Refrigerators dissipate the heat extracted from the inside via a grid structure mounted at the rear side. When a refrigerator is located in a confined space, the rear side can get fairly hot owing to the limited convection.
This problem derates the overall efficiency of the refrigerator, since the motor is automatically switched on for longer periods when a considerable difference exists between the inside and outside temperature notably on hot days it often seems as if the motor is running continuously. The ventilation control described here can help economize on power consumption.
The circuit is simple, and does not require a detailed description. A simple DC supply is set up with Tri—C1. Temperature is measured with the aid of bridge circuit R1-R2-P1 and a NTC (negative temperature coefficient resistor). IC1 is a comparator which converts the bridge output into a gate current for triac Tri, which controls extractor fan M. Some hysteresis is provided by feedback resistor Ra. The triac is controlled with a direct gate current to avoid triggering problems arising from induced voltage peaks. The circuit is uncritical as regards construction. Be sure to observe the correct connection of the al and a2 terminals on the TIC206, else it remains trig- gered permanently. It should be noted that the circuit is dangerous to touch, as it is connected direct to the mains. It is possible to reduce the stand-by current by omitting Tri, and powering the circuit in parallel with the refrigerator motor. The NTC should be fitted near the grid at the rear side of the refrigerator. The triac can do with without a heat-sink.
This problem derates the overall efficiency of the refrigerator, since the motor is automatically switched on for longer periods when a considerable difference exists between the inside and outside temperature notably on hot days it often seems as if the motor is running continuously. The ventilation control described here can help economize on power consumption.
The circuit is simple, and does not require a detailed description. A simple DC supply is set up with Tri—C1. Temperature is measured with the aid of bridge circuit R1-R2-P1 and a NTC (negative temperature coefficient resistor). IC1 is a comparator which converts the bridge output into a gate current for triac Tri, which controls extractor fan M. Some hysteresis is provided by feedback resistor Ra. The triac is controlled with a direct gate current to avoid triggering problems arising from induced voltage peaks. The circuit is uncritical as regards construction. Be sure to observe the correct connection of the al and a2 terminals on the TIC206, else it remains trig- gered permanently. It should be noted that the circuit is dangerous to touch, as it is connected direct to the mains. It is possible to reduce the stand-by current by omitting Tri, and powering the circuit in parallel with the refrigerator motor. The NTC should be fitted near the grid at the rear side of the refrigerator. The triac can do with without a heat-sink.
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