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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Thermostat on the balcony. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers Very often, residents of city apartments have a problem with storing potatoes. In winter, there is no better place than on a balcony or loggia, even if there is a pantry. It is too warm in the pantry and even in the basement under a multi-storey building (many people have tested it on their own experience), and the potatoes begin to germinate quickly after storage. The balcony has a big advantage in this regard. However, here you can not do without a thermostat. I want to share with the readers of the Radio Amateur magazine a well-tested device. For the past five winters, except for replacing one or two light bulbs, it has not caused any trouble, reliably covering the tubers from frost outside the window of my apartment. I borrowed the electrical circuit from E. Babynin (see "M-K", 8/1985). The rest is "fantasy on a free theme." The thermostat is a box with double walls, the 40 mm space between them on the sides is filled with crushed foam from various packages. Good even sheets of foam are convenient to use to insulate the lid. They are glued in such a way that the foam of the cover goes inside the outer double side walls and rests on the inner walls. The inner walls are made lower in height than the outer ones in order to ensure a snug fit of the lid (see Fig. 1). If, nevertheless, a good compaction could not be achieved, it does not matter. In this case, foam rubber should be glued along the edges of the cover.
The inner bottom of the thermostat is freely inserted into the drawer. Several support bars 20 - 30 mm thick are nailed to the bottom from below. A pipe made of thin tin is attached to the bottom in the middle and from above, selected in such a way that it can accommodate electric light bulbs used as heating elements. If there is no tin at hand, cuttings of old ventilation pipes can come into play. In the bottom, under the pipe, drill several ventilation holes with a diameter of 8 ... 10 mm. After installing the bottom with the pipe attached to it, it must be ensured that the pipe is located approximately 20 mm below the inner walls of the box. This design of the thermostat allows the air heated in the pipe to freely circulate throughout the entire volume of our mini-storage, blowing over almost every tuber. The thermostat housing is easy to make from improvised materials, for example, from scraps of chipboard or thin boards. It is advisable to make the side outer walls with protrusions at the bottom in the form of legs so that the bottom does not come into contact with the cold concrete floor of your balcony. The dimensions of the thermostat are for reference, if desired, they can be reduced or increased, adapting to the size of the balcony and the volume of potatoes to be stored. The dimensions shown in fig. 1 thermostat - 1500x800x400.
On fig. 2 shows the electrical circuit of the thermostat thermostat. As a heating element, it uses two incandescent lamps (220V, 60 W), placed, as mentioned above, in a pipe. The heating element is connected to the V5 thyristor circuit. The thermal relay elements are powered by a stabilized power supply (V10, C1, R1). When the temperature sensor, made on the thermistor R4, is cooled, its resistance increases, and, consequently, the potential in the V9 base decreases until the transistors V8, V9 close. As soon as V8, V9 are closed, the current flowing through R2, R5 will open the transistor V6 and the thyristor V5 associated with it. The heater will work until the temperature in the area where the temperature sensor is located reaches a value at which the resistance decreases and the V8 V9 transistors open again. Transistor V6 and thyristor V5 will close and the process will repeat until dynamic equilibrium is established. The thermal relay can be assembled on any transistors with a sufficiently high (50) gain. Diodes D242 and thyristor KU202 are chosen to increase reliability. However, when replacing with other types of elements, it should be remembered that they are used for a forward current of 3A and a reverse voltage of 400 ... types of rectifier and thyristor diodes can not be installed on radiators. The thermistor must, as a precaution, be placed in a protective sheath (for example, in a tube from a used felt-tip pen). For the convenience of monitoring the operation of the thermostat, you can put a neon light after the fuse, which will indicate that the fuse is working. In addition, a shunt can be connected in series to the load circuit and a microammeter can be connected in parallel with it. The shunt resistance should be selected in such a way that when the thyristor is fully open, the microammeter needle deviates to the full scale. As a shunt For a microammeter of 100 µA and below, a piece of mounting wire of a suitable length may well be suitable. Then, by the magnitude of the deviation of the arrow of the microammeter, installed in any convenient place, it will be possible to judge the operation of the thermostat and the need to "replace a burnt out light bulb. The device does not require adjustment, except for setting the desired temperature. The temperature inside the thermostat should be 0 ... 4 C. This value is optimal for storing potatoes. Usually, with the specified dimensions of the thermostat, the fluctuations are 1 ... 2 C. The temperature is set by the resistor R7. The sensor is located on the surface of the potato. By the time this issue of the magazine comes out, it will already be spring in the yard, and the topic of storing potatoes may seem irrelevant to someone. Still, I would advise against throwing away the description of the thermostat. Autumn will come, and this simple design will help you out. Author: I.Belsky; Publication: N. Bolshakov, rf.atnn.ru
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