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Re: Pulse Start MH Ballast

Discussion in 'Lighting' started by Victor Roberts, Mar 10, 2006.

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  1. Philips has a warning in their print catalogs that standard
    or protected metal halide lamps should not be used in pulse
    start fixtures or with pulse start ballasts. They state
    doing so will increase the risk of outer bulb rupture.

    It is not clear to me why there is an added risk, since both
    probe-start and pulse-start 400-watt metal halide lamps are
    rated for an operating current of 3.2 amps. There may be a
    difference in the starting current, but that will take more
    time to investigate.

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
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  2. Before I "specialized" in fluorescent lamps, 41/2 years ago, I was a
    Commercial Engineer for OSRAM SYLVANIA and had responsibility for
    specifier contacts with field technical information for all lamp types.

    Two things about the porbe start lamp design. #1 Their main mechanism
    of failure is to fail to start. Hit them with the starting circuit of a
    pulse start ballast and they may never fail to start which means they
    will continue to operate (at high internal pressures and temperatures
    inside the capsule)as they grow gradually weaker and weaker in physical
    strength, operating beyond expected life. This can lead to an increased
    probability of violent failure of the capsule as the lamp is operating
    under conditions it never would have reached if properly ballasted. #2
    Lead wire positioning and insulation inside the base of the lamp for a
    probe start lamp is based on the open circuit voltage of the M57 (for a
    400W) ballast. Granted, there are safety factors built in, but a pulse
    start ballast's ignitor circuit provides signifiacntly higher voltage to
    get the (differently designed)pulse start lamp to start. There used to
    be a hihgher probablility of arcing inside the base if a probe start
    lamp were operated on a pulse start circuit. (Note: this may have
    changed in the past 5 years, I don't know)

    The advantages of higher lumen maintenance for the pulse start lamp was
    because the lamp was designed with higher internal capsule fill pressure
    when the lamp is not energized. This reduces the "sputtering" losses
    from the electrode during startup, but it dramatically increases the
    starting voltage required to initiate an arc. Pulse start lamps willnot
    strat reliably, if at all, on probe start ballasts. The only effect of
    the Super CWA (M135) ballast is to provide the higher starting pulse
    required to get the thing started. Once it does strike, as has been
    noted, the Short Circuit Currrents and operating current ranges ar the same.

    Jeff Waymouth
     
  3. Why do you think the ballast design creates the advantage?
    Pulse start lamps have at least two advantages, both in the
    lamp. The absence of the starting probe allows the ends to
    be made smaller, which makes the arc tubes more isothermal.
    This allows for higher cold spot temperatures which produces
    higher efficacy, while not overheating the center of the arc
    tube. Also, the start is cleaner which leads to less
    electrode sputtering and therefore better lumen maintenance.
    And, as Jeff has pointed out, the fill pressure is higher,
    which also leads to better lumen maintenance.
    Mostly the probe requires a large end seal which is then
    colder than is desired.
    I see that you cut that part of my original message that
    stated that Philips says probe-start MH lamps operated on
    pulse-start ballast have a greater risk of exploding. That
    is far worse than short lamp life. It is safety issue that
    should be taken seriously.

    --
    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.
     
  4. CMH lamps, like HPS lamps do not have room for a starting
    probe in the ceramic end cap - so they are all pulse start -
    just like HPS lamps.

    --
    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.
     
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