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Joined: Jan 2005
Posts: 5,445
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Cat Servant
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Geoff has nailed it ... not every photocell, motion sensor, timer, or other control works with every kind of light. CFL's have really brought this issue into focus.

The fast flicker is almost a guarantee that there are components fighting each other.

The only other thing to check is your grounding. Many controls and ballasts use the ground wire as a 'neutral,' and a poor ground path can cause problems like this.

Joined: Nov 2007
Posts: 764
K
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It almost sounds as if someone installed one of those 911 flasher switches in place of a standard on/off switch, but since you say their on a photocell, I assume this is common area lighting, so there probably isn't even an inside wall switch that the tenant or anyone else could access.
If that somehow turned out to be the case though, they usually have a bypass position so switch will operate on/off normally. I know at least the ones that Leviton makes have that feature anyway.

Joined: Oct 2000
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Broom Pusher and
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Quote

To better describe the flicker, it is a constant and consistent on/off/on/off with it pausing just a fraction of a second before it changes (like someone is moving the light switch up and down as fast as they can)


This sounds more like an Available Voltage / Circuit issue, as opposed to a False Triggering Photocell (P/C false triggered by reflected light from the Fixture's Lamp).

If the issue was from False Triggering, there should be at least 2-3 Seconds delay for the "OFF" Cycle, and at least 2-3 Seconds delay for the "ON" Cycle.

Apparently the P/C's Relay is closing upon Energizing the Fixture (as it would do normally); however, the Voltage drops rapidly and excessively under the Load of the Lamp, Ballast & Relay Coil (during inrush).

The Voltage Drop is high enough to cause the P/C's Relay Coil to "Drop Out" -
  • which then opens the Circuit to the Ballast -
  • which then reduces the Load on the Circuit at the Fixture -
  • which results in the Voltage rising to "Normal" again -
  • which causes the P/C to close the Relay -
  • which connects the Ballast / Lamp to the Circuit -
  • which places the Circuit under Load + Inrush -
  • which causes the Circuit's Voltage to drop excessively -
  • which causes the P/C's Relay Coil to "Drop Out" -
  • which opens the Circuit to the Ballast -
  • (repeat rapidly and endlessly)


Then again, the area of the affected Fixture might be possessed by a Practical Joking Poltergeist, which will require the services of an Electrical Exorcist... grin

--Scott (EE)


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Jul 2007
Posts: 1,335
S
Member
Have you tried to swap out with a fixture at a different spot? I.e., take the flickering light and swap it with a similar light at a different location known to work good. If the first flickering light still flickers at a "known" good spot, it's the light. If a known good light flickers in the location. It's most likely an environment issue. Light from some where subtle enough to piss you off without you noticing it.

Here's a long shot though. Can you take a voltage reading with a solenoid based volt meter? Perhaps there's a weak connection. Only time I use a DMM to measure voltage is whin I know I nave a good solid connection to the source.


"Live Awesome!" - Kevin Carosa
Joined: Jul 2004
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G
Member
Times like this is when you just want an edison base with a 100 watt bulb in it. We would not be talking about low voltage and bad connections. Take out the PC and watch the bulb.

I do agree, swap it with a known good one. Maybe hook up a keyless with an A19 in it and then look at the voltage, flicker or whatever.
If the power is good and a known good unit still fails, that type will not work there. Try something else. Maybe use a remote photo cell.


Greg Fretwell
Joined: Jun 2004
Posts: 1,273
T
Member
The TOP suspect is a marginal neutral return.

This return leg/ or grounding conductor will read 'fine' on a DMM, even a small analog meter.

Once loaded the voltage differential will collapse...

Then see Scott35, above.

The poor neutral can exist MERELY by being too far from the panel -- resulting in excessive impedance.

While the neutral is the TOP suspect, even the 'hot' (120V) may have too much impedance or too much of a parallel load. ( much more uncommon: 'make-up' on neutrals is very commonly much more sloppy than the 'hot' conductor.)

In your case, I would not be surprised if the load was wired off a 'house' panel. (on the landlord's dime) This will usually be a dinky panel back near the Service entrance -- with just perhaps ONE circuit dedicated to this lighting run. (count up the fixtures on this circuit -- too many and you're into 'multi-vibrator land.')

&&&&

I've seen this 'multi-vibrator' effect on every manner of electronic 'ballast' or power conversion logic -- especially in site lighting where the distances are LONG.

Upsizing the conductors -- especially the neutral solves the problem, nothing else.

The very size of your building is suspect: this particular fixture 'smells' like it's very far from your distribution panel.

It's as common as dust for the installation crew to NOT spot the voltage drop because of impedance on such long neutral runs -- which will, obviously, never be line of sight.

I've seen this defeat countless foremen and j-men.

Multi-vibrators are worth studying on Wiki just for an understanding of engineered flip-flops.

By the way, your computer utterly depends upon multi-vibrator logic, they always have.

As intelligent devices pervade our lives, you'll encounter this frustrating tick more than once.

And, with this, you're the 'smartest wire-man' in your complex!

Last edited by Tesla; 01/25/15 02:42 AM.

Tesla
Joined: Nov 2005
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J
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Is it just me? I could've sworn that our O/P stated that the lamp stayed on solid when he placed opaque electrical tape over the photocell. Don't you think that all the various line anomalies,(Love that word!), would still be there with tape on the sensor? So I still want to know how long it takes for a normal fixture in a normal location to switch on with the photocell blocked, and turn back off when unblocked, in broad daylight. I don't think that any photocell ckt used in a lighting application, should react as quickly as he described, so knowing the normal response time is important. He could be getting RFI in a higher impedance part of the circuit, causing it to act like a relaxation oscillator. But I would only suspect something like that if the normal response is slower than what he's seeing. If a normal fixture can really switch on and off that quickly, I would use the pop can trick, to block light coming from different angles.
Joe

Joined: Jan 2005
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Cat Servant
Member
Joe, when I test photocells, it typically takes about three minutes for the lights to come on, after I have covered the sensor with black tape.

When I first apply power to the photocell, it takes about half a minute for the photocell to activate the lights - and another minute or two to shut off the lights if it's sunny out.

If a photocell is being fooled by reflected light, the light can cycle fairly quickly; any HID light will take a bit to come up to full brightness and trip the sensor. By "quickly" I mean maybe 15 seconds on followed by three minutes off. Reflected light will not cause the extremely fast cycling described by the OP.

Joined: Jul 2004
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G
Member
I keep coming back to my original guess. The PC is not compatible with a CFL and I bet it works fine if he put an A19 in the circuit.


Greg Fretwell
Joined: Nov 2005
Posts: 827
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J
Member
Reno, I agree with you on your typical lighting photocell observations. I would expect that to be how our OP's behave but I want to see his answer. They are designed with very long time constants.
Greg, he tells us that they are designed for CFLs and that they work fine elsewhere.
Todd, you said that you observed the voltage. Does that mean that you used a Fluke or similar meter with Min/Max Record? Have you contacted the mfg to see if they have reports of fixtures behaving this way? Are there any obvious RF sources in that location?
Joe

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