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Topic: Bulb or Lamphouse Problem????

Michael Schaffer
"Where is the
Boardwalk Hotel?"

Posts: 4143
From: Boston, MA
Registered: Apr 2002

posted 08-10-2006 12:29 AM

I don't know if this has been mentioned before, but in addition to the things discussed above, a look should also be taken at the reflector. Sometimes when the reflector gets old and the reflective coating hazy or even starts to come off in tiny flakes, the light output is bad and since the dichroic properties of the coating are lost, it gets much hotter inside the lamphouse than is good for the lamp.

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Don Anderson
Master Film Handler

Posts: 312
From: West Bend, WI, USA
Registered: Mar 2000

posted 08-10-2006 01:15 AM

Gordon- The lamphouse that were are having problems is vented from the back of the unit.

Mike- I installed a brand new reflector in the 2500S about 1 1/2 years ago. So, that's not the problem. But, I could use a new reflector in one of the lamphouses in the main floor both!

Mark- The electrican is a friend of mine, he actually did it fairly cheap. He also wired up our outlets for our digital screen advertising setup which was more of a pain than the 3 phase. he ran a line up from the lower level booth, under the balcony seating and into the booth. Did it in about 2 hours. I had to explain to him what needed to happen when the digital was powered up, and what it was to do upon the automation kicking in. Works like a charm!

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 08-10-2006 09:14 AM

quote:
To ME, it is not that easy. I emailed you with another question about the selection of diodes and you never responded, so I am still stuck. Perhaps it will just come to me one day and I'll go back to that site and order the hell out of the diodes...but until I get struck with that information OR someone is patient and answers questions, I'll continue to have my company pay $30 a piece. Thanks for the help!

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Sorry Frank but out of respect to other dealers here that also sell them I can't post that info. I'd be happy to explain in great detail to you the space shuttle main engines start sequence if that would be of any help...... [Cool]

.

"The HPOT consists of two single-stage centrifugal pumps (a main pump and a preburner pump) mounted on a common shaft and driven by a two-stage, hot-gas turbine. The main pump boosts the liquid oxygen's pressure from 422 psia to 4,300 psia while operating at approximately 28,120 rpm. The HPOT discharge flow splits into several paths, one of which is routed to drive the LPOT turbine. Another path is routed to and through the main oxidizer valve and enters into the main combustion chamber. Another small flow path is tapped off and sent to the oxidizer heat exchanger. The liquid oxygen flows through an anti-flood valve that prevents it from entering the heat exchanger until sufficient heat is present to convert the liquid oxygen to gas. The heat exchanger utilizes the heat contained in the discharge gases from the HPOT turbine to convert the liquid oxygen to gas. The gas is sent to a manifold and is then routed to the external tank to pressurize the liquid oxygen tank. Another path enters the HPOT second-stage preburner pump to boost the liquid oxygen's pressure from 4,300 psia to 7,420 psia. It passes through the oxidizer preburner oxidizer valve into the oxidizer preburner and through the fuel preburner oxidizer valve into the fuel preburner. The HPOT is approximately 24 by 36 inches. It is attached by flanges to the hot-gas manifold."

As for the diodes I guess you could purchase them from
another dealer that stocks them and then you'd have the type number... there.... that wasn't too hard to figure out was it...

Mark

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Dave Barker
Film Handler

Posts: 2
From: Nashville, IL / USA
Registered: Jun 2006

posted 08-10-2006 01:03 PM

From an electricians point of view, current(amps) and Voltage(volts) are inversely proportional. When you limit the voltage it will raise the current until the demand is satisified or until the limit of current is reached. If normal operating voltage on an arc lamp is 24 volts and normal operating current is 65 amps you can take the volts and multiply that times the amps and get 1560 watts. Reasonable for a 1600 watt lamp, should light and burn bright.
Now limit the voltage using some type of flaw or failure in the supply leads, rectifier, incoming voltage, whatever the case might be, even if you deteriorate a connection between the lamp and the supply output. The leads may not be very long and just measureing with an ohm meter wont discover a resistance that could cause limiting under a high current condition. Also if any of the connectors or the leads were sized too small in a replacement procedure it could be causing more resistance to bring that voltage down as well. So you say we have reduced the voltage down to 12 volts now? Not exactly 12 volts but for the sake of explanation and easy math. What just happened to the current (amps) demand? You are asking a power supply that is rated at perhaps 80 amps to give you DOUBLE what you had before. 12 volts x 130 amps is guess what...1560 watts....... The power supply can not take the required load so your output is reduced in your lumens that actually reach the screen.
Now the reason for the lamp failure could be the high current that is causing deeper than normal pitting and also heating up the lead ends that would cause even higher resistance and more heat. This in turn could cause minute fractures of the glass envelope that would let air in causing a "milky cloud" coating on the inside of the lamp. (This is where you get dangerously close to exploding a zenon lamp inside a housing that will shatter a glass reflector.) So it acts like an airflow problem but actually is supply.
So why are they failing so soon and new lamps dont experience the same problem if it is a supply flaw? The only thing on a lamp that changes over its life under even perfect conditions is the electrodes. Pointy end (laymens term) gets pitted and shortened and the bulky end gets all kinds of speckles of material that came from the pointy end's pits. This changes the distance between and the surface structure of the two arc surfaces which changes the pattern in the arc as well as the wattage.
Why does the wattage go up instead of down when light is less? If the 'trodes are closer together from the raised surfaces, the resistance is lower and the arc pattern will be narrower in shape. Less arc, less light. If you've ever done any arc welding this will be easy to comprehend.
So you want an answer not a math and electrical survey of what you already know is not working? Double check EVERY connection, follow EVERY wire, look for excess heat at connections, remove connections one at a time and inspect and clean them carefully, scrape them to bare metal if there is any discoloration, factory crimps are ok but if you have any field crimps check them they should be rock solid with no movement in the wire. Also double check that the proper diodes for your rectifier are being used. If you got those used, you may have something that was someone elses nightmare that was modified outside of factory specifications.
What might have changed to start this problem now and wasnt doing it before? Could be an indication of a problem in the AC supply leading to your supplies that only shows under load. Have current checks done on all 3 legs of the 3 phase to make sure they are even. Your electrician can do this with an Amprobe. Do it over a period of time during operation measured at the rectifier where the power comes in so no other equipment is measured. If you have an imbalance that can cause abnormal voltages on the lamp supply as well.
Seems to me your startup voltage is ok at 20 to 22 volts but it should gradually run up to 25 volts after 5 minutes. It might be that you do need to "pump up the transformer" jumper bars on the AC side for the correct voltage supply. 3 phase is 3 phase but there are different variations on voltages. The variations of 208, 220, 230, and 250 volts are enough to cause a lower voltage at the DC side.
You might get less damage to your lamps at startup if you had a higher voltage that could start arc quicker than if you use a lower setting for your 1600 watt lamps.
Well I am drained, good luck. Just remember, all the obvious things that may be overlooked. You might be looking for a haystack and not the needle.

