This is topic Stupid, Basic Xenon Question in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Jeff Taylor (Member # 443) on 04-23-2001, 09:49 AM:
Sorry if this has been discussed before. I find that my xenon amperage tends to drop 10%-15% as the lamp and reactance power supply reach full operating temperature. There's no noticeable change in light output, so I'm curious if the lamps become more efficient and draw less amerage as they get hotter and stabilize, is it just that I don't notice the light output drop, or is it some other explanation. Thanks for any info.
Posted by Darryl Spicer (Member # 711) on 04-23-2001, 10:35 AM:
actually it is the current stablizing or gradually increasing that causes this. This is normal. When your bulb starts the current pegs out at around 120volts then the igniter kicks in using this full voltage. When this happens it will drop the voltage belowe the normal opperating voltage causing the amperage to be high. Once the voltage stablizes the amperage will decrease.
Posted by Jeff Taylor (Member # 443) on 04-23-2001, 01:27 PM:
Thanks, Darryl!
Posted by Josh Jones (Member # 447) on 04-23-2001, 11:54 PM:
Is that also why rectifiers quiet down after a few minutes of operation?Josh
Posted by Randy Stankey (Member # 64) on 04-24-2001, 12:30 AM:
I'd say that and the fact that they heat up causing the parts of the transformer to expand, thus eliminating vibration because the parts are being "pressed together" more tightly.
Posted by Paul G. Thompson (Member # 655) on 04-24-2001, 06:36 PM:
I agree with Randy. The IREM power supplies, the ORC RPS series, and some Strongs really like to "Sing".....The more powerful IREMS can be really bad. Their current output is adjusted by a hand wheel which fools the power transformer by changing the transformer's reluctance (an opposition to the magnetic flux field).
It works like a Saturable Core Reactor. Shove an iron slug into the transformer, and the output will increase. Pull the iron slug out, and the output decreases.
Some of the old ORC RPS power supplies use a DC voltage on a separate control winding which will either pulls the core out of saturation, or increases the core saturation, thereby controlling the output.
In any event, the laminations are the cause of most of the obnoxious hum. IREM's do have small adjustment slugs to reduce the hum.
Some power supplies can be "shut up" by driving non-conductive shims such as bakelite or wood between the coil and the transformer core. The real old RPS-2500 ORC power supplies had that as standard equipment. After years of service, the shims fall out, or squash enough so they won't keep the laminations from vibrating.
Posted by John Walsh (Member # 168) on 04-24-2001, 09:09 PM:
IREM rectifier laminations can be "tightened." There are screws that (when tightened) press against small brass plates, which compress the laminations. While there is some trial and error, it can reduce the hum noise quite a bit.I'm sure other rectifiers have something to reduce the noise, but this is all I've ever seen.
Posted by Paul G. Thompson (Member # 655) on 04-24-2001, 09:25 PM:
John, you are right about the trial and error. Then you run into some of those IREM's where they were tightened so tight they stripped out or broke. ARG!The IREM Power Supplies are the only ones I saw using that technique.
Posted by Gordon McLeod (Member # 33) on 04-24-2001, 09:38 PM:
I once ordered a silencing kit from Kniesley for a old 600volt selinium xenon supply and god a box of finishing nails and a mallet in the post with instructions to hammer them into the core
Needless to say with 600 vac primary I decided the projectionist could live with the noise 
Posted by Paul G. Thompson (Member # 655) on 04-24-2001, 09:41 PM:
Gordon, I can understand why. A mallot or hammer was originally employed as a weapon of war, the hammer nowadays is used as a kind of divining rod to locate an extremely expensive part or component not far from the object we are trying to hit. 