Control/Dimming Flickering Lights
- Thread starterthelatinist
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RileyChilds
Member
What bulbs, our problem was that we had the wrong bulbs in the lights!
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Les
Well-Known Member
I don't see how that's possible unless they're arcing out (or if they're discharge sources). Interesting.
thelatinist
Member
Um ... BVT in the 75Q fresnels, GLA in the StarPars and Shakespeares, FFT in the SkyCycs. Nothing over 1000 W, and we have 2.4 kW dimmers.
By the way, today I shut off absolutely everything else in the building at the panels except for the outlets my console is plugged into and the fire alarm (which I do not have access to). I still duplicated the problem.
tyler.martin
Active Member
If you read the thread, the OP says he is using a Opto-Isolated Splitter, which while sounds like a common splitter, it is not. You are 100 percent correct, DMX does not like to be split -Passively. An opto-splitter uses transceivers to take the DMX signal and "clone" it many times, effectivly creating more of the same DMX signal. They also electrically isolate one signal from another, to keep any stray electrical signals away.
As for the issue at hand, I've had a similar issue with a CD80 rack, where the lights would flicker when they faded between 75 and 25 percent ranges, and it turned out to be a phase sense issue on the CIC, but since you have replaced that and the Phase reference card, I have nothing else to add...
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thelatinist
Member
So the guy from Northeast Utilities, the parent company of Connecticut Light & Power, came out and did our PQA. The long story short: he found nothing wrong with the power. He tested both at the CT panel and even after the 400-Amp sub-panel that feeds our theater. Using what he considered very close voltage tolerances the meter recorded only one event despite nearly constant flickering on our left leg, and the sine waves during that event looked perfectly normal. Total harmonic distortion was about 2% on the right leg and less than 4% on the left leg. If anyone is interested, I can post an image of the voltage and power curves during the one event recorded; they seemed perfectly normal.
He noted the same 3 Amps of current on the ground that we had previously seen, but disagreed that it was the result of induction in the conduit, since each conduit carries a conductor from each leg, which are 100% out-of-phase. The voltage was very low (~1V), which suggests that it must be coming from a resistive load. We are not sure how to proceed with that.
Since the PQA I have spoken to Joel from Century Lighting, who said that he was recently talking to a tech from Europe who has encountered similar problems on single-phase installations there and who said that there are settings in the C21 software that can be tweaked to fix it. He's getting more information for us; hopefully, this will not turn out to be another wild goose chase.
He noted the same 3 Amps of current on the ground that we had previously seen, but disagreed that it was the result of induction in the conduit, since each conduit carries a conductor from each leg, which are 100% out-of-phase. The voltage was very low (~1V), which suggests that it must be coming from a resistive load. We are not sure how to proceed with that.
Since the PQA I have spoken to Joel from Century Lighting, who said that he was recently talking to a tech from Europe who has encountered similar problems on single-phase installations there and who said that there are settings in the C21 software that can be tweaked to fix it. He's getting more information for us; hopefully, this will not turn out to be another wild goose chase.
If you are running loads at a dimmed level, with flicker, and getting only Vthd of 2-4%, you are doing great! In fact, that means there is a huge resistive load on your power feed and the dimming system is a small part of the load. On the other hand, if you are getting 2-4% Vthd with dimmers at full or at zero, then you have some disturbances on your grid but they should not be significant enough to cause problems.
The only way to really track that down is to be monitoring the current and then systematically turn breakers off one at a time until it drops or disappears. Then go see what is on that breaker or breakers and see if they are miswired [neutral/ground swap], or have Y caps built in to them. If it is a CE listed product, it might just do that. But for Y caps to cause this, there would be a lot of them on the power grid to cause 3A of current to ground.
Interesting. Single-phase power in Europe almost always refers to a single pole of power. If they have more poles of power, they will be called two-phase or three-phase. Only in the US does single-phase mean two poles of power, which is why I am on a crusade at work to use the terms split-phase and bi-phase so that we can better converse with people from around the world. Regardless, and back to the topic, I would expect dimming issues to only occur if there were a weak neutral feed, and with bi-phase, lights on both phases would flicker or change level. I think Joel is on to the right fix.
David
thelatinist
Member
Yeah, that was with about 100 A dimmed and about 150 A undimmed (the easiest way for us reliably to recreate the problem is to put everything else at full and use faders to adjust our 12 1000W Cyc. lights until it starts to flicker).
