    6,818
    The halogen bulbs that I know about simply use an inert gas (a halogen) as the atmosphere in an incandescent bulb. It suppresses outgassing from the filament (which darkens the glass bulb) and conducts heat away from the filament to allow for a hotter incandescence (whiter light) without burning the filament in half. Bottom line? It's just a light bulb.

    Other people might know about different definitions of "halogen bulb" and provide some more useful information.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The halogen is iodine. It combines with the deposited tungsten on the glass envelope and will deposit the tungsten back on the hot filament.

    Given that tungsten loads vary so much cold to hot, a fixed resistance would probably be better as a test load.
     
  4. #12

    Expert

    Nov 30, 2010
    16,313
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    Too cool! Iodine acting as millions of miniature taxi cabs delivering tungsten back to the filament!

    ps, good point about the cold start resistance of tungsten filaments.
     
  5. russpatterson

    Thread Starter Member

    Feb 1, 2010
    351
    16
    So no danger just not the greatest test load?

    Agreed, I need to make an adjustable constant current load. For now I'll try these out. Thanks!
     
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,792
    948
    If you have any old toasters laying around... the element in them will form an excellent resistor. If it is a 120VAC unit, then something between 1/5 and 1/10 of its length should be about right. Experimentation will be needed...I love experimentation. Even the sound of the word is nice. :)
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,140
    3,054
    I think there IS a mild danger to your circuit, if the peak amps to a cold filament (when resistance is lowest) is more than your circuit can take for that instant. Once the filament has warmed, everything should be fine. It will "coast" between AC peaks and maintain most of its temperature. 60 Hz is no problem, so your higher frequencies will be fine. It's just that first millisec or so. Your circuit may have no problem at all with that, but it's an issue to consider.
     
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