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Probably the most easy and simple way to obtain speed control of fans is by connecting a series hi-watt tapped resistor with the load (the fan). The ordinary bulky types of ceiling fan dimmer switch incorporate the above method to keep the manufacturing costs to the minimum. But this principle of obtaining speed control comes with few of the following serious drawbacks:
- The series resistor gets heated up quickly. The heat is inversely proportional to the speed of the ceiling fan.
- Lots of energy is thus wasted in the form of heat.
- Such regulators are not long lasting and become faulty very often.
- The outer cover gets black and corroded due to excessive heat release of the resistor.
An interesting and efficient way of making a dimmer switch for ceiling fan is by using an auto-transformer. But these are too costly, cumbersome, and heavy, and they absolutely do not fit in the present competitive world.
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Phase Control through Triacs Looks More Feasible
The electronic version of speed control used in modern ceiling fan dimmer switches is much smarter since the following flawless features are achieved through them.
- No heat release means less power loss and efficiency near to cent percent.
- The speed control is smooth and continuously variable.
- Small and compact in size, it easily fits on any electrical board and comes with aesthetic looks.
Phase control is a technology where the alternating voltage is "cut" or "chopped" into discrete sections to obtain an effective speed control of the ceiling fans. This "chopping" is done by the means of a fast electronic switch or the triac.
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How Phase Control Takes Place
Referring to the figure we find that an AC cycle or phase alternates from its positive peak to the negative peak, crossing the zero mark in between. This happens normally 50 times per second in our domestic AC mains line.
In an electronic dimmer switch for ceiling fan the power control is achieved through the following simple operations:
- The speed control knob protruding out of a ceiling fan dimmer switch is actually a potentiometer or a variable resistor.
- Every time we move or rotate this knob the internal setting of the variable resistor is changed.
- As per this setting, a capacitor is kept charged to a particular point of the phase rising to its positive or negative peak.
- As long as the capacitor remains charged, the triac in the circuit remains switched ON and keeps the fan operative.
- Now as the phase approaches the zero crossing point, the capacitor discharges, turning OFF the triac as well as the fan.
- Thus only for a section of the phase the triac and the fan stays switched ON.
- This operative section of the phase can be increased or decreased by varying the setting of the knob or the variable resistor and in this way the speed control in a ceiling fan dimmer switch becomes feasible.
Image Courtesy: http://www.sprags.com/