Film-Tech Forum ARCHIVE: Welder's inverters for lamphouses?

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Posted by Matthew Taylor (Member # 2310) on 03-09-2007, 01:53 PM:

Is it possible to use welding PSU's on lamphouses? Looking at the specs of some of them, it looks like they can produce the current output required but I'm not sure whether the output would be smooth enough.

Posted by William T. Parr (Member # 677) on 03-09-2007, 02:07 PM:

Matthew, It can be and has been done. We used a Miller's Welding unit as the power supply for a 3000W Peerless Mac Arc conversion at the Centre Theatre n Corpus Christi. Works very well.

Posted by Mark Gulbrandsen (Member # 72) on 03-09-2007, 03:10 PM:

IN fact Imax uses Millers at almost all theor installations.... but.... with an extra box out in front that contains filtration and other stuff to mark the DC clean enough. Take a look at some of the Imax booth photos and you will see the Millers and Imax "box mod" that mounts in front.

Mark

Posted by Adam Martin (Member # 641) on 03-09-2007, 07:10 PM:

The box on the front of the Miller rectifiers in the Imax booths only provide easy-service-access for connections.

There is a circuit board added inside the main body behind the control panel to interface with the PLC so that there is data communication that allows for remote control, remote meter readings, and the ability to reduce power when the dowsers are closed.

Unless the theater provides some other external unit, there is no power conditioning on the GT systems. The SR system sort-of has conditioning, but it's more for providing emergency power to the control console and does not feed the rectifiers. Some theaters spend extra for an electronics-grade panel to supply the audio system.

See photos here and here.

Posted by Phil Hill (Member # 371) on 03-09-2007, 07:24 PM:

Assuming the "Standard" welding supply as implied, where does IMAX develop the boost voltage and place the Tesla coil, (and auto strike ckt) for the HV necessary to start the xenon arc?

The systems I've built for 15kW water-cooled lamps where specifically designed for the function and didn't use "arc welders"...I always thought that a bit cheesy for an otherwise good product!

Posted by Mark Gulbrandsen (Member # 72) on 03-09-2007, 07:30 PM:

Somewhere I have the schematic of what they do to to those rectifiers that was sent by an anynoumous Imax tech years ago. It does include filtration and I believe the boost circuit as well. I will try to dig it up and send it to BRad. Its pretty interesting.

Phil,
Your 15kw switching rectifier bank design ALWAYS works like a champ and never gives any problems. Lamp life with it is exactly the same as it is with the modified Millers. Price out a Miller sometime as I once did to replace a single 7kw switcher on a Megasystems machine... they are dirt cheap even with the mods you have to do to them. If you call Miller and tell them Imax they know which ones are used.

Mark

Posted by Richard Hamilton (Member # 321) on 03-09-2007, 09:23 PM:

Mark,
Was that at Jordan Commons?

I didn't do the install there, but I did replace the Strong power supply with an Irem

Rick

Posted by Phil Hill (Member # 371) on 03-09-2007, 09:35 PM:

The thing that always bothered me about an IREM is the LOUD vibration of the transformers AND the crappy HIGH DC ripple! I ALWAYS had to use isolation pads for mounting and the external choke to help eliminate the shitty ripple.

I cannot recommend them for anything other than a boat anchor.

Posted by Paul Mayer (Member # 355) on 03-09-2007, 09:43 PM:

quote: Phil Hill
I cannot recommend them for anything other than a boat anchor.

How 'bout as chocks? I'm always running out of chocks for my MD-83s these days... [Big Grin]

Posted by Phil Hill (Member # 371) on 03-09-2007, 09:51 PM:

hahahahahaha! Thanks for your comment, Paul. But I thought YOU would have said something about "shitty ripple"... you know like the wine... HA! [Wink]

Posted by Mark Gulbrandsen (Member # 72) on 03-09-2007, 10:07 PM:

quote: Richard Hamilton
Mark,
Was that at Jordan Commons?

Yea.

quote: Paul Mayer
How 'bout as chocks? I'm always running out of chocks for my MD-83s these days...

I agree with Phil... Irems are absolute crap! Paul... You could use em as chocks but your back wouod eventuially give out yankin em out from the tires with a rope attached..... [Eek!]

Posted by Tim Reed (Member # 137) on 03-09-2007, 10:14 PM:

Doesn't an "inverter" convert DC to AC?

Posted by Daryl C. W. O'Shea (Member # 1303) on 03-10-2007, 02:59 AM:

quote: Tim Reed
Doesn't an "inverter" convert DC to AC?

Yeah, that's where the Irems come in. They're sort of like a double conversion UPS.

Posted by Matthew Taylor (Member # 2310) on 03-10-2007, 03:48 AM:

So if I got an 'off the shelf' welding psu, would it need modification to run a normal ....say...1600w lamphouse?

Posted by Robert Minichino (Member # 3495) on 03-10-2007, 08:38 AM:

Assuming it was up to supplying the current you need at 100% duty cycle, you'd also need a boost supply to generate a higher voltage for striking.

Posted by Mark Gulbrandsen (Member # 72) on 03-10-2007, 09:00 AM:

A 120 volt DC 5 amp supply with a couple of thousand MF storage. This supply would be fed through a blocking diode to the output terminals. The boost supply should be relay activated to drop out when the low voltage side takes over. This can be done by a current sense arrangement that senses the heavy draw on the output. You would also need to add filtration to the welders supply... Just enough... not too much. Too much and you might exceed the inrush current spec. on the bulb, then short lamp life will ensue.

