A simple heat stabilizer for a vegetable store. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers
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The offered thermostabilizer allows to maintain the set temperature within 0...+25°С. Temperature maintenance accuracy - 1...2 degrees. The maximum load power is 600 watts.
The scheme of the device is shown in fig. one.
Transformer T1 lowers the mains voltage to 12 ... 15 V. Elements R1 and VD2 form a parametric voltage stabilizer. The temperature sensor is thermistor R2. Incandescent lamps EL1 and EL2 (each 300 W) act as a heater. Capacitor C2 is designed to extinguish the spark on the relay contacts.
The desired temperature is set by a variable resistor R3. In the initial state, when the temperature has not reached the set value, the resistance of the thermistor R2 placed inside the vegetable store is large. As a result, transistor VT1 is closed, relay K1 is de-energized and its contacts are in the position shown in the diagram. Lamps EL1 and EL2 are on and provide heat. As the vegetable store warms up, the resistance of the thermistor R2 decreases, as a result of which the voltage at the base of the transistor VT1 increases.
When the temperature inside the vegetable store rises to a predetermined value, transistor VT1 opens, relay K1 is activated and its contacts break the lamp supply circuit. When the air cools, the resistance of the thermistor R2 increases again, the transistor VT1 closes and the heating process resumes.
The diode assembly VD1 can be of the KTS405, KTS402 series with indices B-E. Transistor VT1 - KT827 or KT829 series with any letter index. Zener diode VD2 can be replaced by KS139A or KS147A. Relay K1 - RES-6, passport RFO 452.104-01.
All parts of the device (except for the thermistor and lamps) are best mounted on the board and placed in a plastic box. If the length of the cable with which the thermistor is connected exceeds 20 cm, it is advisable to use a shielded wire.
If desired, you can use an electric heater with a power of up to 2 kW (Fig. 2).
It is desirable to shunt the winding of relay K1 with a diode. Its cathode must be connected to the resistor R1, and the anode to the collector of the transistor VT1. Together with the RES-6 relay, it is better to use a tubular heating element (TEH). When using lamps, it is desirable to use a more powerful relay.
Author: E.Natnenkov
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