The only things on this sub-panel are 1) our dimmer rack and 2) a small sub-panel for other lighting and (I don't know why it was designed like this) our sound cabinet. Turning off the sub-panel did not affect the current over ground. We monitored the current as we slowly turned off the breakers on each dimmer, and found that the current slowly dropped to zero as we took out more and more dimmers. With all dimmers turned off there was almost no current to ground (around 0.1A).
It is possible that Joel only referred to single-phase when talking with me so as not to confuse me, since I am an American and in all of our discussions have referred to ours as single-phase rather than split-phase.
Yes, this is why it is so weird. The more total load we add, the greater the flickering problem becomes, but only on one phase. In the scenario I outlined above with 100 A dimmed and 150 amps undimmed, the 100 A of dimmed lights were all on the *non-flickering* phase. We have only ever seen flicker on that left leg.
i had a similar issue one time with our house lights flickering and it was on one row of lights, all just conventional ETC Pars using 750w lamps. The issue turned out to be a bad Power Block in the Dimmer itself. We used the ETC Smartpack and it was found in there. We checked the temperature and it was wildly hot compared to the others and that was because the Block itself was going out. May be something to check out in your setup...hope this helps.
JD
Well-Known Member
Sounds like there is a N/G bonding strap somewhere where it should not be. Defiantly something that requires a qualified person with proper protection, but with the rack locked out and tagged, the neutral would have to be lifted and then and metered with respect to ground. Since the only bond should be at the mains, the N/G should read an open circuit facing the dimmer rack. It will most likely read as a short. From there, it is a matter of following the neutral back and doing the same at each branch point.
EDIT: Just some more thoughts- Since the current flow in the ground is so much lower than what you would expect on the neutral, it indicates the ground path is of a much higher resistance. This would be a good indicator that the problem is pretty far out on a branch. No matter where this connection is, current will back-feed to that location, so even if the circuit is off, the loop will still be present. I don't think this is at a fixture level, but I have seen stranger things. If continuity shows at the rack neutral buss, it may be faster to remove the individual home-run neutrals from the circuits there then chase around the building.
In summary, this problem may have nothing to do with your primary issue, but it is a good place to start and should be corrected anyhow. In any diagnostic procedure, you always try to eliminate the things you know are wrong first.
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thelatinist
Member
Well, the only power cubes are in the C21 processor itself; and they were swapped out when Joel swapped out all of the electronics. The dimmers themselves are just a dual SSR module and a couple of chokes.
JD: Yeah, we're on that. There was originally a bonding strap in our 400A sub panel, which has since been removed. We will have to look around and see if there is a neutral-ground short somewhere.
thelatinist
Member
We turned off the power to the whole building at the main cutoff and disconnected the ground and neutral in the sub panel that feeds our theater. We tested for resistance across neutral and ground, expecting (or at least hoping!) to see infinite resistance. Instead we found only about 1 Ohm. So it appears that there is definitely some extraneous bonding somewhere. We're going to have to get an electrician in to track it down, I think.
Again, we don't know for sure that this is related to our flicker, but it's always a good idea to eliminate known problems when troubleshooting.
Anyone have any other suggestions?
JD
Well-Known Member
One Ohm.... Provided the meter was accurate, that may be pretty far out on a branch. (Higher resistance then I would suspect for a solid bond.) Might be worth the time to unplug all the fixtures. Since the dimmers and breakers only affect the "hot" carrier, a single fixture with an N/G short would provide back-feed for the whole system even if the breaker on the offending circuit was switched off. As labor intensive as it is, the full "unplug" test still sounds like the least expensive experiment on the list.
Yet another possible problem may be a simple N/G reversal on a fixture plug. The fixture would still work fine, but the neutral would be tied to the frame of the fixture and find it's path to the ground through any of the other fixtures mounted on the same pipe.
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tyler.martin
Active Member
Power Cube is a bit of a slang term for the SSR modules. Every dimmer module has a Power Cube/SSR in it.
thelatinist
Member
We took or SkyCycs down today to move the pipe they were on. On a whim we decided to open them up and check the connections. Everything inside was solid, but we tried checking continuity across ground and the other connectors in the plug and, sure enough, the first one we tried had continuity across ground and hot. Opened up the connector, and the ground and neutral pins were swapped!
So we opened up the connectors on all twelve of them and found five others with disconnected ground conductors in the plug. At least one of those was shorted across neutral and ground, and another was shorted across ground and hot! The wiring in all of them was really shoddy: the conductors were overstripped so much that I'm amazed more of them weren't shorted, and the strain relief on the stage pin connectors was installed improperly for the gauge and insulation.
