The revolution per minutes (rpm) of the DC motor is
measured by using the digital stroboscope tachometer every
time there are changes in output voltage. Fig. 5 shows the
speed of DC motor changed with the output voltage of the
driver. The results show that the driver manged to control the
motor speed in a linear manner. Fig 6 shows the changes of
the driver output power corresponding to various speed of the
motor. As the speed of motor increase, the output power will
remain closed to 5W. Which means that the driver output
power has the ability to remain constant throughout the speed
range. This characteristic enables the motor to turn slowly
without lossing power, which is very important in promoting
higher efficiency of solar tracking.
Current flow through the motor is measured under two
conditions, i.e. with load and without load. The shaft of the
DC motor is attached with weight of 130 grams as a load. Fig.
7 shows the relationship between the driver output current
and duty cycle when there is a load attached. The results
showed that the driver managed to control the output current
linearly, and therefore the torque by using PWM control
signal. This enables the solar tracking system to work
properly later on when there is a need to mount more solar
panels on it. When there is no load mounted on the motor, the
driver only consume current maximum at 0.05A throughout
the duty cycle range as shown in Fig. 8. Most of the time,
solar tracking system is installed in a remote rural area where
power grid is nowhere to be found. This will be a very