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Here in this circuit, We have the load connected to a diac and triac circuit along with a variable resistance and a capacitor. enter image description here

When the circuit operation begins initially, the energy is stored in the capacitor until it reached the required threshold value to activate the diac ( D1). Once that happens, the diac ( which acts as the voltage regulator) generates the required gate voltage to activate the triac which is the main component contributing to the voltage regulation across the load.

The variable rheostat is the pointer regulator under manual control. By adjusting the rheotstat, we can control the charge in the capacitor which can further control the voltage drop across the load. And this regulation in voltage finally leads to change in the brightness of the bulb. Hence, when not doing any heavy activity like reading or writing, the bulb or tube light dimness can be attained and hence can lead to less power consumption. Also, if we use a purely resistive circuit for this purpose ( using a variable resistance or rheostat), the ohmic resistance of the circuit increases. Hence, using triac and diac switching devices help in reducing the ohmic losses and increase the efficiency of the circuit.

I wanted to know how efficient this concept would be in power saving. Will it contribute to a substantial level in reduction of power consumption if applied to an entire house?


Link to the circuit: http://www.eleccircuit.com/wp-content/uploads/2010/09/light-ac-dimmer-120watt.jpg

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  • \$\begingroup\$ You know that these phase fired "dimmer" circuits are found virtually everywhere? Light dimmers, vacuum cleaners, power drills, almost anything that needs cheap power control. Asking about whether it would be a good and efficient thing to use everywhere seems a few decades too late... \$\endgroup\$ – PlasmaHH Dec 15 '15 at 11:02
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    \$\begingroup\$ Turn all the lights off, then the energy saving is at most. \$\endgroup\$ – Marko Buršič Dec 15 '15 at 11:13
  • \$\begingroup\$ Of course that is an option but if we need to do tasks that do not require so much light as required for reading and other activities for example if the room is currently being used to simply sit and relax and engage in conversation, turning off the light might not be the most desirable approach and there wouldn't be any need to use a bulb with the rated brightness ( power?) \$\endgroup\$ – S_Learner Dec 15 '15 at 18:59
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It is a very standard dimmer circuit.

enter image description here

When used properly (with the right kind of load) it is very efficient as it quickly switches on and off. It is mainly usable for resistive loads which means oldfashioned lighbulbs. It is less suitable or even unsuitable for most LED lights, fluorescent lamps, electric motors. Electric motors can be dimmed but you need a slighlty more complex dimmer.

If you want to lower the power consumption investing in this circuits for only your oldfashioned light bulbs (which is about the only usable application) is counter productive. It is cheaper to replace the lightbulb with a lower rated one or even better, a LED based lightbulb.

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  • \$\begingroup\$ Aaaggh! Avoid 4 way joins on a circuit diagram, use 3 way joins and stagger them please! \$\endgroup\$ – Neil_UK Dec 15 '15 at 11:43
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    \$\begingroup\$ Keep your pants on ;-) And I didn't draw that. As long as it is clear, there's a dot in the middle so it is clear that all are connected. \$\endgroup\$ – Bimpelrekkie Dec 15 '15 at 12:30
  • \$\begingroup\$ Nah, 4 way dots must die! I've seen some circuit simulators where the schematic 4 way dots were light green instead of black, which means they disappear on a monochrome print-out. Hand-drawn back-of-envelope schematics suffer from biro splodges, and scan/print copies can lose or gain dots with little provocation. It's something I feel more strongly about than the appropriate use of apostrophes when constructing the possessive its. \$\endgroup\$ – Neil_UK Dec 15 '15 at 12:37
  • \$\begingroup\$ Although I fully agree with you and never draw it like that myself it will pop up now and then so I choose to ignore it :-) \$\endgroup\$ – Bimpelrekkie Dec 15 '15 at 12:41
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    \$\begingroup\$ sorry, my bad, each time I've opened this Q/A, the OP's image has failed to render, until now, so I thought yours was the first use. \$\endgroup\$ – Neil_UK Dec 15 '15 at 15:06
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Off course the dimmed lamp will use less power than the full lamp .OK you could do your circuit from the internet which must be good.You will probably find the dual time constant dimmer more stable at low light levels .If you live close to a street transformer you may blow the dimmer when the bulb blows which may defeat the proposed savings .I have seen series paralell switching of two lightbulbs ,This might be for you .Remember that a dimmed lightbulb is much less efficient than a undimmed one because dimming means relatively more invisible infrared radiation or heat which if you are in a hot country means more aircon power draw .If you could switch between a big bulb and a little bulb that would save more power .Better still use LEDs ,they will pull a quarter of the power that an incandescant uses and they are very dimmable .In fact LEDs become slightly more efficient at lower currents .

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Applying this circuit to an entire house would be problematic in three ways.

  1. The size of triac needed would very large and expensive.
  2. 220v circuits in a 110v house would need special attention because they use two hot legs.
  3. There are many many electronics that don't like this kind of dimming such as refrigerators, TVs, computers, florescent lights, microwaves, etc... Resistive loads like this dimming like incandescent light bulbs. There are some compact florescent lights that like it. There are some motors that like it. The like it list is far shorter then the don't like it list.
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    \$\begingroup\$ I have some more: 4) due to the switching of the TRIAC there will be A LOT of electrical switching noise in your whole house. Your neighbors might also suffer from that. 5) The electricity company will not like you loading the mains with such a device. A few lamps OK but not your whole house. \$\endgroup\$ – Bimpelrekkie Dec 15 '15 at 12:38
  • \$\begingroup\$ So what alternative should I use if I want to make this circuit work keeping in mind efficiency and cost reduction? \$\endgroup\$ – S_Learner Dec 15 '15 at 19:06

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