Instant on, delay off

Discussion in 'General Electronics Chat' started by electricnewb, Nov 9, 2013.

  1. electricnewb

    Thread Starter New Member

    Nov 9, 2013
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    I have what I think is a basic timer need however I cannot find a circuit. Let me describe the project so I can see if I am even thinking in the right direction. I have a 12v solar setup in my barn. For some reason my son/wife have an issue remembering to turn the lights off and keep killing my batteries. What I think I need is a circuit (555 based?) that I can use a toggle switch with (turn the 12v on to the circuit) at which point the timer will start without the need of the push of another button and it will pull in a NO relay to the closed position turning on the lights. If I toggle the switch off removing the 12v it will obviously remove the power to the circuit/relay and the lights go off OR if someone forgets to turn the switch off the timer will handle opening the relay at the end of the time. I would like the time to be adjustable from somewhere around 10 minutes to 1hr plus. I was thinking of using an automotive relay because they are heavy duty and built for 12vdc loads. Any help would be much appreciated.
     
  2. #12

    Expert

    Nov 30, 2010
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    You can't get an hour out of a 555. You could add a Johnson counter (CD4060?) or you could buy a wind up timer switch and forget the electronics. Believe me, I've done it.
     
  3. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    You can delay hours with a 555 timer. A C value of 330uF and an R value of 10 meg will give you just over an hour (3630 seconds) before shutting off. Set it up with a relay and you're set.

    [​IMG]

    Just remember that the Trigger pin must be connected to ground (ideally through a pushbutton switch with a pull-up resistor) to trigger the output.
     
    Last edited: Nov 10, 2013
  4. #12

    Expert

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    I hope you're speaking from experience. The specs for aluminum electrolytics do not support such claims, but I know from personal experience that you can get more than you expected...I just don't remember if you can get to an hour.
     
  5. DerStrom8

    Well-Known Member

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    You do have a point, this was purely based on calculation. However, I have built long-delay 555 circuits similar to this one and didn't have a problem. It couldn't hurt to give it a try, at least.
     
  6. ScottWang

    Moderator

    Aug 23, 2012
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    I thought about that, but he needs the pot to replace the fixed resistor, so maybe he needs that 1MΩ pot and cap changing to 3300uf, and should be using cmos type as ICM7555.

    I didn't try it to take the time so long, but I saw someone to set it to about 30 minutes.
     
  7. DerStrom8

    Well-Known Member

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    Why would he need to replace the fixed resistor with a pot? And sure, CMOS would use less juice but that wasn't the point of the discussion, I just wanted to give him the general schematic he'd need to achieve his goal.
     
  8. #12

    Expert

    Nov 30, 2010
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    I think that covers the adjustable part.
     
  9. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Woops, I have been missing a lot of things lately. Sorry about that :rolleyes:

    In that case, you can find 10M pots. You can always tie it in series with a lower value pot to have a coarse and fine time duration adjustment.
     
    #12 likes this.
  10. ScottWang

    Moderator

    Aug 23, 2012
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    I think if using rotary switch, 2 poles - 6 positions to switched the resistors is another choice.
     
  11. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Personally I'd go the CD4060 route (as per #12). No need then for high value electrolytics with their associated unpredictable leakage (hence dodgy timing).
     
  12. DerStrom8

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    You guys are probably right. The CD4060 is the way to go, and it's cheap and easy to set up.
     
  13. #12

    Expert

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    Experience trumps book learnin'.:D
     
  14. electricnewb

    Thread Starter New Member

    Nov 9, 2013
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    I was originally looking at a wind up timer but I could only find AC rated devices and I have read using AC rated switches on DC is not a good idea. I wouldn't mind still going this way as a quick resolution but still messing around with a circuit for future needs.

    Thanks all for your replies. Great info.
     
  15. #12

    Expert

    Nov 30, 2010
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    If that's what you need, that's what you should ask about.
    Ve haf vays of dealing mit deese tings.
     
  16. electricnewb

    Thread Starter New Member

    Nov 9, 2013
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    If making an AC wind up switch work with DC is the answer to what I need to do then great. I am sure there are plenty of ways to go about what I am looking to do which is why I tried to describe as accurately as I could what that was. The easier the better for the electrical challenged like me :)
     
  17. #12

    Expert

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    Everybody focused on the timing because you did not say the wind up timer only claimed to work on AC. Start a thread with the specifications on the switch, the DC voltage, and the maximum current you will be using. You might need a snubber circuit to break the DC arc when the switch opens.

    "Using AC rated contacts for a DC circuit"
    as compared to, "Time on, Time off"
     
  18. electricnewb

    Thread Starter New Member

    Nov 9, 2013
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    I was not even thinking wind up switch any more at the point in which I posted. I was so far past that because I didn't think it was a viable solution. Thanks for the suggestion. I will create a new posting.
     
  19. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    What current do you need to switch?
     
  20. doug08

    Member

    Jan 30, 2011
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    You can do that with this circuit here. Once power is applied to the circuit, the load comes on for a set duration then turns back off, even though power is still applied to the 555 circuit. If they leave the light on, then when you return to the barn, you simply flip the switch down then up to reset the circuit. Output will be relay contacts. You can adjust the duration by raising the cap value from pin 2 to ground. Go high as possible for more minutes, or increase the resistor values.

    Circuit here:
    https://www.youtube.com/watch?v=q1Gj_mkMcI0
     
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