Metal Halides Lamps Failing Prematurely

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MBack

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I've got a situation that has me stumped.

I've got 70 enclosed, pendant mounted fixtures installed in a library. Each has a 175W metal halide lamp. The ballasts are F-can type and are remotely mounted in a closet approximately 200 feet away.

After initial install (renovation project), the lamps started failing (severe color shift and decreased light output) after about 4000-4500 hours. They were all relamped. Same thing is now happening again after 3500-4000 hours of operation. The average lamp life is rated 10,000 and they are installed in the proper burning position.

The lamps operate 6 days a week, 12 hours a day continuous.

Two things I noticed that may be problems with the installation are:
1) The ballasts were mounted directly on a plywood backboard in rows with minimal separation between ballasts. (Heat issues?)

2) The wire gage from the ballast to the fixture is less than what the ballast manufacturer called for. (Voltage drop?)

I sent a couple of ballasts to the ballast manufacturer for testing and they showed no signs of heat problems.

I sent the lamps to the lamp manufacturer and there were no obvious problems with the lamps.

Neither the lamp manufacturer nor the ballast manufacturer could pinpoint the problem.

Anyone have an idea what could be causing the problem?
 
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Mr. Bill

Mr. Bill

Senior Member
Location
Michigan
My guess is the wire size. I designed a project similar to this but the HID lamps were pulse start. I didn't realize that pulse start ballasts have issues with remote mounting. The ballasts kept burning up even before the building was turned over to the Owner. I found a chart somewhere for upsizing wiring for remote mounted pulse start HID. After new, larger wire was installed I haven't heard of any problems since.
 
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Lcdrwalker

Senior Member
Location
Columbus, Ohio
Try checking for proper voltage and voltage drop. I believe that the 175 MH ballast should have an output of around 330 volts. It should be labled on the ballast.
 
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Psychojohn

Member
Location
Oshkosh, Wisconsin
The way I read it, these are turned off and on every day.
These are the same lamps we use, other than the ballasts are at the fixture.
We relamp about once a year (8760 hours) and never have to replace a bad one, untill we cycle them.
Then we end up changing a few that will not relight.
I don't know if that is what is reducing your bulb life, but you might want to ask the manufacturer.
 
M

MBack

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Not sure why the contractor installed smaller gage wire than what the ballast manufacturer called for. I was not involved with the project then.

The ballasts are the original ones. They have not changed. The open circuit voltage at the fixture was measured to be about 305 volts which is what is expected. But with no load, you wouldn't see a voltage drop.

We're going to have the site electrician measure the short circuit current and see if that is within the ballast manufacturer specifications.
 
M

MBack

Member
Well, the short circuit tests (with a true-RMS meter) showed readings of 0.2 to 0.4 amps at the lamp socket (lamp removed). The ballast spec indicates these readings should be 1.5 to 1.85 amps.

Does this confirm a voltage drop problem?
 
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