Film-Tech Forum ARCHIVE: bulb degradation/ arc wander issue

This is topic bulb degradation/ arc wander issue in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=011437

Posted by Craig Mueller (Member # 4912) on 05-03-2013, 05:45 PM:

I'm trying to solve an ongoing (and worsening) issue where arc wander develops within the first couple hundred hours of a lamp's life and the anode and cathode are getting deteriorated in one of my screens. The set up is a christie d40 lamphouse and a christie cxl-30 lamp powered by a irem n3-150. All the diodes are fine, the power into the supply is fine (legs are balanced) however today I tested the capacitors and found that one of the 5600 uF caps was reading around 5300, and the other approximately 4800. Would capacitance readings like that cause rapid degradation of the bulb or is that close enough to spec? And if so what else could be causing the problem? I am running short on ideas, and haven't been able to source replacement capacitors in the event it is them. Thanks in advance for anyone that might be able to lead me to a solution!

Posted by Gordon McLeod (Member # 33) on 05-03-2013, 05:52 PM:

I would check the stablizing magnet and also measure the insrush current which will require a peak hold current meter and bridge
Also excessive airflow will cause unstable arc

Posted by Sam D. Chavez (Member # 1841) on 05-03-2013, 06:23 PM:

The Irem are known for very high ripple content that is hard on the bulb.

The caps are well within tolerance of these type of caps.

What did you use to measure the value of capacitance? I can't remember the last time I heard of someone actually measuring the value.

Posted by Craig Mueller (Member # 4912) on 05-03-2013, 06:46 PM:

I measured the capacitance with a cheapo capacitor tester/ EFR bought online. I've been trying to scratch things off the list of possibilities I've read on here so it seemed worth the 25 bucks. Adjusting the magnet doesn't seem to have any effect on the stability and bulbs start out their life stable but degrade over the first few hundred hours to a candle in a storm.

Posted by Gordon McLeod (Member # 33) on 05-03-2013, 08:30 PM:

typically we always got long bulb life with irems