Rice Cooker Repair

URANUS RICE COOKER 350W 220V capacity 0.6 L

This article repair of rice cooker is from my good friend Beh. He is from Iran.

Recently I received above rice cooker from one of my friend and

He said the rice cooker is not working .By opening the back cover

I found just one mechanical switch and also the heating element and

Thermal fuse  SF 139 E  (S is type name of fuse 139 is operating temperature that fuse act) by testing with analog meter fuse showed that

Is open and by testing the circuit by a jumping wire i assured that the fuse

Is blown and by changing with same rate fuse 220 V 10 A rice cooker start to work  now rice cooker start to work but really I do not know the thermostat

Is good or not ?

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But what is a thermal fuse?:

A thermal fuse is a cutoff which uses a one-time fusible link. Unlike the thermal switch which automatically resets itself when the temperature drops, the thermal fuse is more like an electrical fuse: a single-use device that cannot be reset and must be replaced when it fails or is triggered. A thermal fuse is most useful when the overheating is a result of a rare occurrence, such as failure requiring repair (which would also replace the fuse) or replacement at the end of service life.

One mechanism is a small meltable pellet that holds down a spring. When the pellet melts, the spring is released, separating the contacts and breaking the circuit. The NEC Sefuse SF/E series, Microtemp G4A series and Elmwood D series, for example, use pellets that contain Copper, Beryllium, and Silver.

Thermal fuses are usually found in heat-producing electrical appliances such as coffeemakers and hair dryers. They function as safety devices to disconnect the current to the heating element in case of a malfunction (such as a defective thermostat) that would otherwise allow the temperature to rise to dangerous levels, possibly starting a fire.

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Unlike electrical fuses or circuit breakers, thermal fuses only react to excessive temperature, not excessive current, unless the excessive current is sufficient to cause the thermal fuse itself to heat up to the trigger temperature. Such an arrangement may be found in a surge protector. The thermal fuses are wired in series with the varistors; when the varistors conduct, the fuse heats up and fails, which eliminates the risk of fire.

In this unit varistor is not employed.