Design of automatic controller for air-cooling and power-saving refrigerator

Practice has proved that using electric fans to dissipate heat from refrigerators is an effective way to save electricity. When the fan works continuously, the power consumption per month is only about 2 degrees. If the fan stops, the power consumption is only 0.7 degrees. The automatic controller introduced in this article, when the temperature rise of the refrigerator compressor reaches a predetermined value, the electric fan automatically supplies air to assist in heat dissipation, improve work efficiency, and prevent the refrigerator from starting frequently.
Working principle The working principle of the circuit of the device is shown in Figure 1 (click here to download the schematic diagram). It is mainly composed of a high-power switch integrated circuit IC2 and a thermistor Rt. When the temperature of the refrigerator compressor rises, the resistance of the thermistor Rt decreases, causing the voltage at point A of the circuit (i.e., the ① pin end of IC2) to rise to more than 1.5V. At this time, the drive tube inside IC2 8752 is turned on, and the relay J is excited and attracted, and the micro fan power is turned on to rotate and supply air. Once the temperature of the compressor drops, the resistance of thermistor Rt also increases, causing the voltage at point A to drop below 1.5V. At this time, the drive tube inside IC2 is cut off and the micro fan stops rotating. This not only cools the compressor, but also saves energy and extends the service life of the electric fan itself. Component selection and production See the table below for the component list.

serial number	name	model	quantity
R	Carbon Film Resistors	300Ω	1
RP	Trimmer resistor	2.2K	1
R	Thermistor	1K negative temperature coefficient	1
C1	Electrolytic Capacitors	220u/25V	1
VD1--VD5	Rectifier diode	IN4001	5
IC1	Three-terminal regulator	LM7806	1
IC2	High Power Switch IC	8752 or 8751	1
J	Relay	1A 6V any model	1
T	Power Transformer	12V 2--3W	1

The thermistor Rt is glued to the metal shell of the compressor with adhesive tape or strong heat-resistant adhesive. During debugging, use a cup of warm water (about 40℃), adjust RP to stop below body temperature, and then immerse the thermistor in hot water higher than human body temperature. At this time, be careful not to immerse the lead of the thermistor in water. When thermal equilibrium is reached (Rt rises to the hot water temperature), the motor is running, and the circuit is successfully debugged and can be put into use.