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Will a 1500 watt MH ballast work with a smaller bulb?

M

Michael Shaffer

Jan 1, 1970
0
I'm guessing this won't work, but could i use a 150 watt metal halide
bulb with a 1500 watt multi-tap ballast?
 
J

JB

Jan 1, 1970
0
Michael Shaffer said:
I'm guessing this won't work, but could i use a 150 watt metal halide bulb
with a 1500 watt multi-tap ballast?

Only if you don't mind sweeping up the fragments of the 150W lamp.

JB
 
J

JohnR66

Jan 1, 1970
0
Michael Shaffer said:
I'm guessing this won't work, but could i use a 150 watt metal halide bulb
with a 1500 watt multi-tap ballast?

Besides providing the voltage necessary to start the bulb, a ballast is a
constant current source for the lamp. a 1500w ballast will provide
considerable more current than the 150w lamp needs. Consider the nature of
an arc. It will conduct and get hotter and will conduct more (negative
resistance effect). The 150w bulb will handle the current from the 1500w
ballast for a short time. I'd expect one of the following possibilities:
1. The bulb will explode
2. Something will burn up
3. Something will burn down

John
 
V

Victor Roberts

Jan 1, 1970
0
I'm guessing this won't work, but could i use a 150 watt metal halide
bulb with a 1500 watt multi-tap ballast?

Unless the taps are designed specifically to operate the 150-watt lamp
you have the lamp *will* BLOW UP and possibly start a fire or injure
someone.

--
Vic Roberts
http://www.RobertsResearchInc.com
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D

Don Klipstein

Jan 1, 1970
0
Only if you don't mind sweeping up the fragments of the 150W lamp.

Or removing them from people that the fragments shot into...

Or putting out any fires that got started by red-hot or hotter
fragments...

Then again, most metal halide lamps are supposed to be operated in
suitable enclosures because every few blue moons one explodes somewhere
even when used as directed, although usually but not necessarily after:

1. a change in brightness/color that is obviously degradation if someone
is paying attention, or

2. the lamp has been run past its life expectancy, or

3. the lamp has experienced a degradation that impairs it restarting after
being shut off. I have heard of a recommendation to occaisionally
shut down HID lamps that otherwise would operate 24/7 and replace ones
that fail to restart.

As for operating an HID lamp with a ballast not specifically rated as
compatible with it, this is something experimental. Mismatches in wattage
in either direction tend to reduce lamp life, and metal halides can go out
with a bang. Overwattage easily causes a metal halide lamp to explode,
and fragments of an arc tube will be hot. I believe a typical arc tube
operating temperature in a metal halide lamp is normally around 800 C,
or about 1500 degrees F, and fixtures for metal halides (other than
"protected" types) are supposed to withstand arc tube fragments at 1000 C,
slightly over 1800 F. Even higher temperatures are likely if the lamp
explodes from overwattage - although short of the melting point of quartz,
roughly 1700 C or roughly 3100 F, which is roughly the temperature of a
typical Bunsen burner or propane torch flame.

"Protected" type metal halide lamps can be used in open enclosures but
only if the lamp is used as directed with a rated-as-compatible ballast
being used as directed.

----------------------------

As for a 150 watt lamp on a 1500 watt ballast - I expect the lamp to
fail somewhere between several seconds and a few minutes after starting.
The lamp may even have portions of its electrodes melt in anywhere from a
fraction of a second to a few seconds, which can make it not run properly
when used as directed (and make its arc tube ends run hotter than normal
if it is able to run when used as directed). Metal halide lamps operated
at severe overwattage may become more dangerous than usual to use even as
directed as a result of highly severely abusive overwattage/overcurrent
that is discontinued before the lamp completely fails.

----------------------------

If you have lamp wattage and ballast wattage mismatched, what usually
happens is that the wattage delivered to the lamp is closer to that which
the ballast was designed for than that which the lamp was designed for.

- Don Klipstein ([email protected])
 
T

TKM

Jan 1, 1970
0
Don Klipstein said:
Or removing them from people that the fragments shot into...

Or putting out any fires that got started by red-hot or hotter
fragments...

Then again, most metal halide lamps are supposed to be operated in
suitable enclosures because every few blue moons one explodes somewhere
even when used as directed, although usually but not necessarily after:

1. a change in brightness/color that is obviously degradation if someone
is paying attention, or

2. the lamp has been run past its life expectancy, or

3. the lamp has experienced a degradation that impairs it restarting after
being shut off. I have heard of a recommendation to occaisionally
shut down HID lamps that otherwise would operate 24/7 and replace ones
that fail to restart.

As for operating an HID lamp with a ballast not specifically rated as
compatible with it, this is something experimental. Mismatches in wattage
in either direction tend to reduce lamp life, and metal halides can go out
with a bang. Overwattage easily causes a metal halide lamp to explode,
and fragments of an arc tube will be hot. I believe a typical arc tube
operating temperature in a metal halide lamp is normally around 800 C,
or about 1500 degrees F, and fixtures for metal halides (other than
"protected" types) are supposed to withstand arc tube fragments at 1000 C,
slightly over 1800 F. Even higher temperatures are likely if the lamp
explodes from overwattage - although short of the melting point of quartz,
roughly 1700 C or roughly 3100 F, which is roughly the temperature of a
typical Bunsen burner or propane torch flame.

"Protected" type metal halide lamps can be used in open enclosures but
only if the lamp is used as directed with a rated-as-compatible ballast
being used as directed.

----------------------------

As for a 150 watt lamp on a 1500 watt ballast - I expect the lamp to
fail somewhere between several seconds and a few minutes after starting.
The lamp may even have portions of its electrodes melt in anywhere from a
fraction of a second to a few seconds, which can make it not run properly
when used as directed (and make its arc tube ends run hotter than normal
if it is able to run when used as directed). Metal halide lamps operated
at severe overwattage may become more dangerous than usual to use even as
directed as a result of highly severely abusive overwattage/overcurrent
that is discontinued before the lamp completely fails.

----------------------------

If you have lamp wattage and ballast wattage mismatched, what usually
happens is that the wattage delivered to the lamp is closer to that which
the ballast was designed for than that which the lamp was designed for.

- Don Klipstein ([email protected])

Oddly enough, the "birth" of the 1500 watt metal halide lamp ocurred when a
lighting fixture company -- then in Chicago -- desperately needed more light
per fixture for a sports lighting project and so designed a ballast that
operated standard1000 watt metal halide lamps at 1500 watts. Lamp life of a
few hundred hours was acceptable, so the fixture company proceeded to test
the system. Light output and color were both surprisingly good and the
system was installed. Later, lamp companies changed the lamp designs to
increase lamp life and such lamps are in widespread use today.

Normally, of course, overdriving an HID lamp results in problems such as you
have described, Don, and it is definitely not recommended for safety reasons
alone.

Terry McGowan
 
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