horrorsix
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- Harrisburg PA
What is the difference between an electronic low voltage dimmer and a regular dimmer. I don't understand why you need an electronic dimmer to dim a transformer.
Low Voltage Dimmer????
- Thread starter horrorsix
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A regular dimmer, by virtue of how it chops the AC sine wave to do the dimming action, imposes a DC current on it's output which can cause transformer-based devices into core saturation or severe overheating. (As in letting out the magic smoke.)
An electronic type dimmer uses a different method of "modulating" the basic AC waveform so that it will have little or no DC current on its output.
If I could find them, I would post a picture of the two different waveforms and you can actually see the difference. But a regular dimmer basically flattens the tops and bottoms of a sine wave, and if you draw that out on a plot of amplitude and voltage, you'll see that the flat tops portion maintains a steady-state value (read: DC) over a much longer time that a "straight" sine wave.
An electronic type dimmer uses a different method of "modulating" the basic AC waveform so that it will have little or no DC current on its output.
If I could find them, I would post a picture of the two different waveforms and you can actually see the difference. But a regular dimmer basically flattens the tops and bottoms of a sine wave, and if you draw that out on a plot of amplitude and voltage, you'll see that the flat tops portion maintains a steady-state value (read: DC) over a much longer time that a "straight" sine wave.
A couple of dimmer output voltage waveforms.
Leading edge:
Trailing edge:
Unless the dimmers are faulty, there should no significant dc component in the voltage.
horrorsix
Member
- Location
- Harrisburg PA
A couple of dimmer output voltage waveforms.
Leading edge:
Trailing edge:
Unless the dimmers are faulty, there should no significant dc component in the voltage.
Thank you for you reply. That's what I was looking for.
gar
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090424-0802 EST
I would classify a Variac or some variable impedance device as a non-electronic dimmer. Anything else is probably an electronic dimmer.
A Variac or variable resistor (impedance) will not contribute a DC component to the output if there is no DC component in the input.
Now consider a phase shift type of dimmer, whether leading or trailing edge. If the turn-on or turn-off angle is not the same for the positive half cycle vs the negative half, then you will produce a DC component.
A DC component in an AC waveform applied to a transformer on either the primary or secondary side will add a DC bias to the hysteresis curve and produce a greater peak magnetizing current on one half of the AC cycle than the other half cycle. The effect is greatly dependent upon the shape of the hysteresis curve, and magnetic excitation level. The magnitude of excessive heating from the peaked current is a function of many factors.
In addition to magnetic saturation is the heating from higher frequency components in the non-sinusoidal waveform.
Note: a half wave rectifier and capacitor input filter on the output of a transformer produces a large DC component and peaked charging current. With appropriate design this can be made a reliable product. So DC in a transformer primary or secondary does not mean it won't work. It is design dependent.
The volt-time integral of the voltage applied to a coil with a ferro-magnetic core will determine how far into saturation the core is driven. To avoid an unbalanced hysteresis curve steady state operating condition the magnitude of the positive and negative volt-time integrals must be equal.
I have looked at the DC component of an inexpensive phase shift dimmer and it was not very large in comparison to full rated current of the dimmer.
Can you provide information on what a so called "electronic dimmer" is in comparison to a standard inexpensive phase shift dimmer (probably meaning leading edge because these are cheap to make with a Triac).? Even a Triac dimmer with added circuitry could dynamically adjust over a cycle or so to achieve an average DC output of zero.
I see no inherent reason a trailing edge dimmer is less likely to produce a DC component than a leading edge dimmer. However, it may be easier to design a circuit for zero DC output on a trailing edge dimmer. Here one could simply control the turn off point of the positive half cycle from the input control knob, and on the negative half control turn off to occur when the integral of the positive and negative half cycle currents become zero.
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I would classify a Variac or some variable impedance device as a non-electronic dimmer. Anything else is probably an electronic dimmer.
A Variac or variable resistor (impedance) will not contribute a DC component to the output if there is no DC component in the input.
Now consider a phase shift type of dimmer, whether leading or trailing edge. If the turn-on or turn-off angle is not the same for the positive half cycle vs the negative half, then you will produce a DC component.
A DC component in an AC waveform applied to a transformer on either the primary or secondary side will add a DC bias to the hysteresis curve and produce a greater peak magnetizing current on one half of the AC cycle than the other half cycle. The effect is greatly dependent upon the shape of the hysteresis curve, and magnetic excitation level. The magnitude of excessive heating from the peaked current is a function of many factors.
