8mm Forum: EFP bulbs and how to power them

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Topic: EFP bulbs and how to power them

Jan Bister
Darth 8mm

Posts: 2629
From: Ohio, USA
Registered: Jan 2005

posted July 03, 2005 06:31 PM

One more, then I'll stop with my outlandish questions, promise [Big Grin]

OK, I know EFP bulbs are rated 12V/100W, that is, they consume about 8.5 amps. My question is, is the voltage AC or DC, and if it's DC, is it pulsing or continuous? Does it matter which way the bulb is connected to plus and minus (polarity)?

I want to try and plug an EFP bulb into a computer power supply's 12-volt rail (that rail being rated at 18 amps, so plenty of headroom there). If this works, my next step shall be converting my B&H Filmosonic 600 machine to run on EFP instead of DJL bulbs. [Smile]

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Call me Phoenix. *dusts off the ashes*

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Steve Klare
Film Guy

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

posted July 03, 2005 09:52 PM

Hi Jan,

The bulb is basically just a resistor, so it doesn't really care about polarity, waveform or frequency (...within certain reasonable bounds!)

Generally AC is specified in Volts and Amps RMS, which are DC equivalents, so 12V RMS AC and 12Vdc will give the same power through the same lightbulb.

One benefit of powering a lightbulb from a DC power supply is many DC power supplies are current limited, and would hold down the surge current on startup. This could extend the life of the bulbs.

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

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John Whittle
Jedi Master Film Handler

Posts: 791
From: Northridge, CA USA
Registered: Jun 2003

posted July 03, 2005 10:44 PM

Jan
Keep us posted on your results. While most projectors used an autotransformer and AC to run the lamp, it was just the technology of the times. I bet if they were doing it today, they'd use a switching power supply to run the lamp since it wuold be cheaper than a transformer big enough to supply the amperage and would adapt easily to various mains sources and frequencies.

I think the "older" AT supply would be an easier choice than the current "ATX" supply since the ATX needs a resistor and start up sequence whereas the AT supply will start with the power switch.

There are also lots of other "power supplies" for various voltages and amperages available from surplus dealers such as All Electronics Corp in Van Nuys CA (I think it's www.allelectronics.com).

John

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Josef Grassmann
Expert Film Handler

Posts: 190
From: Hennef-Sieg, Germany
Registered: Apr 2005

posted July 07, 2005 03:43 PM

As far as I remember there had been done many life-time tests on projection bulbs.
If they are powered by continuous DC the expected life will be less compared to AC. Maybe 5-15% less.

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Steve Klare
Film Guy

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

posted July 07, 2005 04:49 PM

Interesting!

Any theories why?

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

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