Anyone else have issues with their Lowel Omni lights? - Page 4 at DVinfo.net

Go Back   DV Info Net > The Tools of DV and HD Production > Photon Management

Photon Management
Shine an ever-loving light on you.


Reply
 
Thread Tools Search this Thread
Old February 29th, 2008, 06:18 PM   #46
Inner Circle
 
Join Date: Feb 2007
Location: Tucson AZ
Posts: 2,207
Mike,

What kind of voltmeter do you have, digital or analog with a needle?

Either way I don't think this is a situation requiring great precision - just crank it down until the bulb looks a little less bright. May not be perfect, but you should be better off
Jim Andrada is offline   Reply With Quote
Old February 29th, 2008, 06:26 PM   #47
Major Player
 
Join Date: May 2006
Location: Toronto ON Canada
Posts: 731
Quote:
Originally Posted by Jim Andrada View Post
What kind of voltmeter do you have, digital or analog with a needle?
Analog w/ needle.

Quote:
Originally Posted by Jim Andrada View Post
Either way I don't think this is a situation requiring great precision - just crank it down until the bulb looks a little less bright. May not be perfect, but you should be better off
I don't know... I the kind of guy that aims for precision as much as humanly possible (must have inherited that from my grandfather, a precision optics maker during WWII). There must be a way to scientifically measure and quantify the change that is occurring.
__________________
Mike Barber
"I'm laughing to stop myself from screaming."
Mike Barber is offline   Reply With Quote
Old March 1st, 2008, 12:49 AM   #48
Inner Circle
 
Join Date: Feb 2007
Location: Tucson AZ
Posts: 2,207
Mike,

I feel for you - I'm the same way.

I'm really puzzled about why the meter isn't showing a voltage drop. If it were digital I could at least invent some plausible (albeit probably wrong) explanation, but old fashioned voltmeters should show the difference I think.

Hmmm.

Just a thought, but does the needle flick back and forth a bit at what seems close to a consistent 60 Hz? Does it show 0 when the dimmer is at minimum setting?

What brand is the dimmer? I'll go to the store in the morning and get one and try to duplicate what you're seeing.

Re how to calibrate:

There are several ways to do it, but not sure you'd have the appropriate equipment.

You could try to catch the difference in color temperature - if the lamp is really running at overvoltage it should have a slightly higher than rated color temperature. Problem is that the difference would be pretty small and the rating is probably only nominal to start with so there would be lamp to lamp variations.

A good exposure meter might catcht the difference, but again we're only talking about a pretty small variation from standard, so the precision/repeatability of the test equipment and test setup would be a big unkown.
Jim Andrada is offline   Reply With Quote
Old March 2nd, 2008, 04:12 PM   #49
Major Player
 
Join Date: May 2006
Location: Toronto ON Canada
Posts: 731
Quote:
Originally Posted by Jim Andrada View Post
Just a thought, but does the needle flick back and forth a bit at what seems close to a consistent 60 Hz? Does it show 0 when the dimmer is at minimum setting?
All along the dimmer's range, it stays constant. The only time it drops to zero is when I click it to the "off" position.

Quote:
Originally Posted by Jim Andrada View Post
What brand is the dimmer? I'll go to the store in the morning and get one and try to duplicate what you're seeing.
Thank you, but I wouldn't want you to waste your money! What I bought was a Leviton "Decora Sureslide" slide dimmer (part# 6621-W). It's single pole, rated for 600w. It ran me significantly more than the rotating knob dimmers, but I liked the sliders for their control (and I intended to be able to tape a stopping point to make sure I didn't accidentally go over my 117v point... I'm all about those little details). It ran me about $20 CAN each.

I ordered some DYS 600 watt lamps that are rated for 126v, which I hope will get me by. :-/
__________________
Mike Barber
"I'm laughing to stop myself from screaming."
Mike Barber is offline   Reply With Quote
Old March 2nd, 2008, 06:58 PM   #50
Inner Circle
 
Join Date: Feb 2007
Location: Tucson AZ
Posts: 2,207
Hi Mike,

No problem. Now you've got me really curious about what is going on here. I bought a rotary dimmer and I'm going to set up an experiment as follows:

Wire the dimmer into the line with a lamp socket also wired in, and attach the voltmeter as well.

Then I can confirm if the dimmer is dimming the bulb and also showing lower voltage. If the bulb dims and the voltage doesn't shift, then I have a couple of other ideas of what is actually going on that I can follow up on.

Maybe I'll also get a slide dimmer - depends on the outcome of the first set of experiments.
Jim Andrada is offline   Reply With Quote
Old March 3rd, 2008, 02:41 AM   #51
Inner Circle
 
Join Date: Feb 2007
Location: Tucson AZ
Posts: 2,207
Mike,

OK - I think I know what's going on.

I hooked up a bulb and a dimmer. The bulb was in a fixture with a separate on/off switch.

When I switched the bulb on and then checked the voltage at the base of the fixture, it dropped as the bulb dimmed. Exactly what one would expect.

But when I switched the bulb off, and checked the voltage at the base of the fixture, the voltmeter dropped slightly, but not much as I turned the voltage down.

