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Old 05-10-2013, 11:37 PM   #1
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Options for powering DC Xenon lamphouse...


Hi all,

I've recently acquired an older 35mm projector and Christie Xenon lamphouse from a theater that's converting, and will make an attempt to get it working. The Xenon lamphouse uses high-pressure Xenon bulbs (Christie Xenolite CXL-10) which are rated 20VDC, 45A.

The lamphouse comes with a lovely, very heavy and VERY OLD silicon rectifier unit which has 3-phase input. My guess is that it is only a few years removed from the selenium days.

I would like to run this from a single phase source.

I can think of 3 options --

1. New DC power supply -- I can probably find something much, much lighter that would work sufficiently. The lamphouse is simple -- DC+, DC-, and 120V AC inputs for the bulb striker, along with 2 remote control inputs, so nothing too complex is necessary.

2. Electronic phase converter to use with the old PS -- has anyone used an electronic converter with a DC rectifier? Do they work? What would I need for a 1 kW 3-phase load?

3. Rotary phase converter -- very expensive, my last option, but may be the only way.

Any thoughts for me?


Last edited by flasherz; 05-10-2013 at 11:40 PM.
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Old 05-11-2013, 01:22 AM   #2
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Options for powering DC Xenon lamphouse...


Building your own power supply would be somewhat difficult.

Xenon lamps need pretty stable DC or they flicker a lot. Plus, they need pretty high voltage to strike the initial arc, and you need to protect the high current DC circuitry from the strike voltage.

Be careful with the lamp. It's under about 80PSI when cold, more when it's hot. And they're expensive. If you touch it with bare skin, the slight amount of oil you leave behind will very likely make it explode when it reaches operating temperature.

The older power supplies were pretty much bullet-proof, the older ones with variable current via traics or SCRs were prone to failure.

As bad as it sounds, a rotary phase converter may well be the best option. I doubt if a VFD would work, as the load starts out pretty much zero then suddenly goes up when the lamp strikes. The VFD would likely see the sudden current increase as a fault, and when the lamp is switched off, it could easily burn up the output transistors.

Rob

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Old 05-11-2013, 02:25 AM   #3
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Options for powering DC Xenon lamphouse...


Those xenon arc lamps are serious explosion hazards, and serious shortwave UV hazards. They are no joke. I have worked with them. Read up in detail on proper handling and operation. There are two important electrical considerations for powering those lamps: First, they need a regulated constant current supply, not constant voltage. The lamp has negative resistance (or near-zero resistance) in operation, so voltage is the dependent variable and current must be controlled. Second, the starter must impose about 20,000V across the lamp to initiate the arc. The series-injection starter must have a safe return path for the high voltage RF starting pulse, other than through the lamp's high current supply. Otherwise the starter will fry the power supply's output section. It just so happens that the operating characteristics of these arc lamps are pretty similar to the characteristics of a welding arc. I have it on good authority that some projection lamps have been operated using welding power supplies in commercial use - specifically in IMAX projectors. That information is on the internet somewhere, in Usenet archives. 45A at 20VDC constant current sounds a lot like a small arc welder. Since the lamp needs to run continuously, the welder needs to be oversized substantially compared to the operating current of the lamp. Harbor Freight sells this nice little inverter welder which would probably do the job: http://www.harborfreight.com/welding...der-91110.html I have one, and use it for both welding and also other electronics applications. Now, there's the problem of the starting pulse. You'll need to place a low impedance capacitor across the output of the welder to pass the high-frequency starting pulse and avoid blasting the output section of the inverter with high voltage RF. I would probably use a bunch of ceramic disc caps in parallel. The exact value is not critical, but it's important that the capacitors be as close to the lamp as possible (but obviously before the starting pulse injector), and connected with short leads.
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Old 05-11-2013, 04:16 AM   #4
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Options for powering DC Xenon lamphouse...


Thanks for the input.

I am aware of the explosion (and other) hazards, as I'm a former carbon-arc and Xenon 35mm projectionist (from the days when being a projectionist meant something, not today's push-the-button-and-then-go-tend-to-the-concession-stand operators). Being familiar, I have my long sleeve coat, gloves, and full facemask that I use when handling the bulbs. So I'm familiar with the safety aspects... just not so much with how to handle powering them using single-phase.

I'll look into the welder. mpoulton, when you talk of a "bunch" of disc caps, how many are you thinking? 10? 100? And do they need to be rated for the high voltage starting pulse, or just for the main supply?

I will have to look to see if they have already built this into the lamphouse -- these caps could easily be connected across the two terminals in the lamphouse itself.

