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replacing UHP ballast with a coil one

Discussion in 'Lighting' started by Pawel Paron, Feb 20, 2007.

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  1. Pawel Paron

    Pawel Paron Guest

    Hi,

    I'm investigating options to replace a damaged ballast in an LCD projector.
    There is a 120W UHP bulb in this projector, as I found its operating voltage
    is about 75V (some source claims 65V). I would like to connect an external
    MH coil ballast and ignitor, but I'm confused what the rated power of this
    ballast should be. I don't remember exact numbers, but seems, that a general
    purpose MH lamps in the range of 75-150W have somewhat higher operating
    voltages, 90-100V or so. Considering that, what would be a general rule,
    should I look for a higher or lower rated MH coil ballast, or as close as
    possible to the original 120W? There isn't much choice, like 75W, 100W and
    150W, which one would fit best? I would prefer to underpower than overpower
    that UHP bulb.

    Thanks in advance for any help

    Pawel
     
  2. Pawel Paron

    Pawel Paron Guest

    OK, I understand your warning. But assuming that I insist to try, and
    considering only the power issue, what magnetic MH ballast should I look
    for, to run this UHP lamp at about its rated power, that is 120W? A standard
    150W MH ballast runs a standard MH 150W bulb at about 100V, which means
    1.5A. When I wire it up to this UHP bulb, which operates at 75V (and
    requires 1.6A when running at rated power), what would be the expected power
    of the lamp? Higher or lower than 120W? Or I should try a 100W MH ballast?
    Or maybe a 75W one? Or two 250W, wired in series?

    Regarding the ignitor, I also worry it might be a problem to strike the lamp
    with a conventional MH ignitor, but on the other hand, I checked specs for
    similar UHP bulbs, and the ignition voltage is specified as about 5000V,
    which is within the range of a standard MH ignitor (at least the ones I have
    handy in my drawer).

    Pawel
     
  3. JB

    JB Guest

    One word: Don't! These lamps will *only* operate on the electronic ballast
    designed specifically for the purpose. No conventional electromagnetic
    ballast can possibly provide the correct running characteristics for this
    type of lamp. Even if you do get the lamp to strike (and without a special
    ignitor you won't in any case), the lamp will not be stable, will not run at
    the correct power level and may even explode.

    JB
     
  4. Pawel Paron

    Pawel Paron Guest

    So here is a quick experiment I just made, using parts I had handy: coil
    ballast for a 150W MH bulb, standard parallel ignitor for a 50-1000W metal
    halide bulb (parallel means two terminal wires, not three), some unknown
    160W UHP projector lamp. There was absolutely no trouble starting the lamp,
    it surely ignites with no blinking and no other symptomps of startup
    problems.

    But I measured voltage across the lamp and it was apparently too low, just
    about 28V, so I assume that current was probably too high, and I disconected
    it quickly, without waiting till this lamp fully warms up (or maybe
    explodes). And I still have no idea what "general purpose" coil ballast
    would be best for a 120W UHP lamp.

    Regards
    Pawe
     
  5. The voltage will be low until the lamp is warmed up, or at least the
    mercury is all evaporated.

    WARNING - the voltage may or may not reach a normal voltage when a lamp
    is warmed up with excessive current. Also, excessive current as well as
    excessive power may damage the lamp - excessive current can cause damage
    even when power is not above rated (from voltage being low due to lamp
    being not yet warmed up).
    WARNING - I don't know if any of these lamps have a current crest factor
    requirement that magnetic ballasts cannot meet. Excessive current crest
    factor can cause lamps to age at an excessive rate. The lamp could
    possibly experience discoloration and then overheat and then possibly
    overheat in a non-passive manner.

    - Don Klipstein ()
     
  6. These lamps run at a pressure of 200 atmospheres and with
    molten electrode tips. Do you really want to experiment
    with non-standard ballasts for a lamp that operates at such
    a high pressure?

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  7. I meant to say at the end "fail in a non-passive manner". As in BANG
    with shrapnel including pieces of bulb material at temperature maybe
    900-100 degrees C. Experiment at your own risk, preferably with lamps in
    suitable containers!

    - Don Klipstein ()
     
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