Battery/line powered ballast

Discussion in 'General Electronics Chat' started by inwo, Feb 11, 2014.

  1. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Ran across a couple fluorescent ballasts today.

    They supposedly can run a lamp for an hour and a half on internal battery power.

    Or work on AC.

    They don't seem to be potted.
    Outdated but new. Have to assume the batteries are bad. Unless they are nicad. I think they can stand long discharged times better.

    What would be a good project for them?
    Other than intended use, which wouldn't be too bad either.

    Must be 1500 volt inverter or what ever the lamp needs.
    Mini Tesla coil? :eek:

    I'm sure I could get them for any reasonable offer.
     
  2. #12

    Expert

    Nov 30, 2010
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    What purpose? Haven't a clue.
    However, an inductor and a switch can make a firing voltage pretty easily. From 1/2 LI^2 = 1/2 CV^2 you only need the capacitance of the bulb to calculate an inductor that will create a kilovolt or more to do the first ionization pulse.

    Say, the bulb has 2000 pf and needs 1500 volts to arc over.
    1/2 2000 pf 1500^2 = 1/2 L I^2
    LI^2 = .0045
    A hundred millihenries would need .212 amps suddenly switched off to make a 1500 volt kick. Still, most manufacturers use a pulse transformer to get the starting kick. That lowers the voltage rating on the transistor quite a lot.

    Get the drift?
    Or did I just wander off on an idea that has no use for you?
     
  3. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    Ok, I get it.:p
    It may not be that high a voltage.

    I thought the electronic ballasts were just high voltage inverters. I'm sure there's a lot more to it.

    I'll try a search to see what the running voltage and current of a T8 bulb is.
     
  4. #12

    Expert

    Nov 30, 2010
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    I draw my experience from some High Pressure Sodium lamps I use for outdoor lighting. They are nothing more than an inductor which limits current as Xl = 2 Pi F L
    and an, "igniter". The igniter is used to make a pulse every few seconds. After the arc is struck, the inductor provides voltage, "as much as necessary" to keep the lamp on. The fast igniter pulse is protected from escaping into the power lines by the inductor that limits the current.
     
  5. inwo

    Thread Starter Well-Known Member

    Nov 7, 2013
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    These must be inverters as they are battery powered.

    I think I'll pick one up and dissect it.
     
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