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Author Topic: Protecting xenon bulbs in power failure Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 03-01-2005 08:54 PM                     I'm only guessing but there might be a small increase in temperature right after the fan(s) go off. The heat radiating from the interior of the lamp gets blown away by the air flow but suddenly cutting off the air flow might allow heat to build. I can't imagine that the heat would be detrimental. Like you said, the lamp isn't PRODUCING more heat. The heat that's inside is just equalizing throughout it.  |  IP: Logged Jarryd Beard Expert Film Handler Posts: 229 From: Hellertown, PA Registered: Jul 2004 posted 03-01-2005 09:33 PM                     But also keep in mind, the fan isn't suddenly stopping. As the fan decreases in speed, it's still moving air. I know that after I've power down for the night, the fans can still be heard whirling down slowly.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 03-02-2005 12:52 AM                     actually ther is a very large temp increase if the lamp shuts of and the fan switchs off The total energy of the lamp has a peroid of time to disipate that is a constant if the cooling flow is interupted I used to have a graph of it  |  IP: Logged Wolff King Morrow Master Film Handler Posts: 490 From: Denton, TX, USA Registered: Feb 2004 posted 03-02-2005 04:47 AM                        quote: Randy Stankey In my booth, I split the difference. I shut off the forced cooling fan inside the lamphouse but I leave the roof exhaust turned on. Question: Do you do this after each show ends? Wouldn't you have to constantly run around shutting fans off as soon as movies dropped in say an 18-screen multiplex? If it's only done at night, then I'd say the advantage gained would be negated by all the sets in between.  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 03-02-2005 09:23 AM                     We only do two or three shows per day. It's not a problem for me to shut them off on in-betweens. Yeah, if you are in a googolplex it would be a pain to shut them off all the time.  |  IP: Logged David Buckley Jedi Master Film Handler Posts: 525 From: Oxford, N. Canterbury, New Zealand Registered: Aug 2004 posted 03-02-2005 04:25 PM                        I dont know a huge amount about lamp physics, but do not a bit about keeping (big) electronics cool, and thermal pathways. If you turn off the heat source (lamp arc) and the heat removal source (cooling air) simultaneously, things between the two and around them will not necesarily not get hotter. The heat source may vanish immediately the power is removed, but things very near to it are still hot. Thus stuff inbetween and around (bulb envelope, metal of lamphouse) will still be receiving heat from the elctrodes of the lamp, but not having the heat removed by the cooling air. Thus their temperatures could increase before they fall. Although the electrodes may not have the thermal intertia for this to be noticable, I dont know that. On the other topic - I do know a lot about electricity, and if you have a three-phase load that requires all three phases, there should be a phase failoure detection relay in the control circuit. I dont know about the USA, but in the rest of the world, all small threephase motors are connected to a Direct Online Starter (DOL) which is the box with the red and green buttons, and these detect overload or any phase going undervoltage, and switch off. Inverter driven motors are also protected by similar logic, but electronic rather than thermal-magnetic. If you've got A/C systems getting harrassed by phase failure, you've got big problems. It should just shut down abuptly.  |  IP: Logged Rich Granata Film Handler Posts: 61 From: Bethlehem PA USA Registered: Mar 2004 posted 03-02-2005 05:38 PM                     So what the verdict? I might be up all night pondering thermodynamics. My theatre policy has always been to let fans run for 15 minutes. What do the lamp manufactures say?  |  IP: Logged Dennis J. Losco Film Handler Posts: 39 From: Phillipsburg, NJ, USA Registered: Jul 2002 posted 03-03-2005 08:48 AM                        Absolutely leave the fans running!!!! The anode is approx 2000degrees C. The quartz body is 700 degrees C. The radiant heat from the anode will continually heat the quartz body beyond recommended temperatures. Forced air is essential on the cool down stage. A power outage is awful for the lamp. Without the proper cooling additional stresses will be created within the quartz wall. A chance of an explosion will increase dramatically. It could happen immediately or the stresses will slowly increase over time and explode later down the road.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 03-04-2005 09:20 PM                        Our Osram lamphouses won't let you turn the fans off with the bulbs. You can turn all the power off to the lamphouse and the fans will keep running for about 15-20 minutes on a thermal switch, no matter what, short of your turning off the breaker. These guys make the lamphouses and the bulbs, you gotta figure they know what they are doing.  |  IP: Logged Floyd Justin Newton Jedi Master Film Handler Posts: 559 From: Phoenix, Arizona, USA Registered: Jun 2002 posted 03-04-2005 09:31 PM                     Right on, Frank. It's just damn near impossible to convince some people of that!  |  IP: Logged

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