Film-Tech Forum ARCHIVE: Bulbs fusing in the lamphouse

This is topic Bulbs fusing in the lamphouse in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Michael Rourke (Member # 1142) on 05-31-2003, 01:53 PM:

I have had incredibly bad luck with bulbs fusing in my lamphouses. This has happened in the SLC-20 and 30's at the 7 plex I work at and it has happened in the brand new SLC-45/70 I run and more appropriately, it has happened in the CC-20's that are older than me. I think it has been a combination of bad batches of bulbs, inadequate exhaust, and pushing bulbs too long.

Back when I first started at the 7 plex we used Osram bulbs, rotated at half life, and the exhaust fans were newer and we never had a bulb fuse. Then we started using ORC bulbs and stopped rotating and have had reoccuring problems ever since.

Since the bulbs have fused in each lamphouse I have tightened up all the connections, added a stack booster fan, serviced the existing exhaust fan and in one case replaced the exhaust blower and motor. I had a bulb fuse last night in a 3K lamphouse that has more than enough CFM, the bulb was a Christie XBO and had 1500 hours on it. Even til the end it was running at 97-98A and 27V.

I was told to really clamp down on the allen cap screw on the negative end threaded clamp so the bulb couldn't move at all, but it seems to me that when the bulb gets hot it will want to expand and have no room to and will fuse to the clamp.

I appreciate any input you guys have on similar experiences, and maybe some things you do when changing bulbs that I might be overlooking, should I be cleaning the contacts everytime? Thanks for your help.

Posted by Brad Miller (Member # 2) on 05-31-2003, 02:00 PM:

quote:
I was told to really clamp down on the allen cap screw on the negative end threaded clamp so the bulb couldn't move at all, but it seems to me that when the bulb gets hot it will want to expand and have no room to and will fuse to the clamp.

Yes, clamp down good and tight or you will continue to have those problems.

Posted by Michael Rourke (Member # 1142) on 05-31-2003, 02:17 PM:

I was told that by Christie techs I should say. Sometimes when I have replaced the clamp and screwed in the new bulb I will tighten down the allen screw with the bulb wrench until it won't move anymore but the bulb can still rotate...is that too loose or is that okay?

Posted by Brad Miller (Member # 2) on 05-31-2003, 02:29 PM:

Not good. When you tighten down the allen screw, you will not be able to rotate the bulb. If you can, something is wrong.

(By the way, whenever you decided to "test" out how tight it is, NEVER rotate the bulb by the anode end. It amazes me that people do that. It's just begging for a bulb to explode in your face from the stress. Grip the cathode end and verify it is snug.)

Posted by Jean-Michel Grin (Member # 1360) on 05-31-2003, 04:29 PM:

Here is an example of realy bad focusing [Big Grin]

Guess what ? The mirror was bendt at his back. I really dislike the Hightlight console

For the problem of overheating in a lamphouse, I've experienced the same with an another Highlight console [Mad]

The problem will appears like this: Impossible to achieve an good light focusing on the screen and with the heat, the mirror losed his coating.
The console was so hot that You could cooking some eggs on the top of the lamphouse or heating Your meal, Pizzas, Mc Donalds meal or anything You wanted [Big Grin]

I've tried this once time, my lunch was perfectly cooked ....

To achieve the light out of the lamphouse I checked the two lamps: At this time we switched from ORC to Osram. We discovered that the osram lamps have a munch bigger size than the orc one, and the carriage who move the anode canot be moved away enough to focusing the bulb on his right place.
The only solution was to make an adaptation of the anode carriage, in this case drilling three new fixing holes, to place it more away of the mirror. With that, I achieved a great Lamp focus, and a better projection result.

Try to check the distance between the film and the back of the mirror. maybe wrong ?

In hope that can help , If You can understand my weak English ! [Smile]

Bye,

Jean-Michel

Posted by Chris Markiewicz (Member # 1415) on 05-31-2003, 05:22 PM:

Try pulling the allen screw and see if the "working" end is worn down. If the taper is worn off the screw it will slip on the cathode threads.

Posted by Bruce Hansen (Member # 281) on 05-31-2003, 06:41 PM:

Make sure your connections are clean. A dirty connection will cause resistance, and resistance will cause heat, and 98 Amps can sauce a lot of heat. This could be causing your problem.

Posted by Gerard S. Cohen (Member # 994) on 05-31-2003, 08:10 PM:

Michael,

Perhaps when the suggestion to rotate bulbs at half-life or quarter-life was made, you thought the clamps needed to be loose to permit rotation. Not so! To make proper electrical contact, connections must be clean, bright and TIGHT. If loose, they will arc at the connection , which will fuse--actually, weld.

To accommodate bulbs of various lengths, manufacturers provide
tubular adaptors with set-screws. Also, some lamphouses require
triangular "spider" supports to be used with some bulbs on the
anode end, which may have two cables supplying current, not the usual one.

Make sure your lamphouses are not focusing the heat and light on the anode connection instead of on the film aperture.

Gerard

Posted by Richard Fowler (Member # 893) on 06-01-2003, 05:03 AM:

D.C. connections....xenon bulb...rectifier points...your car battery always required maximum tightness. Most bulb clamps are nickel plated brass which can wear down and loosen with multiple bulb changes. To save a clamp I have had to use a lock nut on the allen screw on some units to restore tightness. It is good to use a minute ( very small ) amount of silicone ( electrically conductive ) spray on allen threads and interior contact surfaces of some clamps to lessen fusing of contacts to the bulbs.
Richard Fowler
Kinoton America Inc.