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Automatic speed-controller for fans and coolers mini project
can be seen that initially the fan shall get AC supply directly, and so
it shall run at top speed. When output Q2 becomes high and Q1 becomes
low, relay RL1 is turned ‘off’ and relay RL2 is switched ‘on’. The fan
gets AC through a resistance and its speed drops to medium. This
continues until output Q4 is high. When Q4 goes low and Q5 goes high,
relay RL2 is switched ‘off’ and relay RL3 is activated. The fan now runs
at low speed.
process, pin 11 of the IC is low, so T4 is cut off, thus keeping T5 in
saturation and RL4 ‘on’. At the end of the cycle, when pin 11 (Q9)
becomes high, T4 gets saturated and T5 is cut off. RL4 is switched
‘off’, thus switching ‘off’ the fan/cooler.Using the circuit described
above, the fan shall run at high speed for a comparatively lesser time
when either of Q0 or Q1 output is high. At medium speed, it will run for
a moderate time period when any of three outputs Q2 through Q4 is high,
while at low speed, it will run for a much longer time period when any
of the four outputs Q5 through Q8 is high.
If one wishes, one can
make the fan run at the three speeds for an equal amount of time by
connecting three decimal decoded outputs of IC3 to each of the
transistors T1 to T3. One can also get more than three speeds by using
an additional relay, transistor, and associated components, and
connecting one or more outputs of IC3 to it.
In the motors used in certain coolers there are separate windings for
separate speeds. Such coolers do not use a rheostat type speed
regulator. The method of connection of this device to such coolers is
given in Fig.The resistors in Figs are the tapped resistors, similar to
those used in manually controlled fan-speed regulators. Alternatively,
wire-wound resistors of suitable wattage and resistance can be used.
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