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» Film-Tech Forum   » Operations   » Film Handlers' Forum   » Can Miller Inverter Welder be Used for Lamp Power Supply?

   
Author Topic: Can Miller Inverter Welder be Used for Lamp Power Supply?
Joshua Waaland
Jedi Master Film Handler

Posts: 800
From: Cleveland, Ohio
Registered: Dec 1999


 - posted 08-15-2004 11:00 PM      Profile for Joshua Waaland   Email Joshua Waaland   Send New Private Message       Edit/Delete Post 
I was recently looking through the picture warehouse and saw that there was an Imax venue that used Miller Dimension welders for the lamp power supply. The welding company I work for just sold a brand new one of these on ebay that we were not using. Not that I could have used it anyhow because it was a 3-phase machine. Although it got me thinking we just bought a new Miller 350 XMT CC/CV machine that is brand new on the market this year. It uses an inverter based technology rather than transformer based. It uses much less energy and is darn near silent compared to our old machine we just outed and less than half the size. The best part is that it can run on single phase 208 AC. It somehow recognizes what type of current it is connected to and switches accordingly. There is no need for changing jumpers everytime you need to change the current supply. This is especially nice if you need to take it home for the weekend to do some shade tree mechanics.

Anyhow my wife and I just put in an offer on a house this weekend so I can finally get started on that home theater soon. The basement has been waterproofed around the edges and the previous owners took good care of it with no cracks in the cinder blocks (the walls look new). It will be a short throw but that's okay with me. I'm not going to live there forever. I'm saving my dream theater for when we build. My dream theater has me building a large room on the back of the house using both of my projectors. I am going to have one facing into the theater and a window in the booth with another facing out the window for outdoor screenings. Sorry I got so off topic I am just excited to get this house and get started.

So back to my original question. Would it be possible to use this Miller welder to supply the dc current to the bulb or carbon arc? I don't see why not. This would only be a temporary solution as it is a very expensive machine ($4,0000+)and it is definitely cheaper to get a rectifier rather than one of these. But since I have access to one of these it would be useful until I can afford a rectifier. Let me know what you think.

Josh

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Steve Kraus
Film God

Posts: 4025
From: Chicago, IL, USA
Registered: May 2000


 - posted 08-15-2004 11:25 PM      Profile for Steve Kraus     Send New Private Message       Edit/Delete Post 
Welding supplies have been used but it seems like a lot of trouble. Both xenon and carbon arc supplies must have drooping voltage characteristics meaning the voltage must drop as the current increases. A xenon supply must also have a start voltage. If all you have is the basic supply (which granted is a higher voltage before the lamp strikes due to the voltage characteristic described above) even with the high voltage RF zaps provided by the ignitor within the lamphouse the bulb will not light unless it has this higher voltage across it. This can be provided by an extra transformer winding or even a tiny little extra transformer & a few diodes. It gets disconnected as soon as the big current starts to flow (meaning the bulb lit). Not sure how the switching supplies handle this. You also need filtration; I don't know how smooth the DC is on a welding supply. Carbon arc needs only to be smooth enought that the light doesn't pulsate and react with the shutter. Xenon should be even smoother for good bulb life. Filter capacitors also create in-rush current. Bad for xenon. A carbon arc supply on the other hand needs to be able to handle the dead short created when the carbons are touched to strike the arc. I presume that's similar to welding.

Yes, it can be done but why bother, especially if you might damage an expensive unit. It's something that is more of interest when the supply being contemplated is cheaper than a real one but that doesn't sound like the case here.

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Bill Enos
Film God

Posts: 2081
From: Richmond, Virginia, USA
Registered: Apr 2000


 - posted 08-16-2004 12:34 AM      Profile for Bill Enos   Email Bill Enos   Send New Private Message       Edit/Delete Post 
Welders usually have around 20 to 50 percent duty cycles at settings much above their lowest.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16057
From: Bountiful, Utah
Registered: Jun 99


 - posted 08-16-2004 08:01 AM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
Yes they can be used. They are quite a bit less expensive than a regular 7kw rectifier and they work very good for this purpose. I talked to Miller directly about this a few years ago and I have also seen the Imax schematic and modifications if you want to call it that. The mod is VERY simple and Imax gets very good lamp life running the Millers. Because they are so inexpensive we almost installed a set at another local venue because they had problems with the rectifiers that were supplied with the equipment. Just keep in mind that these are running lamps that are 7kw and up! A tad large for home use. Also keep in mind that most Imax theatres are only striking the lamps once a day, so the inrush is not such an issue, and the mod controls it anyway.

Mark @ CLACO

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Gordon McLeod
Film God

Posts: 9431
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 08-16-2004 11:30 AM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
The early ORC rectifers were miller welders
All that is necassary is to increase the amount of capacitance in most cases as the Miller has a very high no load voltage so it usually will charge the cap up to the range of 110volts
Because they use a saturating core design in there magnetic basedwelders the inrush is not much os an issue on there switchers I don't know The Imax ones have always been the magnetic based

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