help me build a project

i've finished my battery charger for my r/c car.but the problem is i always forgot to switch off the charger and the result is my battery got very hottt..so i need a timer to swich off the charger.i need a 5minutes to 15 minutes timer.but i dont know how to make the timer

If your batteries are NiCads, letting them go hot does them not any good at all :cry:
Instead of a timer you would be better off using a temperature sensor to turn the charger off.

NiCads stay cool while accepting charge but go warm quickly once fully charged. You find temperature switches in all the battery packs for power tools, their charger switches automatically off by the temerature sensing.

You can get neat little bimetallic temperature switches, from about 40 degrees C onwards and one of these would do nicely. Make sure is an 'off when hot' type.

Using a timer would involve a lot of guesswork in setting unless your batteries are always discharged to exactly the same level.

Klaus

R/C Charger

Pay this site a visit **broken link removed**
some useful circuits and ideas pertaining to R/C.