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Automatic
Speed-Controller for Fans and Coolers
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| During
summer nights, the temperature is initially quite high.
As time passes, the temperature starts dropping. Also,
after a person falls asleep, the metabolic rate of one’s
body decreases. Thus, initially the fan/cooler needs to
be run at full speed. As time passes, one has to get up
again and again to adjust the speed of the fan or the
cooler. |
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The
device presented here makes the fan run at full speed
for a predetermined time. The speed is decreased to
medium after some time, and to slow later on. After
a period of about eight hours, the fan/cooler is switched
off.
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| Fig.
1 shows the circuit diagram of the system. IC1 (555) is
used as an astable multivibrator to generate clock pulses.
The pulses are fed to decade dividers/counters formed
by IC2 and IC3. These ICs act as divide-by-10 and divide-by-9
counters, respectively. The values of capacitor C1 and
resistors R1 and R2 are so adjusted that the final output
of IC3 goes high after about eight hours. |
| The
first two outputs of IC3 (Q0 and Q1) are connected (ORed)
via diodes D1 and D2 to the base of transistor T1. Initially
output Q0 is high and therefore relay RL1 is energised.
It remains energised when Q1 becomes high. The method
of connecting the gadget to the fan/cooler is given in
Figs 3 and 4. |
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It
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.
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| Throughout
the 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. 4. |
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The
resistors in Figs 2 and 3 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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