In addition to magnetic saturation is the heating from higher frequency components in the non-sinusoidal waveform.
Note: a half wave rectifier and capacitor input filter on the output of a transformer produces a large DC component and peaked charging current. With appropriate design this can be made a reliable product. So DC in a transformer primary or secondary does not mean it won't work. It is design dependent.
The volt-time integral of the voltage applied to a coil with a ferro-magnetic core will determine how far into saturation the core is driven. To avoid an unbalanced hysteresis curve steady state operating condition the magnitude of the positive and negative volt-time integrals must be equal.
I have looked at the DC component of an inexpensive phase shift dimmer and it was not very large in comparison to full rated current of the dimmer.
Can you provide information on what a so called "electronic dimmer" is in comparison to a standard inexpensive phase shift dimmer (probably meaning leading edge because these are cheap to make with a Triac).? Even a Triac dimmer with added circuitry could dynamically adjust over a cycle or so to achieve an average DC output of zero.
I see no inherent reason a trailing edge dimmer is less likely to produce a DC component than a leading edge dimmer. However, it may be easier to design a circuit for zero DC output on a trailing edge dimmer. Here one could simply control the turn off point of the positive half cycle from the input control knob, and on the negative half control turn off to occur when the integral of the positive and negative half cycle currents become zero.
.
- Location
- Massachusetts
Using Besoeker's great graphics :smile:
As I understand it the above waveform would come from a standard inexpensive dimmer and if used with a transformer the fast rise on the leading edge creates an inrush current each time possibly overheating the transformer.
The above trailing edge waveform would be what you would want to use with a transformer as the rise time in 'normal'.
As I understand it the above waveform would come from a standard inexpensive dimmer and if used with a transformer the fast rise on the leading edge creates an inrush current each time possibly overheating the transformer.
Trailing edge:
The above trailing edge waveform would be what you would want to use with a transformer as the rise time in 'normal'.
gar
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- Ann Arbor, Michigan
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- EE
090424-0935 EST
iwire:
A step change in voltage to an inductor does not cause a step change in current. Instantaneously you can not change the current in an inductor.
If I connect a battery thru a switch to a series L R circuit (inductance resistance), and the initial current thru the inductor at the time of switch closure is zero, then the current will be of the form (1-e^-tR/L). An exponential curve starting at 0 (1-e^0 = 1-1 = 0) and gradually rising to 1. The lower the resistance the longer the time constant.
In contrast if there is current flowing in an inductor at the time of switch opening, then a very large voltage is generated upon opening because you can not instantaneously change the current thru an inductor. This voltage will be limited by something breaking down or some means of voltage limitation. For example a reverse biased diode across the inductor will provide a current path for the inductor current upon opening the switch.
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iwire:
A step change in voltage to an inductor does not cause a step change in current. Instantaneously you can not change the current in an inductor.
If I connect a battery thru a switch to a series L R circuit (inductance resistance), and the initial current thru the inductor at the time of switch closure is zero, then the current will be of the form (1-e^-tR/L). An exponential curve starting at 0 (1-e^0 = 1-1 = 0) and gradually rising to 1. The lower the resistance the longer the time constant.
In contrast if there is current flowing in an inductor at the time of switch opening, then a very large voltage is generated upon opening because you can not instantaneously change the current thru an inductor. This voltage will be limited by something breaking down or some means of voltage limitation. For example a reverse biased diode across the inductor will provide a current path for the inductor current upon opening the switch.
.
- Location
- Massachusetts
Gar, while I fully believe what your telling me, sadly I have no idea what your telling me. 
Was my post wrong? Was it right? I can't tell from your post.
What is your take on the reason for a specific dimmer for use with transformers?
My take was based on what I have read on the Internet but that is always suspect. :smile:
Was my post wrong? Was it right? I can't tell from your post.
What is your take on the reason for a specific dimmer for use with transformers?
My take was based on what I have read on the Internet but that is always suspect. :smile:
gar
Senior Member
- Location
- Ann Arbor, Michigan
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- EE
090424-1419 EST
Bob:
If a load has a series inductive component you can not have an instantaneous rise in current.
Transformers themselves have a inrush problem due to being driven into saturation as the result of the residual flux state from the last turn off. For a mechanical switch controlling the input to the transformer the resulting inrush current is random and can be very large. This is somewhat unrelated to the Triac dimmer application.
I will try to do an experiment with a Triac dimmer and a transformer and see if I can determine what may be the problem with such use.
.
