Timed relay..kinda of

Discussion in 'The Projects Forum' started by Graphite SRT, Sep 2, 2008.

  1. Graphite SRT

    Thread Starter Member

    Jan 11, 2008
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    0
    OK, I want to have a relay activated to turn on my fans in my car for 5-10 mins after i switch off the ignition but the relay need to be turned back off and the countdown stopped/reset when the ignition is turned back on. Sounds simple but i cannot find something already made do this exactly.

    Any help on building a circuit would be helpful

    thanks
     
  2. Externet

    AAC Fanatic!

    Nov 29, 2005
    759
    57
    Cars have that type of switch for the rear defroster. No matter if you forget to turn it off, it will time out and the next time you activate will start counting again.
    The time is adjustable on a potentiometer. Canibalize one from the wreck yard and you are done.
    Miguel
     
  3. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    What are the fans for and do you know whether the ground or +12V is switched?

    Do the fans normally only work when the ignition is on?
     
  4. Graphite SRT

    Thread Starter Member

    Jan 11, 2008
    23
    0
    the fans are for engine/radiator cooling. All i need to do is ground out a relay for 5-10min when the ignition it turned off.

    The fans will work if i ground the right two relays when the ignition is turn off

    If i were to use a defroster switch how would it be automatically activated when the ignition is turned off. could i use a relay to make the contact the button normally does, but that would be like the button just being held down and it may not time out.
     
    Last edited: Sep 2, 2008
  5. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    You should be able to do this with a 555 timer:D. Essentially, 2 pulses are required: a Trigger pulse to start the timer when the ignition is turned off and a Reset pulse to reset the timer when the ignition is turned on.

    I have an idea of how this can be done but it's a bit late now so I'll take a look at it tomorrow.
     
  6. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    368
    As a basis for a prototype, I think this should do the job:
     
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