The capacitor resistor values can be worked out from the relay coil current and transistor gain.
Power off time delay relay circuit.
Timer relay drok time delay relay dc 5v 12v 24v delay controller board delay off cycle timer 0 01s 9999mins trigger delay switching relay module with lcd display support micro usb 5v power supply 4 6 out of 5 stars 132.
The circuit is based on the rc time delay and zener controlled switch.
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.
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.
The working is very simple and is explained below.
The time delay for the common emitter will be approximately 3 time constants or 3 r c.
Time delay relay can provide a short delay after power is turned on and before switching on the device.
The following circuit was requested by fastshack3.