Put the bulb in the circuit and you get what you'd expect, take the bulb out of the circuit and you get pretty much what you've described.

In other words, because of the way these dimmers work (ie not really reducing the peak voltage, just cutting off the current for an instant every cycle), you can't just measure the voltage without sufficient load in the circuit. Hook up a bulb and your voltmeter should be able to see the "effective" voltage flowing through the circuit and you ought to be able to match it to 115 or whatever pretty closely.

I think you're in good shape after all.

Hope this helps. I was kind of suspecting this, but it was fun to actually see it happen.
Jim Andrada is offline   Reply With Quote
Old March 3rd, 2008, 02:33 PM   #52
Major Player
 
Join Date: May 2006
Location: Toronto ON Canada
Posts: 731
Quote:
Originally Posted by Jim Andrada View Post
Hook up a bulb and your voltmeter should be able to see the "effective" voltage flowing through the circuit and you ought to be able to match it to 115 or whatever pretty closely.
I'm not sure I follow... how would measure with a voltmeter if I have a fixture plugged in to the dimmer?

BTW... Jim, you're awesome! I can't possibly express enough my gratitude for your help!
__________________
Mike Barber
"I'm laughing to stop myself from screaming."
Mike Barber is offline   Reply With Quote
Old March 3rd, 2008, 03:58 PM   #53
Inner Circle
 
Join Date: Feb 2007
Location: Tucson AZ
Posts: 2,207
Well, the easiest way would probably be to use a reasonably sturdy extension cord with a double or triple outlet on the end and plug the lighting unit into it and stick the voltmeter probes into one of the unused outlets.

I just used a standard household fixture and left the wires bare on the botom so I could get the meter probes on them.

BTW - thanks for the compliment. I actually found myself wondering what was going on here and got curious and decided that I wanted to know the answer myself. I like mysteries!

Let me know how it all works out in the end.
Jim Andrada is offline   Reply With Quote
Old March 3rd, 2008, 04:29 PM   #54
Major Player
 
Join Date: May 2006
Location: Toronto ON Canada
Posts: 731
Quote:
Originally Posted by Jim Andrada View Post
Well, the easiest way would probably be to use a reasonably sturdy extension cord with a double or triple outlet on the end and plug the lighting unit into it and stick the voltmeter probes into one of the unused outlets.
Ah, got it! I'll give it a whirl and let you know what are the results.
__________________
Mike Barber
"I'm laughing to stop myself from screaming."
Mike Barber is offline   Reply With Quote
Old March 4th, 2008, 01:09 AM   #55
Major Player
 
Join Date: May 2006
Location: Toronto ON Canada
Posts: 731
Woo-hoo!

Quote:
Originally Posted by Jim Andrada View Post
use a reasonably sturdy extension cord with a double or triple outlet on the end and plug the lighting unit into it and stick the voltmeter probes into one of the unused outlets.
IT WORKED!

Just as you said it would, adding a load to the circuit made the difference.

I also noticed a buzz coming from the dimmer! Should that worry me?

Also, something just occurred to me. I grounded the dimmer and the cord to the metal enclosure. Is this necessary, if the cord is already grounded at the outlet (source)?
__________________
Mike Barber
"I'm laughing to stop myself from screaming."
Mike Barber is offline   Reply With Quote
Old March 4th, 2008, 06:14 PM   #56
Inner Circle
 
Join Date: Feb 2007
Location: Tucson AZ
Posts: 2,207
I'm not sure about the buzzing - if it isn't too loud or overheating I'd probably not worry about it. I think one of the speed controls would still be a better idea than a hardware store dimmer, though.

Re grounding, without seeing the way you've wired it I can't say much. The principle is that the ground wire should run in an unbroken line all the way from the source to the destination. The ground wire is usually joined to the white wire at the service entrance where the wires enter the building or maybe some other point in a commercial building - it just provides an additional "just in case" return path and also protects agains inadvertent miswiring of the hot wire. Usually you can find a book on basic wiring at Home Depot or similar stores and one of these might be a worthwhile investment.

And I'm glad it seems to be working!

If Canadian electrical codes are like the US, they don't tell you what you have to do if there is a plug or other "disconnecting device" between your wiring and the mains. Neverhteless, it's still a very good idea to stay consistent with the code.
Jim Andrada is offline   Reply With Quote
Old March 5th, 2008, 01:49 PM   #57
Major Player
 
Join Date: Dec 2006
Location: Estes Park, CO USA
Posts: 426
Quote:
Originally Posted by Mike Barber View Post
IT WORKED!
Also, something just occurred to me. I grounded the dimmer and the cord to the metal enclosure. Is this necessary, if the cord is already grounded at the outlet (source)?
Yes, you did the right thing by grounding the metal box. Should a hot conductor come off in the box, it will trip your breaker (or blow your fuse) before creating a shock hazard to anyone touching the otherwise energized metal box.

Lot's of nice help here, folks. What a great forum.

Brian Brown
BrownCow Productions
Brian Brown is offline   Reply With Quote
Old March 5th, 2008, 07:16 PM   #58
Inner Circle
 
Join Date: Feb 2007
Location: Tucson AZ
Posts: 2,207
Yes, if the box is metal it should be grounded. Not necessary if it's plastic!

