dimmers

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JDB3

Senior Member
Had a friend tell me, that the electrician that had wired their house, had told her not to use dimmers. That dimmers cause the electric bill to increase (or something to that nature). They cause electric bill to go up. Ever hear of an electrician saying that? :jawdrop:
 
I think that he's right if you're talking about the old fashioned dimmers that use a resistor to cause voltage drop. They waste energy by creating heat that is dissipated.

New electronic dimmers shouldn't be wasting energy because they don't work the same way.
 
I think that he's right if you're talking about the old fashioned dimmers that use a resistor to cause voltage drop. They waste energy by creating heat that is dissipated.


Are you saying that more electricity would be consumed than if the light was on for the same amount of time with a standard toggle switch?

No. I didn't really word that right. It doesn't use more energy, just uses the same amount while producing less light. So it wastes it in that way I guess.

Electronic dimmers can possibly "save" money but the older resistors just use the same as a toggle.
 

GoldDigger

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What is true is that, for incandescent bulbs only, if you want a particular light level you are better off putting in a small bulb than putting in a larger bulb and dimming it.
Issues of color temperature aside, an incandescent bulb becomes less efficient in producing light as the filament temperature decreases.
Lutron dimmers save energy only if you sometimes need the higher light level and sometimes don't, and are not able to modulate the light level by switching individual bulbs on or off.
 

gar

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If the load resistance is a tungsten filament light bulb, and you use a series resistor to adjust brightness, then as brightness is reduced the total input power will be diminished. But not as much as if the load was a constant resistance independent of applied voltage.

The tungsten filament lamp is a non-linear resistance with respect to applied voltage or current. Its curve is somewhat between a constant current and a constant resistance load.

If the load was a constant current type, then adjustment of the dimming resistor from maximum voltage to zero at the load would produce no change in input power.

.
 

Dennis Alwon

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Also if the dimmer is of the elv style from Lutron- electronic low voltage- then there is constant power to the unit and it will use energy even when the light is off. Gfci's and afci will do the same but I also believe it is a small demand
 

GoldDigger

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Also if the dimmer is of the elv style from Lutron- electronic low voltage- then there is constant power to the unit and it will use energy even when the light is off. Gfci's and afci will do the same but I also believe it is a small demand
Could you elaborate on that? Is the power (not just VA) significantly higher than for any other three wire dimmer?
 

Dennis Alwon

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Could you elaborate on that? Is the power (not just VA) significantly higher than for any other three wire dimmer?

W@hat do you mean by 3 wire dimmers- 3 way dimmer switch? The units I mentioned have a neutral which is used to energize electronics-- I assumed that there is some usage.
 

GoldDigger

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W@hat do you mean by 3 wire dimmers- 3 way dimmer switch? The units I mentioned have a neutral which is used to energize electronics-- I assumed that there is some usage.
Yes, I mean dimmers with a neutral, where the phase shift network will draw current except when the mechanical switch is open. Actually I guess the same would apply to two wire dimmers that rely on the loss as a return path.
Does the ELV not have a mechanical switch on the input side?
 

Dennis Alwon

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Yes, I mean dimmers with a neutral, where the phase shift network will draw current except when the mechanical switch is open. Actually I guess the same would apply to two wire dimmers that rely on the loss as a return path.
Does the ELV not have a mechanical switch on the input side?


The only ones I have seen are on the fan/light dimmer like the ones below. To be honest I have never seen anyone use them-- I think they put them there to stop kids from playing with them.

RC212-&-WC212_l.jpg
 

gar

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My guess is that most Lutron dimmers have a mechanical switch.

When that switch is open the dimmer will draw no current whether it is a 2 or 3 wire dimmer.

If the switch is not off, then both 2 and 3 wire dimmers, if there is a load connected will draw a significant amount of current in the minimum position.

If the switch is on, and there is no load, then a 2 wire dimmer will draw no current, but a 3 wire dimmer will require about 1 VA and 0.6 W.

.
 

penneyeugene

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Australia
We've considered buying dimmers for a few rooms in the house last month. This is the first time I heard that it can increase the electric load thoug. I think we'll have to think more about this for now.
 

gar

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penneyeugene:

As a general statement a dimmer used to control lights does not increase input power consumption as you dim.

A dimmer is used to either reduce average output voltage or current. If the load is linear, then reducing either voltage or current will reduce input power.

.
 

gar

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penneyeugene:

The type of light you want to dim is more important than whether to dim or not.

An incandescent light bulb, carbon or tungsten filament, is nicely dimmable from full to zero brightness with a Variac. Not so with standard commerical phase shift dimmers. For whatever engineering or marketing reasons commericial residential phase shift dimmers do not provide phase adjustment from 0 to 180 degrees, the range is more limited, especially with 2 wire dimmers.

Non-incandescent lights present problems relative to dimming whether by Variac (variable autotransformer), pulse width, or phase shift dimming. In my opinion there is no screw in CFL that has good dimming range compared to an incandescent on the low end. Some Cree LED bulbs dim fairly well with either a Variac or phase shift dimmer.

Not related to bulb type, but based on function I recommend a 3 wire dimmer, one that requires or can make use of neutral. The reason is because power to operate the dimmer is available whether or not the dimmer has a load. This means that when power input is applied to the dimmer that whatever was the dimmer setting at the time of power loss the setting will be restored on power up. Example: I have a 2 wire dimmer for my front hall lights. For normal operation the dimmer is set as low as it will operate. When the lights are turned off or there is a power interruption, then on power restoration the lights remain visibly off. The dimmer setting has to be raised to restore dimmer operation, and then again lowered. The dimmer is a 48 year old GE rotary knob type using a Triac. There is not much change in this type dimmer in present units.

Three wire dimmers are much more expensive than two wire dimmers, out of proportion with the cost of the added circuitry. You have to consider cost vs function when you decide what type of dimmer to use.

Do bench experiments with lights and dimmers that you might use to determine your direction. You can use a Kill-A-Watt EZ for power input measurements.

At my web page http://beta-a2.com/EE-photos.html photos P9 thru P18 are various graphs of some characteristics of incandescent and CFL bulbs. The low end of my incandescent curves did not go to zero because the wattmeter used had low voltage limitations. The power in my curves is the power to the bulb, and not power input to the dimmer.

.
 

mwm1752

Senior Member
Location
Aspen, Colo
energy codes have an exception in order to have a single switch by reducing the load draw by 50% which would include a dimmer. I do not think the exception would be in there is thier research did not conclude it would save energy.
 

gar

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EE
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mwm1752:

Can you explain what your post numbered 18 says?

energy codes have an exception in order to have a single switch by reducing the load draw by 50% which would include a dimmer.
How does a single switch correlate with a 50% draw? How do you produce a 50% draw?

Can you describe in precise detail the circuit to which you are referring.

.
 
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