Dave

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Frank Dubrois
Jedi Master Film Handler

Posts: 896
From: Cleveland, OH
Registered: Mar 2005

posted 08-10-2006 01:23 PM

quote: Mark Gulbrandsen
"The HPOT consists of two single-stage centrifugal pumps (a main pump and a preburner pump) mounted on a common shaft and driven by a two-stage, hot-gas turbine. The main pump boosts the liquid oxygen's pressure from 422 psia to 4,300 psia while operating at approximately 28,120 rpm. The HPOT discharge flow splits into several paths, one of which is routed to drive the LPOT turbine. Another path is routed to and through the main oxidizer valve and enters into the main combustion chamber. Another small flow path is tapped off and sent to the oxidizer heat exchanger. The liquid oxygen flows through an anti-flood valve that prevents it from entering the heat exchanger until sufficient heat is present to convert the liquid oxygen to gas. The heat exchanger utilizes the heat contained in the discharge gases from the HPOT turbine to convert the liquid oxygen to gas. The gas is sent to a manifold and is then routed to the external tank to pressurize the liquid oxygen tank. Another path enters the HPOT second-stage preburner pump to boost the liquid oxygen's pressure from 4,300 psia to 7,420 psia. It passes through the oxidizer preburner oxidizer valve into the oxidizer preburner and through the fuel preburner oxidizer valve into the fuel preburner. The HPOT is approximately 24 by 36 inches. It is attached by flanges to the hot-gas manifold."

See, and I thought it was just a matter of counting down from 10 to 1. I don't spose you'd let me know where I can find a oxidizer preburner oxidizer valve?

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 08-10-2006 02:26 PM

Sure,

Just contact Rocketdyne... be sure to have the serial number of your engine handy so you get the correct version of the valve... [thumbsup]

Mark

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Eric Robinson
Jedi Master Film Handler

Posts: 538
From: Santa Rosa, CA
Registered: Jan 2005

posted 08-10-2006 05:07 PM

As a sidenote, if one were to measure the dc voltage from the positive output terminal to the positive connection at the bulb, while the bulb is lit, ideally you would measure zero volts becuase the conductor from the supply to the bulb would have close to zero ohms resistance (in a perfect world.) Therefor, since the conductor is of good quality with very low resistance, it will not drop any voltage. The same goes for the negative conductor from the supply to the bulb connection. There may of course be some obstacles in the path such as a shunt or ignitor which may show that a small voltage is present though.

Although you mentioned that you have several different versions of equipment, you could compare voltage measurements as I described above between two similar lamphouses running at roughly the same output. This can be tricky though because firstly it would require you to place a measurement lead at a bulb connection and the lead wire must not be too close to any other metal during the ignition phase. Also the dvm leads can not be connected to the DVM during ignition due to the high voltage discharges during ignition which would likely kill your DVM.

In conclusion, this is probably a horrible idea to try, but it would illuminate any possible unsuspected voltage drops in your DC electrical path.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 08-10-2006 05:40 PM

quote: Eric Robinson
As a sidenote, if one were to measure the dc voltage from the positive output terminal to the positive connection at the bulb, while the bulb is lit, ideally you would measure zero volts becuase the conductor from the supply to the bulb would have close to zero ohms resistance (in a perfect world.) Therefor, since the conductor is of good quality with very low resistance, it will not drop any voltage. The same goes for the negative conductor from the supply to the bulb connection. There may of course be some obstacles in the path such as a shunt or ignitor which may show that a small voltage is present though.

Actually there exists cyrogenically cooled cable that comes pretty close to that perfect wire theory. Its used in particle accelerators and physics expereiments that are done on huge scales....

Mark

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