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Fluorescent Lights: Troubleshooting and other questions

Discussion in 'Electronic Basics' started by Uriah, Jun 9, 2006.

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  1. Uriah

    Uriah Guest

    Someone told me that if you leave a burned out fluorescent bulbs in
    their fixture with power applied you eventually damage the fixture.
    Then if you put a bulb in it will burn it out in a second.
    This seems to be true from my experience. Could someone explain why
    this happens and how do you test a fixture to see if it is OK before
    you place a new bulb in one and risk damaging the bulb.
    Thanks
     
  2. Phil Allison

    Phil Allison Guest

    ** A really desperate Groper.


    ** No such test is possible.

    If in doubt, replace the *starter* and use an old but functional tube to
    see if all is OK.

    Let it run for 24 hours before making any conclusions.




    ........ Phil
     
  3. Ballast damage is unlikely but I have known it to happen. Damaged
    ballasts usually make themselves known very quickly - usually by not
    working at all.

    More likely trouble from keeping a burned out fluorescent lamp operating
    is if there is also a starter - and that can wear out the starter.

    Bad bulbs are hard on starters and bad starters are hard on bulbs. But
    if you replace the bulb and only the ends glow due to a bad starter, the
    bulb suffers only minor to minimal damage if you pull either the bulb or
    the starter upon recognizing that this is happening.
    If the ends of the bulb glow *brightly* and the bulb does not start, it
    gets more urgent to pull at least one. Otherwise the ballast can
    overheat. Although UL testing supposedly means that the risk of a fire
    starting from this is negligible or "acceptably low", I know of one
    ballast that started a fire that way - in an elevator in an apartment
    building that I lived in before.

    If there are no starters and a replacement bulb does not start, check
    for:

    1. Fixture is properly grounded. This sometimes affects starting by
    affecting the electric field distribution within a bulb that is trying to
    start.

    2. The bulb ("lamp") is of a type that the ballast is rated for.

    3. Corroded connections, loose wires, etc.

    After that, in my experience most likely the ballast died. And in my
    experience, they die from at least mainly old age more than from
    attempting to run burned out bulbs. They are designed to not die from
    burnouts occurring when it will be many hours or days before maintenance
    workers do anything. Any ballast manufacturer designing a ballast likely
    to be used in commercial buildings I consider incompetent if the ballast
    is unable to survive working with a burned out bulb for months.

    - Don Klipstein ()
     
  4. Uriah

    Uriah Guest

    Thanks for the insights. I didn't realize that the glowing ends of the
    bulb, which I have seen many times, spelled failure. That will save me
    quite a bit in the coming years so I appreciate the info.

    Arcade games have a small fluorescent fixture in them and sometimes
    these games sit in locations for years with the bulb burned out. When
    I would go to replace the bulb the new one would just not start at all
    and then when I would try and place the same bulb in a new fixture it
    would also be dead. Can you measure the voltage on the fixture to
    check and see if it is within specs? What would you look for? Or can
    you with the power off check the ballast with the OHM settings on a DVM
    to see if there are shorts? And the same with the starter, is there a
    way to check it to see if it is the culprit? And... I am sorry about
    all of the questions but I have been meaning to fill in this missing
    knowlege for quite some time, how do you check a bulb to see if it is
    ok? Is putting it in a known working fixture the only way?

    I was working on a regular fluorescent fixture that lit a display
    counter in a store . When I placed a bulb in the fixture it lit up and
    I thought it was fine but it went out within a minute and when I
    touched the bulb it was really hot. There was no starter on this
    fixture. I don't know much about these things. What might have been
    happening with this one? And like in my above question can you check
    it with a DVM to see if it is OK before inserting the bulb? The bulb
    costs almost as much as the fixture.

    Thanks for the help I really appreciate it.

    Uriah
     
  5. Guest

    Yep - actually, theoretically a fluorescent tube doesn't have
    resistance (more than a piece of wire has), it just causes some voltage
    drop. So virtually, the ballast should survive from driving as shorted
    as well...

    For OP: It isn't virtually possible. Of course it is, but it's very
    unlikely - just like the Don said (ballast damage). When a tube is
    burned out, just replace it and try, if it starts, it's ok, if not,
    replace the starter, then it should be ok :)
     
  6. Makes me think the starter is stuck shorted and the ballast is shorted.

    Assuming that what you have is likewhat I had when I owned an arcade
    game...

    However, I would think that a fluorescent lamp burning out instantly
    from this would produce some sort of flash of light at the ends.
    If you have a 2-lead ballast, voltage will not tell the whole story. To
    check the condition of a ballast in a 14, 15, 20 or 22 watt 120V
    fluorescent fixture with a starter and a 2-lead ballast: Rig up a 120V
    40W or 60W incandescent lamp from one lead of one "lampholder" ("socket")
    to one lead of the other - using the leads other than the ones going to
    the starter.
    If the incandescent does not glow at all, you have an open ballast or a
    broken connection. If the incandescent glows at noticeably reduced
    brightness, then the ballast is almost certainly good. If the
    incandescent glows at full or nearly full brightness, then the ballast is
    shorted.
    Compare to a normal ballast of the same type and wattage. However, a
    short across part of a winding can make a minor decrease in DC resistance
    and a major decrease in impedance at 60 Hz.
    Starters should read open. But if it was used with a lamp that failed,
    then it should be replaced - especially if the lamp has failed beyond
    blinking or has spent a long time blinking.
    Most likely you used the wrong bulb for the ballast being used, such as
    a regular 40 watt 4-footer with a VHO, SHO or HO ballast.

    Second most likely is a failed ballast where the current limiting
    element is mainly a capacitor and the capacitor shorted. I saw one of
    those, but lamp life was shortened only to something like several hundred
    or about a thousand hours. Or you have a separate transformer and
    inductor with the inductor shorted - rare except in systems ported from
    one line voltage to another.

    - Don Klipstein ()
     
  7. Uriah

    Uriah Guest

    Don,

    Thanks for explaining all of that to me. I am going to print out and
    keep it in my Arcade Repair book as a reference for the future. I have
    always wondered about this things and now I finally know.

    Thanks
    Uriah
     
  8. Thanks!

    But I forgot something:

    When I said a good starter reads open on an ohmmeter, I did not mean
    that a starter that reads open is good. Only that one that does not read
    open (usually shorted) is definitely bad.
    This applies for the usual "glow switch" starters.

    - Don Klipstein ()
     
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