If I went the rotary phase converter route, what size would I need for 1 kW? Is it just a straight conversion from 745W / HP, so that a 3 HP converter would work, or do I need more?

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Old 05-11-2013, 11:31 AM   #5
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Options for powering DC Xenon lamphouse...


The capacitors do not need to be rated for high voltage, because they must have a low enough impedance at RF (100kHz or so) to pass the starting pulse without developing more than a few tens of volts across them - otherwise the inverter will be damaged. There is a good chance that bypass caps are already in the lamphouse, since that's where they should be located. If I were going to add them, I would probably use something like ten 0.1uF caps in parallel. That would have 1.6 ohm impedance at 100kHz, which should be low enough to pass the starting pulse without causing a problem.

If you keep the existing power supply, the rotary phase converter should probably be over-rated by a little bit to ensure stable voltage on the generated leg. Maybe a 2HP converter for a 1HP (0.75kW) load.
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Old 05-11-2013, 11:45 AM   #6
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Options for powering DC Xenon lamphouse...


The power factor on a Xenon rectifier is about 30 - 50%. Seriously, it's that low.

To size a rotary phase converter, look at the 3 input amps and upsize it a bit.
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Old 05-11-2013, 11:56 PM   #7
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Quote:
Originally Posted by mpoulton View Post
Harbor Freight sells this nice little inverter welder which would probably do the job: http://www.harborfreight.com/welding...der-91110.html I have one, and use it for both welding and also other electronics applications.
Is that a DC power supply? I was poking through the manual and the parts list seems to show a transformer but doesn't give a clue that there is a rectifier in there.
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Old 05-12-2013, 12:36 AM   #8
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Options for powering DC Xenon lamphouse...


Quote:
Originally Posted by flasherz View Post
Is that a DC power supply? I was poking through the manual and the parts list seems to show a transformer but doesn't give a clue that there is a rectifier in there.
It is an inverter welder (switching power supply). They are all DC, except the really fancy ones which are AC/DC. It's got + and - marked on the front...
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Old 05-12-2013, 12:39 AM   #9
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Options for powering DC Xenon lamphouse...


The other important item is when you hook up the DC supply to the xenon arc lamp(s) is watch the portarly to make sure you have correct postion for electrode due one will be + and other end will be - so do not try to run in reverse mode otherwise you will burn them out quick.

Merci,
Marc
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Old 05-12-2013, 06:05 PM   #10
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20V at 45A thats only 900W !
1000w Transformers are readily available.
A simple transformer, bridge rectifier, and filter caps
will easily do this job !
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Old 05-12-2013, 07:27 PM   #11
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20V at 45A thats only 900W !
1000w Transformers are readily available.
A simple transformer, bridge rectifier, and filter caps
will easily do this job !
These lamps need to have their current adjusted occasionally. usually up as they age.

They also need to have very little ripple on the DC. Every rectifier I've worked on has a choke in addition to the filter caps, and usually the transformer has multiple taps that can be easily changed. Or some sort of electronic current regulation.
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Old 05-12-2013, 09:26 PM   #12
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Options for powering DC Xenon lamphouse...


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20V at 45A thats only 900W !
1000w Transformers are readily available.
A simple transformer, bridge rectifier, and filter caps
will easily do this job !
Absolutely not! These lamps require a regulated constant current source.
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Old 05-12-2013, 09:27 PM   #13
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These lamps need to have their current adjusted occasionally. usually up as they age.

They also need to have very little ripple on the DC. Every rectifier I've worked on has a choke in addition to the filter caps, and usually the transformer has multiple taps that can be easily changed. Or some sort of electronic current regulation.
And almost certainly a magnetically gapped or shunted transformer core, for current regulation.
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Old 05-13-2013, 11:40 AM   #14
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Options for powering DC Xenon lamphouse...


I think I'll go the small welder route - seems like a reasonable investment. I have several spare bulbs in case one of them suffers a failure due to a power supply problem. I always have the old power supply and can go to a rotary converter if I have to.

New very high-quality power supplies tend to run about $1,500-3,000 for Xenon lamps, including igniter. That's a bit out of my budget range (this is more of a hobbyist project).

I really appreciate all the input, especially mpoulton's!
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Old 05-13-2013, 01:30 PM   #15
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Please post your results! I'm very interested in how this works out. I have a couple of these lamps in storage that I played with a few years ago, but never really used for anything. I built a series injection igniter and got them to strike using a huge 48V DC power supply with a spool of wire for ballast resistance to limit current, but this was nothing more than a test setup and I never tried to make it work well. If you have good results, I may hook up my welder and build a xenon arc spotlight.

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