washing machines usually employ
a single-phase motor. In semiautomatic washing machines, a
purely mechanical switch controls the timing and direction of the motor. These
switches are costly and wear out easily. in the paper a controller for single-phase
motors of washing machines (Fig. 1) that efficiently replaces its mechanical equivalent. Basically, a single-phase motor requires a master timer, which decides the time for which the motor should keep rotating (washing time), and a spin direction controller, which stops the motor for 3 seconds after every 10 seconds and
then resumes rotation in opposite direction.
The direction of rotation can be controlled as shown in Fig. 2. When switch
S1 is in position A, coil L1 of the motor receives the current directly, whereas coil
L2 receives the current with a phase shift due to capacitor C. So the rotor rotates in clockwise direction (see Fig. 2(a)). When switch S1 is in position B, the reverse happens and the rotor rotates in anti-clock- wise direction (see Fig. 2(b)). Thus switch S1 can change the rotation direction.
The motor cannot be reversed instantly. It needs a brief pause between switch-
ing directions, or else it may get damaged. For this purpose, another spin direction control timer (IC2) is employed. It is realised with an IC 555. This timer
gives an alternate ‘on’ and ‘off’ time duration of 10
seconds and 3 seconds, respectively. So after every l0 seconds of running (either
in clockwise or anticlock wise direction), the motor
stops for a brief duration of 3 seconds. The values of
R3 and R4 are calculated accordingly.
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