i have a generator. i want its running time.
bassically i need a timer which run the time when generator starts and stop the time when generator stop. but the time of timer did not go to zero. it remain at that time when generator stop.

 

It sounds to me like what you need is a device called an "hour meter".
Here is a link to one type of hour meter: http://www.datcon.com/products/2hdhrmtrs.htm
Here is a link to many types in the Grainger online catalog:
http://www.grainger.com/Grainger/hour-meters/counters-and-hour-meters/electrical/ecatalog/N-cr3

Basically, the hour meter is connected to the device/motor so that it runs only when the device/motor is running. The hour meter never re-sets to zero; it only counts up. They are available in electro-mechanical and wholly electronic versions.

Since these are available from so many different vendors in a wide variety of configurations, you would be much better off to simply purchase a COTS (commercial off-the-shelf) unit instead of trying to build one yourself.