lights flickering or dimming
- Thread starter wainscott
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
It may depend on the amount of dimming. In some cases this dimming may be normal and I believe it is a function of the transformer. I have seen some dimming when the transformer was too far from the home thus creating a vd when large loads would start.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
141206-2033 EST
A small change, drop, in voltage for a short time will produce a noticeable dimming, flicker, in the light intensity of an incandescent light. I can detect a 1 V change.
Every practical electrical voltage source can be approximated as as an ideal voltage source, perfectly constant voltage, and a series impedance, called the internal impedance.
Suppose the voltage source is 100 V, and the internal impedance is 0.1 ohms. A change in current of 50 A will produce a change in voltage drop of 5 V. The initial current to an air conditioner compressor could easily be 50 A. Number 6 copper wire is about 0.4 ohms per 1000 ft. Besides copper wiring there is considerable internal impedance in the distribution transformer.
Use GE dimmable CFLs without a dimmer, and you may not see as much flicker as you do with incandescent bulbs.
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A small change, drop, in voltage for a short time will produce a noticeable dimming, flicker, in the light intensity of an incandescent light. I can detect a 1 V change.
Every practical electrical voltage source can be approximated as as an ideal voltage source, perfectly constant voltage, and a series impedance, called the internal impedance.
Suppose the voltage source is 100 V, and the internal impedance is 0.1 ohms. A change in current of 50 A will produce a change in voltage drop of 5 V. The initial current to an air conditioner compressor could easily be 50 A. Number 6 copper wire is about 0.4 ohms per 1000 ft. Besides copper wiring there is considerable internal impedance in the distribution transformer.
Use GE dimmable CFLs without a dimmer, and you may not see as much flicker as you do with incandescent bulbs.
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ptonsparky
Tom
- Occupation
- EC - retired
Newer home, all electric, cfl and led lighting, we notice no dimming. I agree with Gar, except mine are Sylvania.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
141206-2244 EST
I have a number of plots of light intensity vs voltage on my website for various bulbs. See photos P9 thru P18 at http://beta-a2.com/EE-photos.html .
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I have a number of plots of light intensity vs voltage on my website for various bulbs. See photos P9 thru P18 at http://beta-a2.com/EE-photos.html .
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gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
141207-1958 EST
ritelec:
Much of what is on my site to which I route people on this forum is to provide background information, mostly experimental, on various basic electrical concepts.
Where you do not understand something please ask questions. Some of the measurements or concepts that I present, you may or may not be able to duplicate with equipment in your possession. One you may be able to do is a 4-terminal resistance measurement, to measure the resistance of a 10 ft thinwall and a 10 ft rigid conduit. Then compare the two. It might be better to measure a longer piece of rigid and actually compare resistance per foot.
Comparison of light bulbs and their intensity variation with voltage can be done without a Variac by use of several different resistors in series with the bulb. A 60 W incandescent rated at 120 V is 0.5 A, and a resistance of 120/0.5 = 240 ohms. A 1500 W heater is 12.5 A at 120 V or 9.6 ohms. And a little less at room temperature with no current flow.
Measure an actual heater with an ohmmeter. Here I will ballpark its value at 10 ohms. Put this in series with the 60 W bulb and the voltage drop will be about 10*0.5 = 5 V. Short and unshort the heater and the bulb voltage will change about 5 V.
For a smaller change a lower resistance is needed. For a 1 V change 2 ohms is needed. A cold (room temperature) incandescent filament is about 11 ohms. About six 100 W incandescent bulbs in parallel may be close to 2 ohms.
At six 100 W bulbs the current per bulb would be about 0.08 A. This may produce enough filament heating to require some more parallel bulbs to actually get a 1 V drop. A 1.5 V battery could be used to test the approximate resistance at 1 V. I tried this and got 0.087 mA with 1.57 V after a short stablization time. R = 1.57/0.087 = 18 ohms.
Using a different source with my 100 W test bulb 1 V results in about 0.065 A, or about 17 ohms. Thus, about 0.5/0.065 = 7.69 bulbs, and 7 or 8 bulbs will get close to a 1 V drop. Fewer bulbs will produce more voltage drop for other test points.
You do not need precise voltage drops in this type of experiment to illustrate how sensitive the eye is to small voltage variations to an incandescent.
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ritelec:
Much of what is on my site to which I route people on this forum is to provide background information, mostly experimental, on various basic electrical concepts.
Where you do not understand something please ask questions. Some of the measurements or concepts that I present, you may or may not be able to duplicate with equipment in your possession. One you may be able to do is a 4-terminal resistance measurement, to measure the resistance of a 10 ft thinwall and a 10 ft rigid conduit. Then compare the two. It might be better to measure a longer piece of rigid and actually compare resistance per foot.
Comparison of light bulbs and their intensity variation with voltage can be done without a Variac by use of several different resistors in series with the bulb. A 60 W incandescent rated at 120 V is 0.5 A, and a resistance of 120/0.5 = 240 ohms. A 1500 W heater is 12.5 A at 120 V or 9.6 ohms. And a little less at room temperature with no current flow.
