HOW TO REPAIR AND DIAGNOSE A RICE COOKER MACHINE

RICE COOKER

A rice cooker is an electrical machine which is use purposely for cooking rice. A simple rice cooker monitors the boiling point of water and take an action based on a set point.

HOW IT WORKS

A simple rice cooker  has a thermal fuse, a heating elements, two temperature sensors, and two light indicators(for cook and warm)

1.Thermal Fuse

Thermal fuse is a heat-sensitive device designed to protect electrical appliances and equipment from overheating and burns. it open circuit when the temperature exceed  the rated operating temperature.

how to diagnose the the thermal fuse

Use a multimeter to test for continuity

2. Magnetic Temperature Switch

It is use in the cook stage of the rice cooker.

The user press the switch to the cook state and the magnet hold it in that state until the temperature reaches or exceed the set boiling point where the magnet then demagnetize at that temperature and open the circuit thus returning the switch state back to warm.

3. Positive Temperature Coefficient (PTC) Thermistor Sensor

It is use in the warm stage of the rice cooker.

In the warm state; the thermistor (positive  temperature coefficient meaning it's resistance increases with temperature ) monitors the temperature of the heater and if it is high, its resistance increases thereby decreasing the  amount of current flowing through the heater hence the heat reduces and vice versa.

4. Heating Element

The heating element converts electrical energy into heats(it act as a resistive load which dissipate heat as current flows through )
the resistance of the heating can be calculated given the power rating of the rice cooker $P_{rated}$ and voltage rating \(V_{rated}\), the resistance of the heater can be calculated as: \[R=\frac{V_{rated}^2}{P_{rated}}\]

The rice cooker shown here \(P_{rated}=500 W\) and \(V_{rated}=220V\) so the resistance of this cooker will be \(R=\frac{220^2}{500}\) which is \(R=96.8\text{ Ohms}\)

If the resistance measured deviate more from the calculated value that means the heating element is Faulty.