Motor-Driven Appliances: Fans, Mixers, Grinders and Washing Machines
Motor-Driven Appliances: Fans, Mixers, Grinders and Washing Machines
This domain tests single-phase motor starting, speed control and the mechanical and electrical faults in common appliances.
Core rules and concepts
- A single-phase induction motor is not self-starting. A capacitor creates a phase difference between windings, producing starting torque. A ceiling fan uses a permanent-split capacitor motor, typically 2.25 µF at 440 V, with a tapped winding for three speeds.
- Mixers and grinders use a universal motor with carbon brushes; it runs on AC or DC and gives high speed. Sparking at brushes, worn brushes and worn bearings are common faults.
- Washing machines use a capacitor-start motor, timer or controller, water inlet solenoid valve, pressure switch, drain pump and door interlock. Semi-automatic machines have separate wash and spin timers.
- Symptoms: a fan hums but does not turn - check capacitor, bearing and winding; a mixer runs slow - check brushes, load and winding; a washing machine does not fill - check tap, inlet filter, solenoid and pressure switch.
Worked example
A ceiling fan hums but the blades do not rotate. Measure the capacitor: if it is open or bulged, replace it with the same capacitance and voltage rating. If the capacitor is good, check that the shaft turns freely; a stiff bearing prevents starting. If both are good, measure winding resistance; an open winding needs rewinding. Reasoning: start from the cheapest, most common cause and work toward the motor.
Traps that cost marks
- Fitting a 2.25 µF capacitor where 4 µF is specified.
- Using a capacitor with too low a voltage rating.
- Running a mixer without load for long periods.
- Ignoring water leaks into a washing-machine motor.