Examples of maintenance methods of old-fashioned rice cookers

First, the working principle of rice cookers

The rice cooker heats the pot with a heating plate at the bottom. There is a round hole in the center of the heating plate, and a temperature limiter (temperature limiter) is embedded in the hole.

1) When the cooking button is pressed, the crossbar of the button drives the permanent magnet in the temperature limiter to attract the thermal ferrite upward. At the same time, the changeover switch turns on the power supply of the heating plate. When the cooking red light is on, the rice cooker enters the cooking state, and the circuit is shown in the following figure:

2) When the rice in the pot boils, the water gradually decreases. When the temperature in the pot rises to 103℃, the heat-sensitive ferrite in the temperature limiter loses its magnetism, and the permanent magnet turns off the change-over switch and cuts off the power supply of the heating plate under the action of the spring. At the same time, the insulation resistor is connected with the insulation circuit, so that the temperature of the rice cooker is kept at about 70 degrees. At this point, the circuit is shown in the following figure:

Second, the common faults and troubleshooting methods

1) When the plug is plugged into the power supply, the indicator light does not light up and cannot be heated.

According to the previous circuit principle, after the plug is plugged in, one of the indicator lights of the rice cooker should be on whether the cooking key is pressed or not. The indicator light is not on, indicating that the power supply circuit of the rice cooker is open. In the circuit of the rice cooker, a safety resistor is usually set. When the safety resistor of the rice cooker overtemperature due to long heating time or poor terminal contact, the safety resistor will fuse quickly, thus disconnecting the power supply circuit of the rice cooker. Troubleshooting: Replace the safety resistor. At the same time, carefully clean up the oxidation corrosion layer of the terminal and bolt to expose the metallic luster of the terminal and bolt to ensure good contact.

2) Jump to the heat preservation state before the rice is cooked.

The normal cooking temperature of the rice cooker is 103 degrees. If this temperature is exceeded, the rice cooker will automatically enter the heat preservation state. When the rice is not cooked, it jumps to the heat preservation state, which is generally caused by the following reasons:

(1) Whether there are sundries between the bottom (liner) and the heating plate or whether the bottom is deformed. Debris or deformation at the bottom of the pot will increase the distance between the permanent magnet and the heat-sensitive ferrite in the temperature limiter, which will make it impossible to attract them completely.

In this way, with the increase of the temperature of the heating plate, when the heat-sensitive ferrite in the temperature limiter does not completely lose its magnetism, the permanent magnet is separated from the heat-sensitive ferrite under the action of the spring, and the changeover switch is turned off, thus stopping the heating process of the rice cooker in advance and jumping to the heat preservation state. Troubleshooting method: clean the sundries on the bottom of the pot and the heating plate. The deformation of the pot bottom can be leveled according to the contour of the surface of the heating plate, so that the pot bottom and the surface of the heating plate are evenly attached. Especially, the middle part of the pot bottom must not protrude upward to ensure that the permanent magnet and ferrite in the temperature limiter are completely attracted.

(2) Temperature limiter aging

The temperature limiter is a kind of temperature switch based on the loss of excitation of heat-sensitive ferrite at a certain temperature. In normal use, when the temperature of the heat-sensitive ferrite is higher than 103 degrees (when all the water in the pot is boiled dry), the magnetism of the heat-sensitive ferrite will completely disappear (no longer attracted by the permanent magnet), and this temperature is called "Curie point temperature". After the magnetism of the heat-sensitive ferrite disappears, the permanent magnet in the temperature limiter resets the temperature limiter under the action of the spring, and the rice cooker turns to the heat preservation state at this time. After the thermal ferrite of the temperature limiter is aged, the "Curie point temperature" changes, and there will be a fault phenomenon that the temperature limiter acts before it reaches 103 degrees. To eliminate this fault, only the "temperature limiter" can be replaced.

(3) The change-over switch has poor contact or the distance between the upper contact and the elastic sheet changes.

The change-over switch has poor contact. You can grind the contacts with sandpaper to make them contact well. The distance between the upper contact and the elastic sheet is variable, so try to adjust it up and down with needle-nosed pliers, so that when the cooking button is pressed, the contacts can be in close contact. When the button jumps, the contacts can be separated.

Summary: Starting from the working principle of the rice cooker, the common faults of the rice cooker are analyzed in detail. In order to eliminate the fault in time, it is necessary to analyze a certain fault phenomenon in detail, and then carry out targeted operations in combination with the causes of these faults to avoid the expansion of the fault.

After troubleshooting, a small amount of water should be put in the pot for power-on test. If the water in the pot is boiled, the button jumps, indicating that the fault has been eliminated. Otherwise, it is necessary to further adjust the bottom of the pot or the change-over switch.

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