I think usually something that mounts into a box will ground it through the metal screws that attach it to the box, but is's best to check for sure using the continuity test funcion on your voltmeter.

Better safe than sorry!
Jim Andrada is offline   Reply With Quote
Old March 6th, 2008, 05:31 AM   #59
Regular Crew
 
Join Date: May 2004
Location: Honlululu, Hawaii
Posts: 30
Re: Voltage

Hi guys:

I too was a physics major and I did some electrical construction for a little while. Some of it was residential and some high voltage pole line work. I also did a lot of work as a theatrical electrician so I might be able to shed a little light here.

1. Thyrister or SCR (Silicon Controlled Rectifiers) work by turning on the voltage at controlled points in the waveform. The leading edge of the waveform looks like a square wave; it goes straight up or down (positive or negative) until it reaches the level that the sign wave is at when it turns on. The first experimental examples of these were very crude and use only one half of the wave form. Latter a full wave circuit was developed. The steep leading edge has a lot of harmonics in it so it can cause the filament to vibrate and sing or buzz. The best commercial products for professional use include at least an inductor to smooth out the leading edge and suppress the buzz.

2. If you have a florescent fixture with a "dimming" ballast, a circuit the was derived from the SCR dimmer circuit can dim those. The dimming ballast are expensive and hard to find. One manufacture modified the SCR dimmer circuit to turn a florescent into a strobe. The unit would drive 40 40watt tubes. I once used this for a black light effect. Yes I said 40 40watt tubes on one controller.

3. Contrary to "common knowledge", the voltage delivered by your local electrical utility is not always at the specified voltage. They work hard to do it but you must take into account the resistance of the lines from the transformer substation to the local transformer and then to your house or shop. I live about a block from a major substation and routinely see 135volts at my outlets. This is why in large industrial, commercial and specialized instillations you will find what are called "buck and boost" transformers. These are somewhat special autotransformers that have taps on them to select the amount of change and the direction of change desired.

4. A historical note: Well into the 1980's many the older theaters on Broadway in New York still had DC current supplied for most of the lighting so the only dimmers that could be used were resistance dimmers that came in 750W, 3000W and 6000W sizes and had to have a matching load on them. Because of this you could find old instruments with no lenses or even radiant heater coils as dummy loads. The dimmers were mounted in metal lined wood cases. The 3000W ones with 13 to a case and the 6000W ones with 12 to a case. These cases, when they had their shipping covers on, looked like a crate for an upright piano so they were called "piano boards".

The 750W dimmers came in rectangular boxes of 8, they were hooked up in groups of four so that each of these "auxiliary" boards had two leads that were each plugged into one 3000W dimmer. All the boards were manfully operated, the "piano boards had a mechanical linkage for a master handle that could move all the dimmers in that board together as long as they were all at the same level. The individual dimmers could have their handles disengaged from the master or could be set to engage the master when it reached the dimmers level. There was a switch for each dimmer and a maser switch for each light (3000W per dimmer) or heavy (6000w per dimmer) board.

Besides being heavy to move into place these boards put out a lot of heat. Each operator ran two boards, usually one light and one heavy. Most setups had 4 auxiliary boards fed from the light board; they were stacked 2 on each board. A big complex musical would have six or more boards, usualy 3 light and 3 heavy. With the dimmers throwing off heat and the dummy loads adding to the heat, the operators often striped to their underwear to survive. A complex move could involve an operator standing on one foot while sitting on both masters, moving one dimmer with his knee, moving one auxiliary dimmer each with each had and elbow and pulling one down with a string in his teeth. Lighting Designers were know to give an operator as many as four rehearsals to work out the choreography!


Grayson
Grayson L. Wideman is offline   Reply With Quote
Old March 7th, 2008, 12:36 PM   #60
Inner Circle
 
Join Date: Feb 2007
Location: Tucson AZ
Posts: 2,207
I remember the old theater light controls as well - not professionally, but when I was in High School I remember pulling the levers for some production or other.

I have a friend who's a lighting designer in NY and he tells me everything is digitally controlled these days. Heck, when I was in HS I don't think the "digit" had been invented yet. I actually remember clearly the first time I ever heard anyone around me say the word "computer" in general conversation - I think it was in the early 60's. I know I was getting on an electric bus at Harvard Square in Cambridge Mass when I heard some other passenger say it. I remember thinking that it must mean that the world was changing and maybe someday I could retire my slide rule.
Jim Andrada is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

Professional Video
(800) 833-4801
Portland, OR

B&H Photo Video
(866) 521-7381
New York, NY

Z.G.C.
(973) 335-4460
Mountain Lakes, NJ

Abel Cine Tech
(888) 700-4416
N.Y. NY & L.A. CA

Precision Camera
(800) 677-1023
Austin, TX

DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > The Tools of DV and HD Production > Photon Management

Thread Tools Search this Thread
Search this Thread:

Advanced Search

 



Google
 

All times are GMT -6. The time now is 11:51 PM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2017 The Digital Video Information Network