Delay Timer Relay Circuit

Introduction:

                Welcome to the "Time Delay Relay Controller Circuit" project utilizing the BC 547 Transistor. This transistor functions as a relay driver, controlling the relay and enabling the operation of connected appliances within a specified time duration, such as 10 seconds. This circuit is a versatile solution for operating various timer-controlled appliances. Let's explore the construction of this circuit in the following guide.

Connection:

                             Begin by fitting and soldering the BC 547 Transistor onto the DOT Board. Attach the 10K Resistor to the base of the transistor and connect the +ve of the 1000μF/16V Capacitor to the other pin of the 10K Resistor. Introduce a micro push switch between the +ve and base of the transistor. Connect the -ve of the capacitor and the emitter of the transistor to the power supply's -ve. Proceed to connect the 1st coil pin of the relay to the collector pin of the transistor and connect the relay's 2nd pin to the +ve of the power supply. Insert a 1N4007 Diode between the relay's pins, with the anode pin of the diode to the 2nd +ve pin of the relay and the cathode pin to the 1st pin of the transistor's collector. Complete the circuit by connecting the +ve pin of the power supply to the relay's 2nd pin and the -ve pin of the power supply to the -ve of the 1000μF Capacitor.

Note:

         For adjusting the time duration, modify the values of C1 (capacitor) and R1 (resistor).

Circuit Diagram:

Part List:

1)BC 547 Transistor =1 (Any NPN Transistor)

2)1000μF/16V Capacitor =1

3)10KΩ ¼ W Resistor =1

4)Micro Push Switch =1

5)1N4007 Diode =1

6)9V Power Supply =1

7)6V SPDT Relay =1

8)DOT Board =1

9)Some Wires

10) Some Connectors

Working:

           This circuit operates based on the principle of the capacitor charging and discharging method. Upon powering the circuit, the C1 capacitor charges fully. Pressing the SW1 switch allows the capacitor to discharge through the 10K resistor, reaching the base of the Q1 transistor. Consequently, the relay is switched on, activating the connected appliances. As the capacitor discharges, the relay remains on, and when the capacitor is fully discharged, the relay turns off. The working principle is expressed as follows: 

Capacitor discharge time + Resistor current flowing time = Relay's working time.

The delay time can be calculated using the formula: Time constant = Capacitance (F) × Resistance (Ω). For example, with a 100μF capacitor and 20K resistance, the time constant is 0.0001F × 20,000Ω = 2 seconds. Multiply the time constant by a factor (e.g., 5) to determine the capacitor charge time, such as 10 seconds.

Example Project Records:

• 1000µF Capacitor and 10KΩ = 45 Seconds
• 1000µF Capacitor and 22KΩ = 1 Minute 10 Seconds
• 2200µF Capacitor and 10KΩ = 1 Minute 38 Seconds
• 2200µF Capacitor and 22KΩ = 2 Minute 42 Seconds

Importance of Delay Timers:

    In various electronic circuit applications, a delay of seconds or minutes is crucial for ensuring correct operation. Without the specified delay, circuits could malfunction or get damaged.

Uses of this Circuit:

        This circuit can be employed as a stabilizer, preventing voltage spikes from damaging AC appliances. By utilizing this circuit, you can safeguard your appliances from potential harm caused by voltage fluctuations.

 

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                                                       By,

G. Guruvel Sarveshwar,

EEE Dept.