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Refrigerator thermostat substitute device

Article Source:Thermal protectorAuthor:YaxunPopularity:Published time:2019-10-08 16:09

When the thermostat of the refrigerator is damaged, if it is difficult to configure a new thermostat. The electronic temperature controller introduced in this paper can be used for emergency use.
Keywords: Replacement refrigerator thermostat means

working principle
Circuit operation diagram of refrigerator thermostat substitute device
It uses a time base integrated circuit NE555 as a loop timing controller. When the power is turned on, since the pins 2 and 6 of IC1 are low, the IC1 trigger is set and its 3 pin is high. At this time, the relay J is energized, its normally closed contact j1 is disconnected, and R5 does not function. At the same time, the normally open contact j2 is closed, and the refrigerator is powered to start working and cooling. At this time, since the pin 3 of IC1 is in the high state, the diode VD6 is turned on, and the current is charged to the C1 through the resistors R1 and R2, as time passes. When the voltage across C1 rises to 2/3 of the power supply voltage, IC1 automatically resets, its 3 pin becomes low level, the corresponding relay J also loses power and the refrigerator stops working. After stopping the operation, since IC1's pin 3 is low, j1 is turned on for R5. Due to the R5 access, the threshold voltage of IC1 is not 1/3 of the power supply voltage, but 1/2 of the IC15 pin voltage. At this time, C1 is discharged through R3, R4 and IC1 internal discharge tube. When the voltage placed on C1 drops to about 1V, IC1 is re-turned and set, that is, IC1's 3 pin turns high again. Therefore, since the R5 access can make the smaller R3 and R4 resistance values ​​obtain a longer delay, the first and subsequent charging time differences can also be reduced.
Therefore, since the R5 access can make the smaller R3 and R4 resistance values obtain a longer delay, the first and subsequent charging time differences can also be reduced. According to the value of the schematic diagram, proper adjustment of R2 and R3 can change the startup and shutdown times of the refrigerator to about 5-15 minutes. In order to extend the shutdown time of the refrigerator, the resistance of R5 can also be appropriately reduced.

Component selection and production
The list of components is shown in the table below.

Numbering Name Model Quantity
470K 1
R2 Trimmer resistor 1.5M 1
R3 Trimmer resistor 680K 1
R4 resistance 360K 1
R5 resistance 1.2K 1
C1 Electrolytic capacitor 470u/16V 1
C2 Polyester capacitor 0.04u 1
C3、C4 Electrolytic capacitor 220u/25V 2
VD1-VD6 rectifier diode IN4001 6
IC1 Three-terminal regulator IC LM7812 1
IC2 Time base circuit IC NE555 1
J Relay 15A 12V 如:JCZ-22F 1
T Power Transformers power≥5W 1

In use, it is necessary to adjust the resistance values of R2 and R3 according to the changes of different seasons so that the minimum temperature and the maximum temperature of the refrigerator can meet the required requirements. Generally, the difference between the highest temperature and the lowest temperature in the refrigerator should be controlled between 6-10 °C. The hourly opening and closing ratio does not exceed 8, and the time for each downtime should be adjusted to not less than 5 minutes.
After the circuit is debugged, it can be installed in a plastic case, and the socket CZ can be additionally installed.