Tatung Rice Cooker

 The Tatung Rice Cooker is legendary.  It is durable, easily lasting twenty or thirty years.  Its construction is very simple and rugged, devoid of fancy electronics.  Currently it commands of a price of $200, several times that of the competitors.  But it often fails in a rather simple way: the power cord.  The power cord can break near the plug at the strain relief, at the entry point to the interior and the ring terminals inside.  Replacing the power cord can extend its life for many more years.  The repair is simple.  Once the bottom cover held by one screw is removed, the wiring is clearly shown.  Note that the fiberglass sleeves are placed over the power cord wire.  The insulation has to withstand high temperature, so choose the power cord with temperature rating of 105C.

The temperature control is achieved by a magnetic switch.  When  the lever is pushed, the magnets close the springy electric contacts to power the heating coil.  The heating coil is about 18 Ohms, which is about 800W at 120V, which is the rated power.  When the coil heats up, the resistance increases and the power settles down about 740W.  The coil is completely sealed to prevent oxidation. When the water evaporates, the temperature goes up rapidly and the magnet loses magnetic field and breaks the contact.  It can be verified that the switch does not close immediately afterwards.  When the temperature is below the magnet's Curie temperature, this demagnetization is reversible.  Because the temperature drops when the contact is broken, the magnet does not lose the magnetization permanently.  The Curie temperature is 450C for ferrite magnet.  The switch is open at about 220C and the magnet regains its magnetic field below 160C.

There is also a keep-warm switch, which adds a resistor (about 380 Ohms) to the coil and reduces the heating power (to about 35W).