Film-Tech Forum ARCHIVE: Bad Lamps and Power Readings

This is topic Bad Lamps and Power Readings in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by James R. Hammonds, Jr (Member # 673) on 02-18-2003, 11:15 PM:

In this particular house, we run 6000 watt OSRAM XBO lamps in a Strong Hilight II lamphouse with a FXPS type High Reactance power supply.

Upon starting the first show today, the picture was really dim and you could see that the bulb had darkened quite a bit.
At some parst you could barely even tell there was a picture on screen.
I took an amperage reading with a clamp meter and it read 192 amps when the maximum for that lamp should be 165.
The tap settings on the power supply were where they should have been and the tech said that the lamp most likely blew a seal and just needed to be replaced and sent in for warranty (300 hrs old).

We put the new lamp in and wre able to get a nice bright picture.
With the tap settings remaining the same, we now have an amp reading of 160.

The question I have is did the amp reading when the bad lamp was in place read so high because it was trying too hard to power the lamp or could there have been something wrong that was making the power supply put out too much power and damage the lamp?

Posted by Tim Sherman (Member # 569) on 02-19-2003, 08:08 PM:

I had just about the same problem this past summer you are talking about with a 4,200 watt superior quarts. It was a brand new bulb and was only on its second day of use and the amperage all of a sudden jumped from about 140 to 195. No matter how much i lowered the taps i still couldn't get the amperage down where is should have been. When i changed the bulb back to the old one the problem was gone. I was very suprised the breakers didn't trip during the show. You couldn't touch them thats for sure. 30 amp breaker with 33amps running through it can get pretty hot, and even discolor the breaker.

Posted by Pat Moore (Member # 380) on 02-19-2003, 08:29 PM:

A High Reactance power supply simply provides power to the lamp, essentially on demand. It is a "constant power" device, in that the wattage it puts out remains constant -- the lamp itself determines the amperage and voltage that use up that power. When you got the 190A reading, did you get a voltage reading as well?

I would imagine this lamp has a seal leak or some other problem, although that usually gives a very high voltage reading and a lower current reading. I think it just lived out its life.

Pat

Posted by Michael Schaffer (Member # 1204) on 02-20-2003, 03:42 AM:

If the lamp is leaking, it should turn black and blue and white like a twisted candy stick.
If the lamp is darkened after only 300 hours it suggests that the arc is wandering and the electrodes have degenerated. That would also explain the high ampère reading.
As I wrote before, check the stabilising magnet!!!!!
Or the lamp is not fitted into its holder properly and therfeore draws too much current.

Posted by Stephen Furley (Member # 1277) on 02-20-2003, 05:38 AM:

Tim wrote:

quote:

30 amp breaker with 33amps running through it can get pretty hot, and even discolor the breaker.

This doesn't sound right. A breaker passing 10% over its rated current shouldn't be getting hot, and most need more than a 10% overload to trip. If a breaker is getting as hot as you say it is then there is something wrong, either it is passing much more current than you think it is, in which case it should have tripped, or the contacts are poor, dirty, pitted, etc., and there is a high resistance there. Another possibility is bad connections between the breaker and its cables. Apart from any other problems you may have, I think you need to overhaul, or replace this breaker, it sounds like a safety hazard in its present condition.

Posted by James R. Hammonds, Jr (Member # 673) on 02-20-2003, 11:47 AM:

Pat, I did not take a voltage reading because we take all of our readings either with a clamp meter or with volt meter using leads.
We could not do this while the show was running, and by the time the show finished, it was determined that the seal had probably broken and that we were just going to change the bulb after the show.
We do not use the digital display board for the power eradings because they are unreliable.
Clamp meter will tell us one thing.
Display board will tell us another.
Plus the displays like to go out more often than we would like them to.
The lamp was only 300 hours old, so it did not live out its life.

Michael, the glass on the lamp had started turning black and the anode and cathode ends had started turning blue.
The arc did not appear to wander when viewed from the sight glass.
Checking the stabalising magnet was mentioned in a different thread and is unrelated to this problem.
The arc was never actually weak on any lamp in this lamphouse.

Posted by Pat Moore (Member # 380) on 02-20-2003, 06:36 PM:

Hi James; I'm not a fan of that digital readout either. We do have a conversion to put the anlog setup in the console. I don't have a part number or price handy (I'm in Asia right now) but they are available.

Definite seal failure if the lamp turned blue. Apparently it's life was only 300 hours [Wink]

.

I would be suspicious of cooling problems. That big fan on top of the console seems like a great air filter sometimes. Cleaning that will improve overall air flow, as well as cleaning the front seal blowers. Take a look at the ducts on the frnt blower and be sure air is directed over the lamp anode from one, and over the reflector on the other. Exhaust from the console should be in the 400CFM range for that wattage of lamp.

Pat