Power Off Timer

This simple device automatically disables the power supply after a predetermined period of time, For example, it can protect the battery from overcharging. timer Features

  • Relay response time range: 30 seconds … 10 hours
  • switching: relay
  • the load on the relay contact: 8BUT / 230AT
  • power supply: 12 In DC

circuit Description

Schematic load off timer circuit is shown in Figure 1.

rice. 1

It was made with cheap integrated circuit CD4060. The chip contains in its composition and divisors ready oscillator frequency signal from the internal oscillator. potentiometer P1, Resistors R2 and R3 and capacitor C4 define the period signals generated. This is expressed by the formula: T = 2,2 C4 × × (P1 + R3). For values ​​of the circuit elements and the potentiometer P1, established by half, we obtain the following approximate duration of the signal on separate outputs US1 (from Q1 … Q14): 35 with; 70 with; 140 with; 4,5 min; 9 min; 19 min; 38 min; 2,5 o'clock; 5 hours; 10 hours. The selection is made by jumper. The countdown begins after contact closure S1 button. At the same time CD4060 chip restarts, To make sure, that counting begins with 0. Further power backup is performed using a pair of relay contacts PK1. Its coil is supplied through the transistor T1, which is open only, when system selected output Low. After the countdown, and the settings of the selected output transistor is closed, and the relay shuts off power to the circuit and the controlled device. idle switch is not receiving power from the power source, the operation of which is indicated at LED 1. J2 connector is supplied in, and J1 connector is considered as an ordinary switch and in series with disconnecting device.

Installation and setup

The device is assembled the two-way board size 81 mm × 32 mm. The assembled board is shown in Figure 2. It is desirable to use a landing slot for the integrated circuit. Contact JP1 connector, They can be short-circuited by a jumper, in the model board, or connected to the 10-position rotary switch, wherein the common connector lead to a resistor R4. Start the timer is not complicated. After connecting power source (ca.. 12 AT, not necessarily stabilized, current of at least 50 mA) ready for operation. Adjust only frequency signal generator. This is done with the potentiometer P1. Before adjusting the slider in the middle position. Then, using a stopwatch or timer with a second hand, make sure, that the set time (as possible to eliminate short-term fluctuations) as expected. If not, make changes, and restart the timer. Installing a single compliance will automatically set another time, as dividers hardly linger. The system can be switched on again after a few seconds after switching off, since all the capacitors in the system must be discharged. Quality dielectric capacitor C4 plays a key role in the stability of the measurement time. Therefore it is necessary to use a polyester capacitor instead of electrolytic. However, it should be remembered, that the generator is not stable quartz, and its operating frequency, and, Consequently, received activation time depends on many factors, primarily on the temperature. So do not use this device for precision timing. The current value, flowing through the connector J2, limited effectiveness of current relay, the track width and by pin connection.

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