Film-Tech Forum ARCHIVE: Rectifier setting: am I mistreating my lamp?

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Posted by Thomas King (Member # 2745) on 11-07-2004, 10:20 AM:

I've got an Osram XBO 2kW lamp (I'm not sure of the exact model number, I can find it out if need be). The website gives specs for the 2k XBO lamps running at 70A mostly, with a couple running slightly higher. Our rectifier just has an ammeter, and currently runs at 50A (turns out we used to run 1.5kW lamps until last year). If I find out the rated running current of my lamp, is it just a question of turning the imposing knob on the rectifier until the current is correct?

Posted by Steve Kraus (Member # 476) on 11-07-2004, 10:26 AM:

Possibly/probably but it would help if you let us know what make and model of rectifier. "Imposing knob" sounds like you have IREM's (made in Italy). They have what looks like a little steering wheel (vertical axis) atop them but some other rectifiers have knobs, too. Oh, and toss in the type of lamphouse for good measure as well.

Posted by Thomas King (Member # 2745) on 11-07-2004, 10:53 AM:

It's a Cinemeccanica CX20H lamphouse. I can't find any documentation on the rectifier, nor any identifying marks. All it has is a sticker saying it passed inspection in 1995. (probably due for another one). It's a grey box, about three foot high and one foot wide. Controls are mounted on the front face as it fits just underneath the bench. Near the top, from left to right, is a small fuseholder, a non-linear scale ammeter, and a small power toggle switch. Underneath in the middle is a big black rotary knob with "increase" and an arrow marked above it. Sorry about the verbose description, but I don't have a picture of it.

Posted by Gordon McLeod (Member # 33) on 11-07-2004, 11:16 AM:

There is a possibiltiy that the rectifier can't delever the higher current safely
Have your engineer check it first

Posted by Ferdinando Innocenti (Member # 2477) on 11-07-2004, 11:27 AM:

It's important to know if your rectifier can handle this current.

But, for a better life of a lamp, you should use it at its rated values.

Ciao
Nando

Posted by Mark Gulbrandsen (Member # 72) on 11-07-2004, 05:27 PM:

You definately need to consult your rngineer!! At 50 amps you won't get the full life span out of a 2kw lamp, even at 70 amps you won't once it becomes difficult to ignite it. The bottom end of a 2kw lamp is normally 65 amps!!

Mark @ CLACO

Posted by Thomas King (Member # 2745) on 11-07-2004, 07:00 PM:

Turns out it's made by Transformers and Rectifiers Inc, a company that still seems to be going strong over here. It's capable of an output of up to 100A, so it should run alright. I'm just concerned that because there's no voltmeter in the system, I've got no way of knowing the exact power output of it. Will it automatically lower the voltage to the required 28 (or thereabouts) volts?

Posted by Randy Stankey (Member # 64) on 11-07-2004, 11:53 PM:

Virtually every xenon lamp manufacturer that I have seen packs a card or a data sheet with each lamp. It specifies what the current & voltage limits are for that model of lamp. It often includes what voltage & current that particular lamp tested at when it left the factory.

Go by what's printed on that card.

My rule of thumb is to burn a lamp at no less than 80% of its rated maximum current and no more than 100%. I strive for 90%. Often, I find that lamps burn at a current that's pretty close to what it tested at during the final Q.C. check, listed on the card.

Threfore, the lamp should probably be burning at no less than 56 amps and no more than 70. I would expect the thing to burn happily at 60-65 amps.

I agree with the others about being careful when ramping up the power supply. Once you have verified that it's safe to do so, ramp it up slowly if you can. I like to let the lamp burn for a few minutes to heat up before I make adjustments. (Assuming current & voltage are not running out of spec.) Once I make the adjustment, I let it burn for a while to see if it changes when it heats up then make alterations accordingly.

Once I have the lamp burning the way I like it I check on it every few days to see if it's settling in. Only infrequenly do I find that a lamp needs a second readjustment. 90% of the time, I find that xenon lamps burn at or near the settings you put them at until they start to get near the end of their life span.

Once lamps are settled in, any sudden changes indicate to me that there is a problem that needs to be looked at right away.

Posted by Monte L Fullmer (Member # 2797) on 11-08-2004, 12:09 AM:

Course, you can do the math, with having the bulb on, take a VOM meter and tag across the "positive" and "negative" posts on the output side of the rectifer, and see what VDC's is coming out of the rectifier. Then take this voltage reading and times it by the amperage that is posted on the meter, this will give you your wattage out of the bulb operation. 2k bulbs needs 80% plus of total wattage for maximum use. (i.e. 2000w x 80% = 1600w) 2K Osrams love to be running between 72 and 85 amps-the latter when hours on the bulb are getting high. Have you tried other brands of bulbs, like Christie, and others out there? Good luck - MLF

Posted by John Pytlak (Member # 331) on 11-08-2004, 07:53 AM:

quote: Monte L Fullmer
Course, you can do the math, with having the bulb on, take a VOM meter and tag across the "positive" and "negative" posts on the output side of the rectifer, and see what VDC's is coming out of the rectifier.

Be careful: You are measuring a "live" circuit. [Eek!]

Also, don't try to measure voltage while the lamp is igniting -- the high voltage ignition pulse could damage your meter.

Posted by Steve Kraus (Member # 476) on 11-08-2004, 08:01 AM:

Isn't the voltage just going to be whatever is needed to force X amperes through the bulb? I don't see where this is would be an independently controllable variable. The voltage is going to vary with the bulb's arc gap and its internal pressure at that moment.

Posted by Scott Norwood (Member # 30) on 11-08-2004, 08:06 AM:

Side note: are you sure that you have the right bulb for your lamphouse? I have a pair of CX-20H lamphouses (with 500w lamps) and what little documentation I have for them says that they will take a maximum bulb size of 1600w (some parts need to be changed to convert from 500w to 1600w). You might want to check this first and, if necessary, get the correct bulbs.

Posted by Ferdinando Innocenti (Member # 2477) on 11-08-2004, 09:33 AM:

Scott,
it's for the little size of the lamphouse: you can use a 2000W, but only if it's a short one (for example: osram xbo2000W/SHSC)

Ciao
Nando

Posted by Thomas King (Member # 2745) on 11-08-2004, 08:28 PM:

Many thanks for all your advice, I'm glad I didn't just start fiddling with it straight off.

Apparantly the standard CX20H lamphouse is okay with short lamps up to about 1600W, for 2000W operation apparantly it needs to be fitted with a dichroic mirror or it'll overheat. Dichoric mirrors seem to be all about seperating visible light from infared. I'm guessing a dichoric reflector for an arc lamp would let the infared through it, instead of focusing it on the film.

The engineer I spoke to said that a dichroic reflector would look "yellow-tinted", so I'll check to make sure we have one, and then ramp up the current. I'll let you know if it works okay, or get someone to tell you otherwise in the event of my death.

Posted by Randy Stankey (Member # 64) on 11-08-2004, 08:50 PM:

quote: Steve Kraus

Isn't the voltage just going to be whatever is needed to force X amperes through the bulb?

Yes. But I mention voltage out of habit. Although amperage is the more significant reading, I always keep an eye on voltage just in case something goes wrong.

Posted by Monte L Fullmer (Member # 2797) on 11-30-2004, 04:14 AM:

Thx. I knew better than to check voltage before the igniter is hitting up..blasting 30 to 50k of VDC through a VOM (even though I saw a booth operator do that...toasted his VOM very quick). Nah, I usually do the checks when the bulb is running for a good half-hour. This way the current has settled and stabilized.