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replacing UHP ballast with a coil one

P

Pawel Paron

Jan 1, 1970
0
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
 
P

Pawel Paron

Jan 1, 1970
0
Dnia 20.02.2007 JB said:
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.

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
 
J

JB

Jan 1, 1970
0
Pawel Paron said:
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.
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
 
P

Pawel Paron

Jan 1, 1970
0
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
 
D

Don Klipstein

Jan 1, 1970
0
Pawel said:
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).

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 ([email protected])
 
V

Victor Roberts

Jan 1, 1970
0
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

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
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site without written permission.
 
D

Don Klipstein

Jan 1, 1970
0
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.

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 ([email protected])
 
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