Measure an actual heater with an ohmmeter. Here I will ballpark its value at 10 ohms. Put this in series with the 60 W bulb and the voltage drop will be about 10*0.5 = 5 V. Short and unshort the heater and the bulb voltage will change about 5 V.
For a smaller change a lower resistance is needed. For a 1 V change 2 ohms is needed. A cold (room temperature) incandescent filament is about 11 ohms. About six 100 W incandescent bulbs in parallel may be close to 2 ohms.
At six 100 W bulbs the current per bulb would be about 0.08 A. This may produce enough filament heating to require some more parallel bulbs to actually get a 1 V drop. A 1.5 V battery could be used to test the approximate resistance at 1 V. I tried this and got 0.087 mA with 1.57 V after a short stablization time. R = 1.57/0.087 = 18 ohms.
Using a different source with my 100 W test bulb 1 V results in about 0.065 A, or about 17 ohms. Thus, about 0.5/0.065 = 7.69 bulbs, and 7 or 8 bulbs will get close to a 1 V drop. Fewer bulbs will produce more voltage drop for other test points.
You do not need precise voltage drops in this type of experiment to illustrate how sensitive the eye is to small voltage variations to an incandescent.
.
Thanks , I figured it may be voltage drop but couldn't understand why when the service was sized correctly and all branch circuits as well. So I'm assuming the utility transformer and the impedance . Thanks that makes more since.
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gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
141207-2232 EST
The human eye and brain combination can detect light intensity changes much smaller than that of a 1 V change.
In 1953 I was a subject in an experiment on signal detectability that envolved light level experiments. This was conducted by my psychology professor for the U of M Electronics Defense Group under a military contract.
The experiment was known as a signal known exactly type. This meant we knew the time of occurrence, four possible locations for a single spot, and that a spot would occur. The spot locations were randomly selected. From a chance probability you would be able guess correctly 25% of the time. Over a large sample of trials under the same set of parameters (background intensity, spot intensity relative to background, and duration) any correct answers in excess of the 25% random probability implied a degree of detection capability.
After you had been trained by being a subject for a period of time it was possible to show that you could detect signals weaker than what you thought you could detect. The spot intensities were so low that you did not consciously realized that you detected a signal.
In my home most of my motor loads do not cause a noticable light flicker, but my neighbor's air conditioner is detectable.
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The human eye and brain combination can detect light intensity changes much smaller than that of a 1 V change.
In 1953 I was a subject in an experiment on signal detectability that envolved light level experiments. This was conducted by my psychology professor for the U of M Electronics Defense Group under a military contract.
The experiment was known as a signal known exactly type. This meant we knew the time of occurrence, four possible locations for a single spot, and that a spot would occur. The spot locations were randomly selected. From a chance probability you would be able guess correctly 25% of the time. Over a large sample of trials under the same set of parameters (background intensity, spot intensity relative to background, and duration) any correct answers in excess of the 25% random probability implied a degree of detection capability.
After you had been trained by being a subject for a period of time it was possible to show that you could detect signals weaker than what you thought you could detect. The spot intensities were so low that you did not consciously realized that you detected a signal.
In my home most of my motor loads do not cause a noticable light flicker, but my neighbor's air conditioner is detectable.
.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
When that AC compressor starts it may have an instant current of over 100 amps for just a few milliseconds and then rapidly starts to drop and maybe reaches a stable current in the range of 15 to 35 amps (depending on size of unit) within a couple seconds. The larger kVA capability of the supply transformer the easier it is for it to deliver this current without a significant drop in output voltage. Size and length of conductors between the source and load will also "choke" the voltage during this short burst of current. The sag in voltage can then be followed by an overvoltage in some cases where there is poor regulation or even with a portable generator application the generator governor sees the sudden voltage drop and tries to increase engine speed and then the following sudden voltage rise goes too far because generator is now running too fast.The smaller the generator in comparison to the load the worse this effect can be.
- Occupation
- Licensed Electrician
You mean it is not from low brow installers using 14AWG....Dang!
JDB3
Senior Member
- Location
- San Antonio, Texas
Years ago, wired track houses. Owner complained of lights dimming when "new" refrigerator came on. Went to check it out. Yep, they dimmed. All connections good. Put amp meter on wires feeding refrigerator, 50+ amps on start up. Refrigerator turned from "new" to "just 3 years old".
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Considering an AC induction motor can draw up to 6 to 8 times full load current momentarily at start up this doesn't seem very unreasonable to me, whether new or 25 years old. Throw in long service conductor run, long feeder, long branch circuit - or any combination of those to add some voltage drop and you may lessen the starting current some, but probably increase the duration of what drop is experienced.
SAAPI
Member
- Location
- Boston, Massachusetts
HVAC systems typically are large inductive loads - when they turn on they cause a drop in the overall mains voltage.
Someone in our building put in one HVAC system for a 40,000 square foot building - with a huge motor - when the motor kicked in every incandescent light dimmed - and all the UPS systems went off.
Someone in our building put in one HVAC system for a 40,000 square foot building - with a huge motor - when the motor kicked in every incandescent light dimmed - and all the UPS systems went off.
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