Projector SO CLOSE to being setup!

[Josh Jones]

The biggest challenge is getting bulbs now. You can find chinese ones on ebay, but the reflectors now are pretty rare and very expensive to have replaced if you could even find one. All the modern bulbs are made for DLP machines, and appropriate adapters would need to be made to fit these modern bulbs in an old lamphouse. All the lamps and rectifiers I pulled out of a decommissioned theater were 1600's but I left the bulbs behind. The rationale was I had to go through every machine in the building to find two reflectors that weren't already destroyed by an explosion. Towards the end of film, no one was spending money on bulbs, and was trying to make it to the finish line without buying more supplies.

The datasheet for any bulb will show what its current range is. Most bulbs will go down to 60% of rated current and still run OK. Depending on the age of the bulb, the arc can get unstable and frequently go out if your down too far. Your 2500's may go down to 1200W or so, which would be bright, but you could always defocus the lamp a little.

As far as the rectifier, you could try and retap the transformer for higher voltage and see what you get on single phase. All the transformer supplies I've seen control bulb current by controlling output voltage. The gap in the bulb has a certain amount of resistance, and raising the voltage across the gap also raises the current, and vice versa. On these strong rectifiers I have, I ran them on 120V (they are 240V nominal) and was able to run a 500W lamp without issue. Its still pretty inefficient compared to a switcher (Even the Strongs pulled over 1KVA to make 500W of light). The 500W switching rectifier I built pulls 650W out of the wall to make 500W, and has PFC for unity power factor.

Josh

[Walt Shires]

Other than the physical size of the bulbs from China (new ones) if they are for the big DLP projectors - is there something that would prevent you from using it in a 35mm lamphouse? I can make an adapter easily that would bring the arc to the right position so I'm not too worried about that. If it is OK and the problem is just a form factor thing, then that might be a good route to go to get a 1000w bulb and then I can work with the rectifier I have and see if I can get the voltage correct for it all to work.

On the bulb exploding... when the bulbs get near their end of life - do they tend to explode? And then take out the mirrors? If so -what is the alternative?

On occasion, while looking at eBay, I see something that is referred to as an arc lamp for a projector that is in like a cage with a mirror - I'm assuming it's a module that is meant to go into a digital projector. Is that going to be the next thing we all have to try to get up and running?

BUT..... building a new switching rectifier..? I would love to hear more about that... if you have the time!

[Josh Jones]

The bulb datasheets specify the physical dimensions of the bulbs. As long as you can get the arc center at the correct location in the aperture of the reflector, all is good. I believe Brad has modified his SLC consoles for DLP bulbs, as toward the end of the film era, Christie was making adapters for their legacy consoles and lamps to accept DLP bulbs. If you have access to a lathe, there is no reason you can't make an adapter to use newer bulbs.

As the lamps age, tungsten boils off the electrodes and sticks the the quartz envelope. This raises the temperature of the glass, and after many heat/cool cycles, the glass gets more brittle. This is why most folks replace their lamps either at warranty, or when the bulb begins to flicker, become hard to start, etc. With an old Christie lamp like yours with dichloric glass, replacements would likely be very hard to find. My advice would be to tread carefully.

The xenon lamp modules were made for a variety of uses, but many of them were made for smaller DLP projectors, up to 1KW I believe.

The supply I built works a little differently from a conventional rectifier. I used an COTS (commercial off the shelf) supply with constant current programming. I picked a supply that would produce the current I needed and was close to the voltage the lamp wants. This power supply feeds the lamp through blocking diodes to keep the boost supply out of it. The boost supply is a conventional full wave supply designed to develop about 90 volts at a few hundred milliamps. This charges the power supply output capacitor to allow the bulb to strike. Once it does, the voltage across the lamp collapses and the constant current supply takes over to run the lamp at steady state. Without the boost supply, the lamp won't strike on its own. With a 500W Osram lamp, my lamp will strike on the first try whenever the supply is over 40VDC. I have attached the schematic for my supply.

I'm far from an expert in these things, but have been around for a while. I welcome useful knowledge and criticism for the good of the knowledge base here.

Josh

[Ryan Gallagher]

but the reflectors now are pretty rare and very expensive to have replaced if you could even find one..

Feeling pretty lucky I just scored two NOS Strong Super Lume reflectors (metal not glass) at a cheap price. We have two backups but they are both used and quite pitted already. Now the backups are 2nd tier backups

[Tony Bandiera Jr]

Hi Josh,

It looks like you've already done exactly what I was going to try - complete with the bare bones power supply. Heck... probably the same ebay seller! I had *some* hopes it might work because the headlamp bulb thing did project a decent image... it's just not bright enough.

Another member here (Ryan) said he used one of the calculators and came up with 575 w needed for my screen (it's a 180" in a fully light controlled theater room. we just built) I remember that the bulb I had when it was working was SUPER bright on the small screen I had in my garage at the time and it's a 2500. My simple brain wonders if 1000 is a better number because it for sure won't be too dim. or if a 575 would actually be fine. I would like it to be properly bright.... but, I'm just a home theater person and planning on watching trailers and probably only do feature lengths for "special events"

I had read a few articles about people who took a 3 phase rectifier and only ran 2 phases to it and it basically just put out less power. I do have the schematic for the rectifier I have... and although I didn't get it running the last time I tried I was going to replace all the capacitors and try again. There is one big one and a handful of disc caps so that will be easy. On that line of thought though.... I don't know how xenon bulbs work. If they are less wattage... do they still run a 30V DC and it's just lower amperage? Or are the both lower amperage AND lower voltage?

