8mm Forum: ELMO ST1200HD LAMP VOLTAGE

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Topic: ELMO ST1200HD LAMP VOLTAGE

Gary Crawford
Jedi Master Film Handler

Posts: 979
From: Manassas, VA. USA
Registered: Jun 2003

posted November 19, 2009 02:37 PM

I am inquiring of the elmo experts here for a friend of mine. He has been testing several 1200Hd's recently...and is puzzled by one thing. He's been measuring voltage going to the lamp. With the drive not running..just the motor, he's getting the advertised 15 volts. With the projector operating...voltage is cut down to 14. He's checked voltage going into the house..and it's right on the money. Turn of the drive of the machine, voltage back up to standard 15 volts. He says the difference of a volt on the bulb can make considerable difference in brightness. He asked me to ask you guys if this reduction is generally true of all the machines of that model. He's tested three or so and found it happening in all of them. finally he wanted to know if there's anything one could do to get that voltage going to the lamp back up to 15 volts. He has cleaned the contacts and all that already. thanks for any light, so to speak, that you can shed on this.

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Steve Klare
Film Guy

Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003

posted November 19, 2009 03:27 PM

If you get in your car, turn on the engine, turn on the headlights and then turn on something big like the air conditioning, the headlights will dim because the additional load is pulling the system voltage down.

This is the same thing. Since the lamp voltage is not actively regulated there's not really a lot you can do.

Since it is unregulated you want the maximum voltage on the lamp to be the rated one (or even a little less...), so you never go higher. This means the lamp voltage sinks down from rated. As long as the difference isn't annoying, it's OK.

--------------------
All I ask is a wide screen and a projector to light her by...

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Joerg Niggemann
Expert Film Handler

Posts: 127
From: Germany
Registered: May 2006

posted November 20, 2009 10:32 AM

I found the following rules for halogen bulbs on the german Osram website:

Reduced voltage of 5% will result in a loss of light output of 15% and increased lamp life of about 50%. The other way round, increased voltage of 5% will give you 15% more light and 50% less lamp life.

--> 14 instead of 15V lamp voltage means nearly 7% lower voltage and estimated 20% less light output, which is significant.

The lamp voltage of my ST1200 (which is no "D" or "HD") is always 15,4V in the "high" position, independent of the drive running or not. Maybe the HD design is different?

Joerg

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