02-04-2012, 11:52 AM
AUTOMATIC SPEED-CONTROLLER FOR FANS AND COOLERS
Automatic Speed Controller For Fans and Coolers.pdf (Size: 101.2 KB / Downloads: 121)
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.
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.
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.
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 value. 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.
Throughout the process, pin
11 of the IC3 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.
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.