Countdown timer switch

Discussion in 'The Projects Forum' started by jimwells41, Jan 7, 2009.

  1. jimwells41

    Thread Starter New Member

    Jan 7, 2009
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    I need a countdown timer that will switch 110v 1a.
    The timer range should be up to 12 hours.
    This is to be used to feed the charger for the battery of my electric bicycle. They say I should not let the charger operate for more than 12 hours.
    So ... i would come home, connect the charger to the battery, set the timer and forget it, as opposed to worrying about disconnecting the charger.
    I see wall mounted devices that will do the job, but $70 seems excessive. Any suggestions about dealing with this would be appreciated.

    Jim
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    Use a 4047 timer IC and a relay to control your charger.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    I have a cheapo timer I picked up a Wal-Mart for about $5. You can set on or off periods for up to 23 3/4 hours in 15 minute increments. That should be enough to turn off a charger.
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    How do you make a 12 hour timer out of a CD4047 monostable/astable multivibrator and a relay?

    Ken
     
  5. mik3

    Senior Member

    Feb 4, 2008
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    You set it as a monostable and determine the resistor-capacitor value to make a delay of 12 hours. Use a relay on its output to drive your load. Read the datasheet for how you connect it.
     
  6. eblc1388

    Senior Member

    Nov 28, 2008
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    This is interesting. Let me try to calculate the values needed.

    12 Hours is 12x60x60 seconds = 43200 seconds.

    CD4047 datasheet gives typical monostable timing to be 2.48*R*C, with limit on R to be 1MΩ max., and C to be non-polar for good timing repeatability.

    One only requires a non-polar cap of 17,420uF and bingo, a 12-hr timer.
     
  7. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Thanks for the calculation L.Chung. I thought it would be in that range.
    I think the CD4060 and a 4011 would allow more reasonable component values. ;)

    Ken

    Change: To hold the relay ON for 12 hours and then go Off, move R5 from pin3-U2 to pin4-U2. And use the Com/NC contacts on the relay.
     
    Last edited: Jan 8, 2009
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