Bob:
If a load has a series inductive component you can not have an instantaneous rise in current.
Transformers themselves have a inrush problem due to being driven into saturation as the result of the residual flux state from the last turn off. For a mechanical switch controlling the input to the transformer the resulting inrush current is random and can be very large. This is somewhat unrelated to the Triac dimmer application.
I will try to do an experiment with a Triac dimmer and a transformer and see if I can determine what may be the problem with such use.
.
- Location
- Chapel Hill, NC
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- Retired Electrical Contractor
Although I understood absolutely nothing of what was stated above as answers to your question I will tell you that there are some electronic transformers that do not need an electronic dimmer to operate.
Gar you need to throw that into the equation.
ELA
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- Electrical Test Engineer
I copied this out of a very long winded document:
"Transformer energy losses tend to worsen with increasing frequency. The skin effect within winding conductors reduces the available cross-sectional area for electron flow, thereby increasing effective resistance as the frequency goes up and creating more power lost through resistive dissipation. Magnetic core losses are also exaggerated with higher frequencies, eddy currents and hysteresis effects becoming more severe. For this reason, transformers of significant size are designed to operate efficiently in a limited range of frequencies. In most power distribution systems where the line frequency is very stable, one would think excessive frequency would never pose a problem. Unfortunately it does, in the form of harmonics created by nonlinear loads."
Could it be that not all transformers are not designed to handle the harmonics generated by the rapid rate of voltage change produced by the phase fired dimmer?
"Transformer energy losses tend to worsen with increasing frequency. The skin effect within winding conductors reduces the available cross-sectional area for electron flow, thereby increasing effective resistance as the frequency goes up and creating more power lost through resistive dissipation. Magnetic core losses are also exaggerated with higher frequencies, eddy currents and hysteresis effects becoming more severe. For this reason, transformers of significant size are designed to operate efficiently in a limited range of frequencies. In most power distribution systems where the line frequency is very stable, one would think excessive frequency would never pose a problem. Unfortunately it does, in the form of harmonics created by nonlinear loads."
Could it be that not all transformers are not designed to handle the harmonics generated by the rapid rate of voltage change produced by the phase fired dimmer?
gar
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- Ann Arbor, Michigan
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- EE
090425-1029 EST
The UK article on dimmers is a good reference.
My following experiments were performed with:
Signal Transformer A41-175-24, primaries in parallel, secondaries in series,
Lowest cost Lutron 2 wire dimmer,
Expensive Lutron 3 wire dimmer, SF-10P-IV,
1 ohm load resistor on transformer secondary at times.
Using the Lutron SF-10P the phase shift control works with the transformer loaded or unload. However, with the transformer unloaded and the dimmer turn on phase angle small, less than about 60 deg, the stored energy from the transformer causes abnormal operation. But clearly this dimmer provides sustained excitation to the Triac gate.
Under loaded conditions dimming characteristics appear to be good.
I have made no evaluation of temperature rise.
Using the inexpensive Lutron two wire dimmer, and I assume even using an expensive two wire dimmer, the results were: Weird with no load, and looked OK with load. With load possibly better than the SF-10P.
With no load the Triac turns on and off several times because there is insufficient holding current and the Triac gate does not have continuous excitation. There is obviously an internal time constant that determines the retrigger time.
There is a lot of loose usage of terms such as transformer. I suggest that it is poor usage to call any device that changes one voltage to another a transformer. We have over 100 years of use of the term "transformer" where the meaning is a passive inductive coupling device.
The term "electronic transformer" may be somewhat helpful, but what does that really mean? A DC to DC supply, A DC to AC supply, an AC to DC supply, a capacitive coupling device that uses no magnetic coupling, an optical device, and so on. Also note a motor generator can change voltage levels and the type of input or output.
What is an "electronic dimmer"?
.
The UK article on dimmers is a good reference.
My following experiments were performed with:
Signal Transformer A41-175-24, primaries in parallel, secondaries in series,
Lowest cost Lutron 2 wire dimmer,
Expensive Lutron 3 wire dimmer, SF-10P-IV,
1 ohm load resistor on transformer secondary at times.
Using the Lutron SF-10P the phase shift control works with the transformer loaded or unload. However, with the transformer unloaded and the dimmer turn on phase angle small, less than about 60 deg, the stored energy from the transformer causes abnormal operation. But clearly this dimmer provides sustained excitation to the Triac gate.
Under loaded conditions dimming characteristics appear to be good.
I have made no evaluation of temperature rise.