Mark

Posted by Richard Fowler (Member # 893) on 03-10-2007, 11:57 AM:

Years ago TECO and some other people where using welding rectifiers with "fair" results. Their boost design was to up the amperage lever to strike and manually lower for operation. The aluminum core of these rectifiers where not truely 100% cycle. The ripple was so awful that the bulbs lasted less than 1000 hours with major deposits on the anode / cathode. One of these conversions caught on fire in Miami. The "designer" who has an electrical engineering degree, mounted the ignitor in a plexiglas case....inside...the lamphouse over the bulb.
Millers are another story and with mods very servicable. You can use a smaller welder unit with proper filtration and make a serviceable unit for not too demanding situations. On the German version of Film-tech (www.filmvorfuehrer.de) one tech is showing his filter mod on a small welder unit....ich kann deutshen lesen [Cool]

Posted by Gordon McLeod (Member # 33) on 03-10-2007, 12:21 PM:

Some of the older ORC rectifiers are millers
the duty cycle of many smaller welders would be an issue
Lee Artoe had an interesting method of killing the boost supply that eprad also used
They had a magnetic reed switch mounted to the side of the filter choke that controled a relay on the boost supply
when the current flowed through the choke when the lamp lit the mag field opened the reed switch dropping the boost supply

Posted by Richard Fowler (Member # 893) on 03-10-2007, 01:03 PM:

I serviced many of those reed switches on Eprad units [Roll Eyes]

Posted by Mark Gulbrandsen (Member # 72) on 03-10-2007, 03:26 PM:

quote: Gordon McLeod
Lee Artoe had an interesting method of killing the boost supply that eprad also used

Lee Artoe also burned down at least one theater with his rectifier design and thats why his company sat intact and in limbo at its Belmont Street address for decades until he died a couple of years back. It was always fun to rummage through his place. There were NASA modified Jet Arcs in the basement used as solor furnaces and Ampex tube amps stacked like Chordwood at the end of a tunnel in the basement. He claimed to be the inventor of Xenon which we all know to be a false statement. He also claimed to be the first to automate a booth... actually Artoemate a booth. There were brand new Ashcraft Core Light lamphouses upstairs last time I was there in the mid to late 90's. He was also a slum landlord and ex-Chicago Bears running back... he went through multiple hip replacements over several decades. He was ALWAYS cranky [Mad]

because his hips bothered him so much !
Lee Artoe Article

If you look at the Miller specs they are also not rated for continous duty. The Miller man told me they just use one thats alot larger than is needed.

Mark

Posted by Gordon McLeod (Member # 33) on 03-10-2007, 03:32 PM:

The duty cycle is usually inversley proportonal to the output current

Posted by Matthew Bailey (Member # 601) on 03-10-2007, 08:28 PM:

I'm wondering if you want to use the booth's existng motor-generator to operate a xenon lamp how do you do it? I was in a theatre several years ago that was vacant but stll had power to it. It had three Simplex Aeromatic platters & some Simplex,Century & Brenkert stuff (BX 80 head I believe) stripped,dismantled & lying around the booth,but I believe from the way it looked was the the original motor-generator which I started to my surprise it still had power to it,which was being used to operate one or more xenon lamps. The theatre was taken down for a parking lot.

Posted by Richard Fowler (Member # 893) on 03-10-2007, 11:57 PM:

Kneisley at one time made a ballast kit so you could use a motor generator set.
Lee Artoe....he was a character [Cool]

The last time, in the early 1970's, he took me to O' hare airport in a snow storm and we ran off the road a few times [uhoh]

I fixed a load of his lamphouses which had major ventilation problems. I bought a few of his Artoe mation projectors, which where Prevost P-70's, for several special venue jobs.

Posted by Robert Minichino (Member # 3495) on 03-11-2007, 12:02 AM:

As most MG setups I've seen use ballast resistors to limit the lamp current, if the open-circuit voltage is sufficient you should be able to connect the Xenon lamphouse just like a carbon arc (adjusting the rheostat for the correct running current, etc.). It would certainly be an interesting marriage of old and new. [Smile]

Posted by Gordon McLeod (Member # 33) on 03-11-2007, 08:48 AM:

Atlantic Audio Visual ran there first north american xenon systems with zies lamphouses off MG sets
Xetron also made a convertor box for MG sets as well

Posted by Louis Bornwasser (Member # 3063) on 03-11-2007, 09:42 AM:

The Memphian Theatre in 1979 (Memphis TN....Elvis' favorite!) had Magnarcs converted with an early Christie conversion. Used a MG with small ballasts. The ballasts looked like very small rectifiers that sat on the floor near the lamphouse; weight: 10 lb or less. Other than no light and high power cost; it seemed to work well enough. Louis

Posted by Gordon McLeod (Member # 33) on 03-11-2007, 01:18 PM:

Lamps lasted for ever probably because of the usually 12phase output of many of the big hertners and their high impedance

Posted by Matthew Taylor (Member # 2310) on 04-29-2007, 02:58 PM:

Is there anywhere I can get a schematic of the sort of filter and booster circuit needed for a 1600-2000W inverter?

I'm quite capable at putting together circuits but not so good at design, so I could do with some direction.