Film-Tech Forum ARCHIVE: Zeiss arc lamps

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Posted by David Hayward (Member # 9692) on 12-04-2017, 12:31 AM:

Hi...Yesterday I picked up a pair of Zeiss carbon arc projector lamps that were removed from a local cinema. Thay have both been converted to Xenon short arc bulbs, which are in tact and look good.The internal workings for initial striking of the arc are complete, presumably from the old carbon system, but no rectifier or D.C power supply to keep them lit. I have very little electrical experience of these systems, and, given the price of the bulbs, and their inherent hazardous nature, I am seeking help before I do anything.... I have heard they can be run using an invertor arc welder, but not sure. Can anyone help me with wiring diagrams, or info please...? I can post photo's of what I have, if that helps. Thankyou, David.

Posted by Dave Macaulay (Member # 813) on 12-04-2017, 05:10 AM:

A carbon arc strikes by having the carbons touched together momentarily and then pulled apart to the correct gap. Then they need to be fed towards each other at just the right speed to make up for the rate of burning, plus keeping the gap at the mirror focus. That mechanism will not work, at all, for a xenon lamp. Some of the original carbon adjustments are likely used to position the xenon lamp for optimising image brightness. The feed motors are not used. A carbon arc mirror is not well suited to xenon lamps. Conversions involved essentially gutting the lamphouse and putting in a new mirror, ignitor, and wiring.
A lamphouse power supply- "rectifier" - is something like a welding unit but not exactly. DC welders may not have enough filtering to avoid lamp flickering - since this flickering is unlikely to be exactly at the film flicker shutter frequency, a lamp that seems dead steady because we can't see flicker above 30 Hz or so can cause severe slow flickering on the image.
You need a high voltage AC ignitor to start a xenon lamp (10,000V+?). That is probably the "internal workings for initial striking of the arc" you see. These ignitors may be manual (push a button to start the lamp) or automatic. Auto strike senses the DC voltage from the power supply, if that's too high for the lamp to be on then it tries to strike. Welding units want to have low open circuit voltage, mainly because 100VDC+ tends to electrocute welders... so if you get a welder that makes clean enough DC power it isn't likely to trigger autostrike.
There's more to it like inrush capacitance required and current regulation but basically a welder makes a poor lamp supply. Imax 15/70 projector xenon lamp power supplies for 12kW and up were modified large Miller DC welding machines.
With many obsolete (unfortunate word but is there a better one?) film projection systems just sitting in projection rooms (because the cost of having them carried out to scrap is more than the scrap value...) there must be actual xenon lamp power supplies available to you. They do show up online but shipping will hurt: newer switching type supplies are relatively light but the old "brute force" models are fricking heavy.

Posted by David Hayward (Member # 9692) on 12-04-2017, 10:15 AM:

Thanks for the info Dave...
Given the fact that I only intend using the projector in a home cinema environment, and the relatively complex and hazardous nature of the arc system for the lamp, I am now considering gutting the internals, and using a 2000 watt halogen theatrical spot lamp bulb in its' place. Given the short projection distance needed, hopefully this may provide enough light using the original mirror still fitted in the lamp. I have two arc lamps anyway, so one will remain as is, if I can sort out the right power source etc.....?...