Needless to say, I was not happy. The swapped neutral and ground must have been there since the theater was built six years ago, but with the shoddy wiring the other shorts could have developed at any time. We'll be taking down all our fixtures this week and checking the connections and connectors. I'm also going to open up all our outlet boxes and strips and check the grounding and insulation. And I'm going to get in an electrician to help us track down the rest of our grounding issue.
Most importantly, I'm greatly relieved that nobody was hurt by these shorts. Yet more Validation for my safety procedures.
David Ashton
Well-Known Member
I won't say "I told you so"
" logged this earlier, now disappeared, the most obvious, common problem causing flickering is a bad neutral connection in the dimmer and this could cause load related flickering, another vaguely possible fault is an earth neutral swap on a light, sending current down the earth and lifting it."
but I did
" logged this earlier, now disappeared, the most obvious, common problem causing flickering is a bad neutral connection in the dimmer and this could cause load related flickering, another vaguely possible fault is an earth neutral swap on a light, sending current down the earth and lifting it."
but I did
When you're right, you're right. You've earned the right to gloat.
Reading back through the posts, it looks like a few people got it (you in post #20 and DavidNorth in post #28 and JD in post #73). The OP was really close to solving it in post #12 when he removed some of the SkyCycs, but not all of them. Now I have a few questions:
Did the fact that this was on single phase power matter at all? Would the same thing happen with three phase power?
Why did everything work correctly when the OP put all the instruments on one leg for his show?
Did the transformer shut off because everything was on one leg, or was this simply a coincidence?
In the "Monday morning quarterback" department, what could have been done to solve the problem more quickly, or does it look like the proper steps were taken? Should the utility company or any of the electricians or support people have figured this out earlier, or was this a tough one to track down?
The OP had a bonding strap removed from a 400 amp sub panel. Should that be replaced?
I followed this thread from the beginning and found the process of troubleshooting extremely interesting and educational. It looks like fixing a flickering problem also corrected an unsafe wiring issue too. In the end, thelatinist may now have a few grey hairs, but the students will be safer.
David Ashton
Well-Known Member
Some parts I can answer, it absolutely can happen on 3 phase, it could not happen with rcd breakers fitted, as in Australia,
I am most surprised that it did not create havoc with the sound system, when I had a similar problem years ago whenever I brought up that channel the earth lift made the sound noisy, which was how I isolated it quickly.A big factor is how good the earth is, if it carries the current without lifting you can get away with it, but as soon as your earth is high impedance you're in trouble.
the idea that all this earth current was induced was obviously wrong
"e. Checked for and found amperage but no voltage on ground. Spent several hours chasing this amperage. Ultimately this amperage seemed to be induced current in the ground wire, which ran through the same conduit with 400-amp feed(s)"
response on Feb 4,
"If we can narrow it down to a single fixture/dimmer or set of fixtures/dimmers we will certainly check that. Thanks!"
gloat gloat.
I am most surprised that it did not create havoc with the sound system, when I had a similar problem years ago whenever I brought up that channel the earth lift made the sound noisy, which was how I isolated it quickly.A big factor is how good the earth is, if it carries the current without lifting you can get away with it, but as soon as your earth is high impedance you're in trouble.
the idea that all this earth current was induced was obviously wrong
"e. Checked for and found amperage but no voltage on ground. Spent several hours chasing this amperage. Ultimately this amperage seemed to be induced current in the ground wire, which ran through the same conduit with 400-amp feed(s)"
response on Feb 4,
"If we can narrow it down to a single fixture/dimmer or set of fixtures/dimmers we will certainly check that. Thanks!"
gloat gloat.
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thelatinist
Member
I know you're all excited by this development, but having been burned too many times by potential solutions that didn't solve the problem, I won't be declaring anything solved until we re-hang all our lights and thoroughly test everything. It's promising, I know, but a few facts keep me from being too optimistic:
1. We did not have this issue for the first five years we were using this instrument,
2. When we had everything on one leg (including this instrument) we had no flicker,
3. This instrument has always been on the right leg, which has not been the flickering leg, and
4. We still seem to have continuity across ground an neutral even with these instruments removed.
I'll let you know when we've tested everything and know more.
1. We did not have this issue for the first five years we were using this instrument,
2. When we had everything on one leg (including this instrument) we had no flicker,
3. This instrument has always been on the right leg, which has not been the flickering leg, and
4. We still seem to have continuity across ground an neutral even with these instruments removed.
I'll let you know when we've tested everything and know more.
thelatinist
Member
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