Here is a very useful and reliable circuit of a long duration adjustable timer using 555 IC or we can also say it long duration time delay relay. The circuit can give a time delay of 2 minutes to several hours. The time duration can be adjusted with the 1M variable resistor.
A 12V relay is derived at the output of the circuit due to which you can control any AC or DC device with the circuit.
This simple timer can be used for variety of purposes for example charging batteries and automatically disconnect them on preset time, controlling home appliance etc.
This circuit is built around the famous 555 timer IC. When the push switch S1 is pressed the circuit will activate the 12V relay and an LED for a preset time and therefore any appliance connected with the relay will be activated. Increasing the value of the capacitor Cx can further increase the time duration of the circuit for example a 3300uF capacitor can increase the duration to 2 to 3 days.