Film-Tech Forum ARCHIVE: Why is my arc so weak?

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Posted by James R. Hammonds, Jr (Member # 673) on 02-18-2003, 11:25 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.

We have the same problem in two different houses, separate from the house mentioned in my other post about bad lamps and power readings.

We will put in a new lamp and will get the correct power reading from the power supply.
The light on screen will be good for the most part, but not quite as good as it should be.
Instead of having a nice big bright arc that would blind you if you look at it for too long through the sight glass, we have a small puny arc that just looks too cute to look away from.
Seriously, you could cuddle with this thing.

After a couple hundred hours, the picture will dim considerably and will start to flicker.
By the time you get to 500 to 600 hours, we usually have ourselves a really nasty flicker, unlike what you might expect in other houses.

Everything Ive looked at visually looks ok.
Any ideas on what might be causing this and what we can do to correct it?

Posted by Paul G. Thompson (Member # 655) on 02-19-2003, 12:13 AM:

I think it is time to get your lamphouse voltmeter and ammeter calibrated. Sounds like you are badly underpowered, even though the stupid meter says you are ok. That's a start....

Posted by Adam Martin (Member # 641) on 02-19-2003, 03:07 AM:

Drink more water. If that doesn't work, try holding it in longer.

Edit: Oh. You're talking about your lamp arc. I never was really thrilled with high-power Osram lamps. They always seemed to start flickering around 500 hours. Have you tried another brand (like Christie, which makes a better high-power lamp in my opinion) in that lamphouse?

Posted by James R. Hammonds, Jr (Member # 673) on 02-19-2003, 03:32 AM:

Paul,
I don't trust the display board for that information.
We have the lovely Strong digital display boards that aren't worth a [bs]

I take all the power readings on all lamphouses with a clamp on meter.

Adam,
We havent had a different brand bulb in there in a while, but I have only noticed this problem since we started using the OSRAM lamps.
We do have 4 other houses running the exact same lamps, but those have the nice srtong arcs rather than the weak ones we have in these two.

Posted by Kenneth Wuepper (Member # 1174) on 02-19-2003, 07:09 AM:

James,
Have you checked each of the phases of your primary AC supply? I can imagine that there is a possible loose connection there if more than one lamphouse is having the same problem.

KEN

Posted by Michael Schaffer (Member # 1204) on 02-19-2003, 08:03 AM:

I am not very familiar with this type of lamphouse but logic tells me it should also have a magnet to stabilise the arc. Maybe the magnet is misaligned. This could also explain the premature aging. I never had any problems with Osram lamps (except for one which exploded). If you treat them well, you can use them much longer than the guaranteed hours.

Posted by Jack Ondracek (Member # 1466) on 02-19-2003, 09:26 AM:

James, we just had this problem in one of our Super Lume-X's.
Over the course of two shows, I watched our image get progressively dimmer, the "arc" start wandering all over the place & the current readings go down to about half what it should have been.

Keeping it short (yes, we checked everything)... it turned out to be a bad weld on one of the endcaps on the bulb itself.

A new bulb fixed the problem, and we've got the old one going in on warranty.

(edit)
If you're sure the lamps don't start out as good as you think they should, it almost sounds like you've got a power supply problem killing the bulbs.

You didn't say what the anodes look like when you pull the bulb out. After 600 hours, they should still look pretty good, unless something's going on in the supply.

Posted by Greg Mueller (Member # 17) on 02-19-2003, 10:26 AM:

How accurate should one expect the ammeter to be on the back end of a Super Lume-X ?
The one I have says that it's getting 50 amps, but my power supply is on it's lowest setting. This PS is an LP & Assoc 8501 and shouldn't be able to do much more than this on it's highest setting. So how can I measure the amps other than the meter on the back of the Super Lume-X ?

Posted by Pat Moore (Member # 380) on 02-20-2003, 06:43 PM:

Greg; Those ammeters were reasonably accurate. I don't know what the designed tolerance is, but I don't remember any larger discrepancies over the years. The easiest way to check is with a clamp on ammeter. A little trickier would be to read the actual voltage drop across the shunt. Again, I don't remember the specifics but it's stamped on the shunt, or you could call Strong and get the details. It will be something like this: for a reading of 100 Amps, the voltage drop will be 50mV -- something like that. If you read 25mV across the shunt, that's half maximum reading or .5 x 100 = 50Amps on the lamp.

Pat