Film-Tech Forum ARCHIVE: Xenon bulb run settings

This is topic Xenon bulb run settings in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Monte L Fullmer (Member # 2797) on 10-20-2005, 04:07 AM:

Okey, I'm going to be a "newbie" here again, for this has me wondering on this for quite a while:

I'm playing with STRONG switchers with the AMP/VOLT rocker switch on the console. My bulbs are the 2k variety.

(And this could also be in play with reactance rectifers as well..)

I look in the spec sheet that comes with a bulb (and in other manuals) on the recommended run of AMPS and VOLTS for a bulb - any make of bulb.

For example: a 2k bulb usually has the run specs of between 25 to 32vdc with the amp run between 60 and 85amps.

Now, when bulbs are placed in new, you usually get the voltage readings a bit lower than the 25 when running at 70amps

Then, when bulbs has quite a bit of age (like 3500hrs), voltage run is about 32vdc for a 75amp run. Granted, the spec sheets also mention of removal of bulbs when they reach 150% of their life. Just that I've got some bulbs not too much over 4k that still look good, but are running these "V/A" figures somewhat high.

Now, if we take our famous "PIE" (P=IxE) math with "P"=Wattage, "I"=amps, and "E"=volts, 32vdc times 75a is gonna equal 2400watts of power coming from the rectifier to run that bulb.

Now, being the 2400 watts, it looks like were 400 watts over the recommended rating for the bulb. But, the amps is 10 amps BELOW than the maximum rating for the bulb. Just that the voltage has risen to push the wattage of the bulb over the recommended rating.

If I crank down the amperage to 65 amps (course, I start losing some light with lesser amperage), then I can get under the 2k rating for the bulb since I'm also dropping the voltage and still stay over the recommended 80% recommended operational run. But, then the bulb has a hard time striking with multiple pulses to ignite the bulb.

Conclusion: do I use the "PIE" method for proper usage, or use what the spec sheets say about amperage alone...

thx for the help - Monte

Posted by Richard May (Member # 2627) on 10-20-2005, 08:41 AM:

It's probably wrong, but I have always gone by the amperage readings. As the bulbs get older, I increase the amperage slightly. We get way over the recommended life of our bulbs. On average, we get about 7000-8000 hours before we change them. Even then, we only change them because we can just barely get 16FL in the center and about 11 or 12 on the sides.

Posted by Gordon McLeod (Member # 33) on 10-20-2005, 09:46 AM:

The voltage drop will increase slightly as the electrode gap lengthens over the life of the lamp and as the coating on the electrodes that aids emmision is lost

Posted by Peter John Anthony. C (Member # 2500) on 10-20-2005, 12:15 PM:

"PIE" (P=IxE) math with "P"=Wattage, "I"=amps, and "E"=volts.

I follow the above calculation, if the illumination gets low or if the lamp takes hard to strike ON. i just replace the lamp.

Posted by Louis Bornwasser (Member # 3063) on 10-20-2005, 03:00 PM:

Amperage is not relevant. There will always be some variation even between identical same-branded bulbs. Gas pressure, etc changes this. Compute your WATTAGE and act accordingly. Do not exceed any idividual parametewr.

All lamphouses shoudl have direct reading watt meters. This is not difficult with digital everything.

Louis

Posted by Tim Reed (Member # 137) on 10-20-2005, 10:33 PM:

What Gordon said.

Just like in a carbon lamp... the wider the gap, the more it approaches being an "open circuit", if you will, so the voltage naturally increases across the arc.

FWIW, most bulbs will take a heck of a lot more than you might think, though I personally wouldn't chance it.

Posted by Richard Hamilton (Member # 321) on 10-21-2005, 11:51 AM:

Monte,
Just a suggestion, I would also double check the readings with a meter. On the consoles, the analogue meters are better than the digital ones, but I would take both readings with a meter. I am not sure if i have ever seen an accurate meter, or one that was calibrated from the factory.

Rick