Timer circuit design

Discussion in 'The Projects Forum' started by tigerapna, Dec 14, 2011.

  1. tigerapna

    Thread Starter Member

    Dec 14, 2011
    Hello, I am new to this forum so I would like to say HI .

    My current circuit consists of 3 24VDC relays that control 3 pumps. I want to add a timer safety circuit which checks to see if the pumps are on for an hour.

    If the pumps are on continiously for an hour, the timer circuit should switch off the relays until the reset button is pressed.

    I found this:
    but it energies the relay after the timer has pulsed . I wish to do the opposite and switch off the relay when the timer has pulsed and also reset the timer when the pump has switched off in normal operation.

    I don't know if that makes sense but any help would be greatly appreciated.
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    You could hook up the pump through the Normally closed contacts of the relay instead of the normally open contacts (on a DPDT Relay) with the circuit above to get what you are looking for.

    How accurate did your 1hour timing need to be? Within seconds? Within minutes?

    What temperature conditions will the circuit be exposed to?
  3. tigerapna

    Thread Starter Member

    Dec 14, 2011
    The one hour timing can be accurate within +/- 5 minutes.

    The temperature is around 30 degrees celcius.