Film-Tech Forum ARCHIVE: Flickering Auditorium Lights

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Posted by Aaron Mehocic (Member # 15) on 11-18-2006, 11:48 AM:

Our auditorium lighting is flickering intermittently throughout the day. We are using Smart 3K Dimmer units with new SCR cards attached to Neumade Maxi 12XPC automations. Originally it was thought that by keeping the automation off and the emergency by-pass switch on, the problem would go away. That has since been proved false.

One thing I have noticed, however, is that one of the dimmers has a fan blowing air into the unit, whereas the other units do not. Even though all three flicker, the blower dimmer does it FAR LESS. Will retro-fitting the dimmers with a blower fan solve the problem?

Posted by Louis Bornwasser (Member # 3063) on 11-18-2006, 12:06 PM:

USUALLY some flicker at low levels is normal; particularly with dimmers without a quality choke.

"Strobing" is usually caused by wiring with common neutral or uninsulated neutral. Also sometimes caused by "unparallel routing" of wires. IOW: both hot and neutral wires need to be insulated and the same length. Good luck. Louis

Posted by Jack Ondracek (Member # 1466) on 11-18-2006, 12:11 PM:

Your saying that the flicker is still present when the bypass switch is on is interesting.

I would confirm that the bypass switch actually does just that. If it routes the incoming power directly to the output terminals, your flicker can not be caused by the dimmer.

It would seem strange if a bypass did not work that way. Leaving the SCR in the circuit would be asking for problems if it was to fail.

Posted by Louis Bornwasser (Member # 3063) on 11-18-2006, 02:41 PM:

Adding this after rereading post: Eliminate the automation. The Smart "emergency bypass" switch does not actually bypass the scr, but just tells it to go full up.

You could add a full voltage, full current bypass switch by connecting input to output strictly for diagnostic purposes. Louis

Posted by Gordon McLeod (Member # 33) on 11-18-2006, 03:26 PM:

Smart used a very large toroidal filter choke so that shouldn't be the problem
I would check for spikes on the AC mains and neutral noise
also if the SSR block has two gate leads try reversing them
Also on the circuit board replace the optocoupler

Posted by Brian DeCiancio (Member # 1422) on 11-18-2006, 05:40 PM:

This may or may not help but, the dimmer manual for the units used at the theatre I work at say that flickering, strobing, etc. can and usually is caused by lighting loads that share a neutral.

Posted by Oscar Neundorfer (Member # 458) on 11-20-2006, 04:13 AM:

Has this problem existed from the initial installation or has it recently started? You said it was "flickering intermittently throughout the day". Have you been able to correlate the flickering with any other event at the theatre such as large motor loads kicking on, like HVAC, for example?

The three dimmers ideally should all be on the same phase, and absolutely should not be sharing neutrals. Each should have a separate neutral running all the way back to the panel. Same goes for the lighting loads. In some cases where the 3 phase and neutral were brought to the console and distributed in the console, neutrals all the way back to the panel are not always easily done.

In any event make sure the neutrals are not daisy chained from one to the next, to the next, and then back to the neutral buss bar, whether the buss bar is in the console or back at the distribution panel.

I can't explain why the one with the fan flickers less. The only reason for the fan was that this model had a slightly higher inductance choke for less lamp singing efect, and would run slightly hotter. So the fan kept it cooler. Perhaps the higher choke inductance is making it slightly less susceptible to flickering effects which might be caused by wiring issues or other causes.

One other suggestion is to go through the system and make certain there are no loose connections on any of the wiring terminals either on the dimmers or at the distribution terminals. Over time, things tend to loosen up and can cause problems. Check hots, neutrals, and grounds. Also make sure each dimmer is securely grounded with a separate ground wire from the ground terminal back to the distribution ground buss. As usual, take the proper precautions and remove power at the breakers before doing this type of work.

SMART dimmers were known to be fairly problem free except for some issues with early models driving magnetic low voltage loads such as Tivoli lighting. This was usually manifest as breaker tripping at turn on, not flickering.

Hope something here helps.

Oscar