Can anyone help me to make a simple adjustable timer that can be used to switch a 9-12 Volt relay. I need the relay to turn on when a push button is engaged/pressed, and automatically turn off when the timer reaches the set value. I need the timer to turn off the relay after 0 minutes, to a max of 4 hours. There is no need for any sort of display, although a simple one wold be very helpful.

Thank You For Reading And Posting Any Posts!!!!!!!!!

 

How accurate does the 4 hour thing have to be?
The link here and the attached schematic shows a popular/typical method for what you are looking for.
Increasing the C2 100uf cap with a larger one (4700uf+) will give you a pretty reliable, fairly accurate extended time timer circuit.
delays of many hours is possible.

Is is no harder than this:
http://www.apogeekits.com/start_stop_timer_k2579.htm

$12 US dollars
can the parts be bought that cheap?

If accuracy is needed, a different avenue may be pursued.

EDIT: the words "fairly accurate" were added.
EDIT: 4700uf+ was added

 

Another option for a long term timer: http://www.zen22142.zen.co.uk/Circuits/Timing/24hour.htm

Ken

 

OP,
depending on your experience level, I would opt for the circuits Ken posted for better performance and accuracy.

The circuit I posted works very well and accurate up to about 4 to 5 hours but after that it is a bit iffy. It could be off a couple minutes either way after 4 - 4.5 hours.
That is with a 4700uf capacitor at C2 when looking for long time delays

a suggestion would be to use switches at C2 to select different values of capacitance for C2 for more sensitive adjustments at lower delay time needs.

like a 100uf for 0 to 15 minute range
1000uf for 15 to 60 minute range
2200uf for 1 to 2 hour range
4700 for 2 to 4 hour range.

readings for the graph were with 9 volts supply voltage