The capacitor resistor values can be worked out from the relay coil current and transistor gain.
Power off time delay relay circuit.
The working is very simple and is explained below.
The following circuit was requested by fastshack3.
This would be done in 12v and the sequence will be initiated by a manual switch.
Very handy and simple circuit if your looking to have lights accessories or other devices power off after a preset time has elapsed after power is no longe.
Delay timer with relay i am looking to build a circuit that would control an output relay.
For example a 120 ohm relay coil will draw 100 ma at 12 volts and assumming a transistor gain of 30 the base current will be 100 30 3 ma.
The time delay for the common emitter will be approximately 3 time constants or 3 r c.
The circuit is based on the rc time delay and zener controlled switch.