Lights flickering when Dimmed

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Sharpie

Senior Member
Location
PA
OK guys,

A customer called me saying "Within the last couple of weeks, our lights flicker whenever they are dimmed. The only way to get them to light steady is to put the dimmer at full brightness".

I installed at least one of these dimmer a couple of years ago, but the others were already there.
I have not gone to their house yet to check voltage and such. I just wanted to know if any of you have run into simillar problems and what causes you could think of.

Also, they have not had any electrical work done recently, and have not changed any lamps (they are incandescents).

If this post is in the wrong location, would one of the moderators please move it to the appropriate one?

Thanks
 

Sharpie

Senior Member
Location
PA
It started with one dimmer, then another started to do it. Not all of the house's dimmers are doing it though.

Now that I think of it, the two dimmers that are doing it might be on the same circuit. I don't know that for sure though.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
You can check the voltage for sure but it may be as simple as new dimmers. Make sure the dimmers match the load and the type of light , i.e. fluorescent, low voltage magnetic vs electronic, etc. Let us know what you find.
 

dbuckley

Senior Member
Have they used lower wattage bulbs? They may have unintentionally got below the dimmer's minimum load capability and under those circumstances you get flickering.

Though CFLs would be a good trick too :)
 

Rick Christopherson

Senior Member
That's strange, because I just had the same thing happen in my home office yesterday. Single fixture with two incandescent bulbs. It made no difference where on the scale the dimmer was set (except for full-on) the lights would flicker at a steady rate of a couple times per second.

I thought that maybe it was a dirty wiper, but even exercising the lever made no difference. Next day, everything was fine.
 

Sharpie

Senior Member
Location
PA
My customer, who I believe is telling the truth (though I don't believe all customers), told me that they haven't had to change any of the lamps (there the same lamps that were there two years ago). The lamps that they have in place are incandescent (which I previously stated). Rick, that's odd that you're seeing that too. I don't know if undervoltage or maybe a surge could have caused it. The load didn't change.

Anyway I won't be able to get there right away (maybe in the next week or so).

Thanks for the replies so far. We'll get this figured out.
 

gar

Senior Member
091120-1004 EST

Sharpie:

I ran a quick test on an inexpensive Leviton rotary dimmer with a 15 W lamp load. This dimmer, unknown part number, but maybe like a 6681, worked very well over a wide range of voltages, 60 to to 140 V. There were some spots where there was a slight tendency to have a 1 second period flicker. This was about 85 V. I could not maintain the flicker nor repeat it.

This dimmer is a two wire dimmer and exhibits a common characteristic that if set at a low dimming level and power is removed and reapplied that the light does not turn on. After power is applied it is necessary to raise the setting to get the dimmer started again.

Sometime back I bought an expensive three wire Lutron dimmer. This one was designed for fluorescent dimming. In my experiments with it on an incandescent lamp this problem characteristic was eliminated, at least over the range of dimming possible. This improvement with a three wire dimmer I would expect. However, the particular dimmer was too limited in its lowest setting.

Actually this dimmer has four wires, the fourth is full voltage all the time when on for filament excitation of fluorescent lamps. The dimmer function alone is a three wire design.

Check and see if there are supply voltage variations that might be the origin of the flickering. Under dimmed conditions a small voltage change may be amplified in its effect.

Dimmers of different manufacturers or models might have the possibility of oscillating and causing the flickering.

.
 

gar

Senior Member
091121-1610 EST

An observation of dimmer flickering, but it does not match the symptoms of the original post.

Walked into a room where my wife had set a 300 W Torchiere to a dimming midpoint and the light was flickering. It was a narrow setting range where the flickering occurred. This is clearly a defective dimmer. In this case it is rather self-evident that the dimmer is faulty. Has this characteristic always existed? I do not know.

.
 

hurk27

Senior Member
two reasons I have found for this condition was one over loaded leviton dimmer, which the owner reduced the wattage of the lamps and it stopped, two was where a home owner tried to use two 3-way dimmers in place of 3-way switch's and it put one dimmer in series with the other causing the lights to strobe.
 

ccrtech

Member
If these are Lutron manual dimmers, like ariadni or toggler, they will not work with the Sylvannia Capslyte Halogen lamps (par 30), or they will work for a period of time. I had a job where the dimmers would last for about a month before this would start happening. Lutron says it's the lamps, a Nova T dimmer was the fix in this case.
 

gar

Senior Member
091130-0657 EST

Can someone define what is different about a Nova dimmer in comparison with other dimmers? I am really asking what is the internal circuit difference.

There should be relatively little difference in inrush current between a standard incandescent and a halogen.
Standard 100 W cold resistance 9.4 ohms, hot 144 ohms, ratio 15.32 to 1.
Halogen 90 W cold resistance 10.4 ohms, hot 160 ohms, ratio 15.38 to 1.
So why should a halogen be a problem?

The inadequate meager information provided by Lutron may imply somewhat better heatsinking for the Nova. It also may be a three wire device where the EGC is used to provide a current supply to the internal electronics. But no way to know without disassembly of a unit.

.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
I have heard that flicker caused by voltage fluctuations is far more evident on dimmed incandescent lights.

Perhaps a new load added to the same supply transformer (possibly at a different house) is causing the flicker.

-Jon
 

Sharpie

Senior Member
Location
PA
I have heard that flicker caused by voltage fluctuations is far more evident on dimmed incandescent lights.

Perhaps a new load added to the same supply transformer (possibly at a different house) is causing the flicker.

-Jon

That's an interesting thought Jon. I'll interview the neighbors (and try to pick up some new customers at the same time:grin:)

I'm supposed to go and check out the dimmers today. I have replacements ready in the truck. I'll let you guys know if I find anything.

Did I mention that these have decorative metal cover plates? They are a heavy metal (1/8" thick steel?). I wonder if over a couple years the heat is killing the dimmers?
 

gar

Senior Member
091201-0815 EST

Sharpie:

The more heatsinking you provide the lower the temperature rise of the components on the heatsink. I suspect the heavy front plate is to provide a larger heatsink surface area, and conductivity to that area.

Yes, excessive internal temperature may produce a gradual degradation, or a delayed abrupt failure.


winnie:

On an inexpensive phase shift dimmer it is likely that input voltage variations produce a shift in the phase shift trigger point of the dimmer affecting the brightness as well as just the voltage variation.

.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Maybe a neighbor on the same transformer has an electric tankless water heater.

Is the flickering a steady flicker, or more of an intermittent change in brightness?
 

Sharpie

Senior Member
Location
PA
Ok, I got to the customer home, started to check out the dimmers in question. The one that I had installed nearly three years ago would not flicker for me. The other one (that I did not supply/install) would flicker at any point on the dimmer except for full bright. It was a steady flicker.

I checked voltage, everything good (124 or so).

The load is incandescent and well within the min-max range of the dimmer.

I replaced the faulty dimmer and everything was good.

I suspect that the unknowing homeowner got a cheap version of the Ariadni from big orange or blue.

I should also note that the faulty dimmer was not grounded (could that cause early failure?)

Well, at this point I'll just have the customer watch and see. If they start having any other problems it'll be time for more investigation.

But I suspect were ok now.

Thanks everyone.
 
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