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Fluorescent Lamps

Discussion in 'General Electronics Discussion' started by alfa88, Feb 4, 2012.

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  1. alfa88

    alfa88

    332
    4
    Dec 1, 2010
    Back to basics. This is the way I thought they worked. The ballast provides a high voltage to get the mercury to ionize and then the voltage drops and the filaments on each side maintain the glow. However, my magnifying lamp wasn't working so I delved into what the problem might be. I made a schematic but now my concepts seem to be wrong. I'm confused.
    Turns out the tube wasn't getting properly seated.
     

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    Last edited: Feb 4, 2012
  2. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Yes, that's the way it works afaik too. A tube is made to operate on say around 170mA, and has a voltage drop according to length/wattage (some 40-70V).
    The ballast provides a filament current while the momentary is closed, an inductive kick when it's released, and a ~ constant current in normal operation.
    If one of the filaments are out you won't get preheating and hence no inductive kick either. Shorting the broken filament may enable re-lighting the tube.
     
  3. davenn

    davenn Moderator

    13,808
    1,943
    Sep 5, 2009
    i dont get it !

    If that circuit is correct, and that upper switch is truely momentary, ie. doesnt stay closed when the lower switch is closed, then there is gap in the circuit and no current can flow sustaining the light ??

    Dave
     
  4. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Yes, the lower switch is permanent and the upper momentary. The current flow is dependent on the ionized gas in the tube conducting from one end to the other.
     
  5. alfa88

    alfa88

    332
    4
    Dec 1, 2010
    Yea, that's what I was thinking. It's for sure a momentary pushbutton. When pushed you can see the filaments glow and when released the entire tube fires up so to speak.
     
  6. JMW

    JMW

    90
    3
    Jan 30, 2012
    The ballast limits the current flow when the lamp is operating. The vapor is highly conductive, the bulb would fracture if it wasn't there. A ballast is an inductor, it will maintain the voltage at a level to maintain ionization but limit the current to milliamps
     
  7. davenn

    davenn Moderator

    13,808
    1,943
    Sep 5, 2009
    Doh of course, what was I thinking ??!! just having a "blonde" moment

    apologies to all the blonds out there ;)

    Dave
     
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