The induction cooker is one of the commonly used home appliances and kitchen utensils closely related to our lives. However, the induction cooker is sometimes used improperly, or after a long time of use, it is inevitable that there will be such thorny and difficult problems. A few days ago, the Midea home induction cooker broke down. I took it to the maintenance department to disassemble and detect the problem. My stove smelled too much oily smoke when cooking, and I didn’t pay attention to the air circulation in the kitchen. The internal circuit board of the induction cooker was corroded over time. Excessive oily fume stains caused the display panel to not work and cannot be turned on. Later, the maintenance master replaced a main circuit board to resume normal work. It also spent a lot of money to buy chestnuts with life experience, indicating that the daily maintenance work of the induction cooker is also a very important link.
The induction cooker is heated by the electromagnetic field, and the iron core will heat up when the power frequency transformer in the household appliance is working. The PTC heater core is neither connected to the primary winding nor to the secondary winding. How can it generate heat? Let’s take a look at the picture below with a question:
The structure diagram of a common power transformer is shown in the figure above. When the coil is energized with alternating current, an alternating magnetic field is generated in the coil. Each piece of silicon steel sheet in the transformer has magnetic lines of force passing through. Due to the change of magnetic field intensity, the number of magnetic lines (magnetic flux) passing through each piece of silicon steel sheet changes. According to Lenz's law, it will be generated inside each piece of silicon steel sheet. Close the vortex-shaped induced current (the current direction is the current direction at a certain moment) to prevent the change of magnetic flux. This induced current is called eddy current, or eddy current for short. The eddy current flows in each silicon steel sheet. Because the current has a thermal effect, the silicon steel sheet heats up and the temperature rises. The phenomenon that eddy currents convert electrical energy into heat energy through metal is called the thermal effect of eddy currents.
Although the heating effect of eddy current will have an adverse effect on electrical equipment, it can be applied to heating technology, which is called electromagnetic heating technology.
In the case of induction cooker without heating for a period of time, the usual cause may be the overcurrent of the main circuit or the overvoltage protection of the power tube c. (You can check the power in the main circuit, whether there is leakage in the full bridge; whether there is a problem with the current of the potentiometer VR1, and whether the power supply voltages of 5V, 18V, and 300V are normal in the standby state)
First, you can check if the induction cooker is heated for a period of time without heating. This situation is intelligent (computer control mode) or manual; if it is intelligent control, it means that the selected induction cooker mode is wrong, just change another cooking mode. If it is manual, it may be that the thermal conductive silicone grease on the temperature sensor on the coil disk is less, and it will be better to add some thermal conductive silicone grease. If adding thermal grease does not work, it is a problem in the main class.
High voltage capacitors and high voltage resistors on the motherboard are broken. This problem can also occur. If there is no problem on the motherboard, it may also be the display board, but it is rare that the display board is broken.
In addition, check the two thermistors on the lower coil, one on the IGBT tube and the other in the middle of the coil disk (the resistor on the disk is coated with white thermal grease). Check whether the synchronous large resistance value changes when the resistance is working, and whether the working voltage of the two sections of the resistance is normal. Sometimes, unstable voltage can also cause the induction cooker to not heat up.
Observe whether there is any looseness in the internal plugs of the induction cooker. You can unplug the two plugs of the magnetron and test the primary line voltage of the transformer if it is energized. If it is unstable, you can cut off the power. Use pliers to pull out the plugs in turn to check whether there is any looseness. , The micro switch can also be measured with a meter. PTC heater
The intermittent heating failure of the induction cooker involves many failure points, and it is more troublesome to repair. According to experience, it is simple and feasible to carefully observe the current size change to judge the fault range:
1. When the current jumps in the range of 0---7A. Should focus on checking whether the large resistance of the synchronization circuit has changed, and whether the voltages at the two sampling terminals of the synchronization circuit are normal.
2. When the current jumps in the range of 0---4A. Should focus on the current detection circuit components, such as current transformer (new furnace constantan wire and dual operational amplifier circuit), adjustable resistors, diodes, resistance-capacitance components and single-chip circuit.
4. The heating of small gear is normal, and heating of large gear is intermittent. You can check 300V and filter capacitor first, and check whether the capacity of 2F anti-interference capacitor is reduced. You can try it with 3.3F capacitor. However, due to the small diameter of the power supply lead-in wire or poor contact of the socket, the failure caused by the use of pots and utensils that does not meet the requirements cannot be ignored.
1. The induction cooker has a certain low-frequency electromagnetic radiation. Do not operate with magnetic cards (such as bank cards) and watches that cannot be anti-magnetic to avoid magnetization, demagnetization or damage.
2. Although it has not been proved that a small amount of low-frequency radiation is harmful or harmless to the human body, pregnant women and children should not use the induction cooker, just in case.
3. The distance between the operator and the induction cooker should not be less than 0.5 meters, and do not stand by the induction cooker for a long time to reduce electromagnetic radiation and ensure safety.
4. The induction cooker uses a magnetic field to induce eddy current heating, that is, a magnetic field is generated by passing a current through a coil. When the magnetic field lines in the magnetic field pass through the bottom of the iron pot, the magnetic field lines are cut, thereby generating countless small eddy currents, making the iron atoms in the iron pot itself It rotates at a high speed and generates collision, friction, and heat to directly heat the food in the pot. In other words, the PTC heater is heated by the hysteresis effect of the ferromagnetic body in the alternating magnetic field. Therefore, the pot should use an iron pot instead of a ceramic pot. If you use aluminum pots, copper pots and other metal pots, their heating efficiency is also very low, and basically cannot be used.