Using the inexpensive Lutron two wire dimmer, and I assume even using an expensive two wire dimmer, the results were: Weird with no load, and looked OK with load. With load possibly better than the SF-10P.
With no load the Triac turns on and off several times because there is insufficient holding current and the Triac gate does not have continuous excitation. There is obviously an internal time constant that determines the retrigger time.
There is a lot of loose usage of terms such as transformer. I suggest that it is poor usage to call any device that changes one voltage to another a transformer. We have over 100 years of use of the term "transformer" where the meaning is a passive inductive coupling device.
The term "electronic transformer" may be somewhat helpful, but what does that really mean? A DC to DC supply, A DC to AC supply, an AC to DC supply, a capacitive coupling device that uses no magnetic coupling, an optical device, and so on. Also note a motor generator can change voltage levels and the type of input or output.
What is an "electronic dimmer"?
.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
- Location
- Massachusetts
Dennis, I have only been talking about 'old school' magnetic transformers for low voltage lighting.
For electronic low voltage power supplies don't you have to use the specific dimmer unit they specify?
gar
Senior Member
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- Ann Arbor, Michigan
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- EE
090425-1445 EST
Dennis:
The Lutron SF may be classified for use with a magnetic fluorescent ballast that is designed for dimming, but it is a good, actually better, general purpose leading edge dimmer for use with resistive loads.
This dimmer has two features for fluorescent dimming. A power switch that controls two outputs. One output is a full voltage lead to provided continuous full voltage, stepped down in the ballast, for the lamp filaments. The second output is the leading edge phase shifted dimming voltage for the input to the ballast for lamp current.
To work effectively with the ballast inductive load it is necessary to provide continuous excitation to the Triac gate, at least until the holding current is exceeded. This is apparently done in this dimmer and in my opinion is the reason a neutral connection is required. Thus, I call this a three wire dimmer vs a two wire unit, because the third wire provides a means to power the gate at any phase angle.
The three wire capability allows this dimmer to work better in a normal incandescent lamp application. The full voltage power source, because of the neutral wire, allows the dimmer to operate at any turn on phase angle. However, Lutron does limit the range. What this means is that if I set the dimmer to a very low output level, turn power off, and back on that the lights will restart at this low level. What seems to be characteristic of the two wire dimmers is that with a low setting and reapplication of power there is no light. The two wire dimmer does not restart.
As I stated before every phase shift type dimmer is electronic. Therefore, electronic as a modifier of dimmer has nothing to do with the load. There should be some different name for a dimmer used for special loads, but not electronic, and there are lots of different special loads so there need to be a variety of different names for these.
As I pointed out above the SF dimmer may have been designed specifically to serve the needs of dimmable fluorescent fixtures that use a special magnetic ballast, but the same dimmer is useable in other applications. More specifically it may be useful for a variety of inductive and resistive loads.
.
Dennis:
The Lutron SF may be classified for use with a magnetic fluorescent ballast that is designed for dimming, but it is a good, actually better, general purpose leading edge dimmer for use with resistive loads.
This dimmer has two features for fluorescent dimming. A power switch that controls two outputs. One output is a full voltage lead to provided continuous full voltage, stepped down in the ballast, for the lamp filaments. The second output is the leading edge phase shifted dimming voltage for the input to the ballast for lamp current.
To work effectively with the ballast inductive load it is necessary to provide continuous excitation to the Triac gate, at least until the holding current is exceeded. This is apparently done in this dimmer and in my opinion is the reason a neutral connection is required. Thus, I call this a three wire dimmer vs a two wire unit, because the third wire provides a means to power the gate at any phase angle.
The three wire capability allows this dimmer to work better in a normal incandescent lamp application. The full voltage power source, because of the neutral wire, allows the dimmer to operate at any turn on phase angle. However, Lutron does limit the range. What this means is that if I set the dimmer to a very low output level, turn power off, and back on that the lights will restart at this low level. What seems to be characteristic of the two wire dimmers is that with a low setting and reapplication of power there is no light. The two wire dimmer does not restart.
As I stated before every phase shift type dimmer is electronic. Therefore, electronic as a modifier of dimmer has nothing to do with the load. There should be some different name for a dimmer used for special loads, but not electronic, and there are lots of different special loads so there need to be a variety of different names for these.
As I pointed out above the SF dimmer may have been designed specifically to serve the needs of dimmable fluorescent fixtures that use a special magnetic ballast, but the same dimmer is useable in other applications. More specifically it may be useful for a variety of inductive and resistive loads.
.
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