Anyway - I would LOVE some help/advice/ideas and appreciate it all! Tell me what you think might be a good approach... or if just using a different rectifier would be the better thing to do. I'm up for any of it.

Walt, welcome to the forum! As you have seen there are a lot of good folks on here and you'll learn a lot. Be sure to also check out the old forums (Forum Archive) for more posts on this subject.

My advice? Get rid of that Christie rectifier. They are basically junk and have a history of going up in flames (tap switches in particular). The amount of current you'd need to single phase that one is considerable and will further stress that marginal tap switch. You'd waste a lot of time and money recapping it for an uncertain (and unsafe) outcome. (That rectifier is based on a slightly modified welder supply that should only be run on a 20-30% duty cycle.)

There are many sources for those newer Strong switchers which will not only operate safely on single phase, but will use a LOT less electricity and be tons safer.

Again I lament the passing of John E, as he had several of those Strong Switchers (including one I gave him in exchange for stuff I needed) that he would have cut you a sweet deal on.

[Josh Jones]

Feeling pretty lucky I just scored two NOS Strong Super Lume reflectors (metal not glass) at a cheap price. We have two backups but they are both used and quite pitted already. Now the backups are 2nd tier backups

Optiform made the original reflectors for strong an likely still has the form to make those.

There are many sources for those newer Strong switchers which will not only operate safely on single phase, but will use a LOT less electricity and be tons safer.

Under 2KW building a lamp supply isn't that hard. Even the solid state rectifiers Strong made had pretty lousy power factor.

Josh

[Walt Shires]

OK... I will heed ya'lls advice on the Christie Rectifier and just leave it alone or maybe use the cabinet when making something else. I'm hoping the lamphouse is considered OK? At least as far as safety is concerned?

Just for my understanding of how these bulbs work I have a question about boost supply part. The christie lamphouse I have has a shoebox sized area that is marked "Danger High Voltage" on it. There is a button on it for Lamp Start. I had assumed that the lamphouse provided the high voltage to start the lamp, and then the main DC power from the rectifier kept it going. I understand now that the Rectifiers also start out at a higher voltage (the one I have said 100V I believe) and then when the lamp strikes it goes down to a normal "operating" voltage (28-36 V DC). I'm also assuming that the lamphouse has some kind of very high voltage circuit that really helps jump the gap in the bulb - like a 10,000 volt type circuit and when you hit the button it puts that voltage to the lines to the bulb. Or am I wrong about that? Or is it they all work differently with various methods of starting the lamps?

On the rectifier... is there some kind of logical circuit involved in switching the power from a lower amperage 90V DC to a high amperage 28ish V DC? Or - is it simpler... that a capacitor on the output lines charges and can supply the higher voltage... but once that voltage is used up out of the capacitor the bulb just use up so much power that the capacitor never really charges up again to that higher voltage? I think my question is - is the 28V DC and the 90V DC (via a capacitor) all on the same copper wires? Or is there some switching involved that gets triggered and alters the circuit?

I'm gonna look at Josh's schematic and try to understand it - I think building a power supply would be a good project. This is also supposed to be fun! I would also be happy to acquire a Strong Rectifier - if anyone has one to part with. I plan on teaching all my kids about it and how it all works. They seem to like all this old stuff and we all go to antique stores all the time. Not that these are antiques (yet) but it's good to keep it all going in my opinion. I think there is a lot of knowledge to be gained by "old stuff."

Incidentally, we just picked up a Jukebox for the "Lobby" of our home theater. It's a 1972 Rowe AMI SMM6 "Superstar" I have it sort of working... mostly by reseating all the connectors and cleaning some of the circuit board traces and the copper "brushes" it uses on those boards. Right now it will only play the "B" sides to the 45's. I was able to figure out that the solenoid that moves the trigger pins for the "A" sides isn't firing.

To me, it's truly fascinating how some of these older machines work. Such ingenious ideas about how to do things. For those who didn't know, this jukebox uses a circular series of pins that represent the records. There is an outer ring and an inner ring. The outer ring pins represent the A sides and the Inner ring are the B sides. So, while a record is playing there is a mechanism that will push out the pins based on the selection you made. Every time you make a selection a pin is pushed out. Then, the player mechanism will spin around and when it hits a pin it will then play that record and push the pin back the other way to reset it. This is how they made the machine able to que up selections that the customer made as they stood at the machine while the first song was playing. Here is a photo of it:

IMG_4787.jpg

[Josh Jones]

The box in the lamphouse inline with the bulb is the igniter. It is a small tesla coil that produces a high RF voltage that breaks down and ionizes the gas in the gap of the bulb. Because it is an AC RF pulse, sufficient bypassing is required to protect the blocking and rectifier diodes. Sometimes a fair amount of EMI mitigation is required to prevent the RF getting into places you don't want. Once the gas is ionized, the boost supply voltage starts to flow through one of the plasma filaments in the gas and starts the current flow. The boost current is several times that of normal operation, and serves to grow the width of the plasma channel to the point that normal operation can commence.

Most modern rectifiers have a separate boost circuit and blocking diodes to generate the higher voltage. Some small supplies, like my old Kniesley supply, had sufficient 'reactance' (read: poor regulation) that open circuit voltage was sufficient to allow bulb ignition. Under load, the voltage would collapse to normal operating voltage.

Josh