Film-Tech Forum ARCHIVE: bonehead mistake may have overheated bulb?

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Posted by Steven J Hart (Member # 2340) on 08-08-2008, 08:03 AM:

Like a retard, I screened my print of Dark Knight last week without turning on the external lamp house blower. I'm running a Kneisley Xenex II with a 1600 watt bulb. The airflow from the internal blower was enough to trip the airflow switch on so the lamp ignited and ran for 2.5 hrs. The bulb has about 450 hrs on it. Should I replace it or do you guys think it will be ok?
Steve Hart

Posted by Sean McKinnon (Member # 612) on 08-08-2008, 10:41 AM:

Well, The excessive heat could have damaged the seals and increased the chances of a catostrophic lamp failure (Explosion).

On the other hand, there are a lot of theatres that do not run with the proper cooling and dont blow up thier lamps. While my official reccomendation would be to change it, you may want to evaluate the light on screen. If you do not see any wavering, or loss of light output you may want to continue to run it. However, if it does explode and takes out your reflector you may not be able to have it replaced under warranty if they find that the lamp failure was dur to excessive heat.

Posted by Randy Stankey (Member # 64) on 08-08-2008, 12:21 PM:

The fan in the stack only vents the excess heat out of the building. As long as you have good airflow within the lamphouse and around the lamp you should be okay.

Some lamphouses need to be vented to prevent heat buildup but, generally, as long as the lamp itself is kept cool, you will not have problems if this is an isolated incident.

Check the lamp for signs of overheating. (Discolored ends, etc.)
If everything looks okay, there's no reason you shouldn't get a normal lifespan out of the lamp as long as you're careful not to do that again.

Posted by Barry Floyd (Member # 385) on 08-08-2008, 02:03 PM:

Like the others have said, unless you see a noticable degredation on the screen, I'd run with it.

I've got a Xenex II with a 4kw Osram in it and one night forgot to turn on the external exhaust fan on a 4 1/2 hour double feature at my drive-in. I freaked out, but the bulb ran fine afterwards.

I've gotten 3 full seasons out of that one bulb, and it's finally getting changed out on Monday night.

Posted by Steven J Hart (Member # 2340) on 08-08-2008, 05:24 PM:

Upon inspection, the envelope of the bulb shows no sign of darkening, and light is great on the screen. I think I'll run with it. Thanks for the advice.
Steve

Posted by Mark Gulbrandsen (Member # 72) on 08-08-2008, 07:23 PM:

I can guarantee you that you didn't hurt it running just that duration. I've run that same lamphouse portable a number of times with just the internal blower. Not only is the Xenex 1 mirror easy on a lamp but the internal blower is almost enough to cool a 1600 watter by itself. I do however reccomend that you install an airflow switch on your exhause stack and wire that switch in series with power switch or with the rectifier contactor control coil. This will ensure the lamo is bnever run without the stack cooling.

Christie makes a stack switch kit that is actually a replacement kit for the SLC console. The kit has everything you need including the bracket, switch sail and really long leads to reach just about enywhere you need to go within the lamphouse itself. Costs about 40 bucks.

Mark

Posted by Anslem Rayburn (Member # 1267) on 08-09-2008, 01:38 AM:

quote: Steven J Hart
The airflow from the internal blower was enough to trip the airflow switch on so the lamp ignited and ran for 2.5 hrs

Posted by Jack Ondracek (Member # 1466) on 08-09-2008, 10:07 PM:

I had somewhat of a catastrophe last week. One of my exhaust fans quit, which caused a damper to close, pretty much sealing up the lamphouse. By the time I caught it, the whole back support assembly had melted. It took over an hour before I could touch anything in there.

Big Sky overnighted a new assembly. I had to take a blowtorch to the back of the bulb (well wrapped) to get it out of the lamphouse. Everyone's amazed the thing didn't blow up, taking a glass reflector with it.

Live and learn... The internal blower in the Big Sky L5 has a vane switch, but there's nothing in the stack. I did a "safety workaround", I thought, by using the exhaust fan's 120 volt supply to feed the control input of the power supply. The idea was, no voltage to the fan, no control voltage for the lamphouse. I didn't plan for what would happen if the fan motor conked out.

After looking the bulb over, I decided to retire it. It was new this year, which might be the only thing that kept it from exploding.

Haven't bought a separate vane switch in a long time. Wonder if that Christie switch can be fitted on a Big Sky??

Posted by Jeremy M Smith (Member # 4913) on 08-10-2008, 12:26 AM:

in one of our cinema's we have the bulbs only 600 hours at best it has all the signs of it overheating but we have replaced all the fans even the rectifier thinking it was ripple. but never had a bulb blow up yet (touch wood) and it has been doing it for about 4 years. So I say if the bulb looks fine stay with it you may just not get the hours you wished out of the bulb

Posted by Jack Ondracek (Member # 1466) on 08-10-2008, 01:19 AM:

I appreciate you thought, Jeremy. What makes me nervous about running that bulb is the reflector. It's glass, and about $2,000. If I lose a bulb (which I've already replaced), I'd have to add the cost of the reflector, too.

The wife says, if I put that bulb in and it blows, the cost comes out of my avgas budget. That's about 42 hours of flying, at today's prices.

Wife wins! [beer]