HELP - 12 Vdc Timer circuit

Discussion in 'General Electronics Chat' started by Dashboy, Jun 6, 2010.

  1. Dashboy

    Thread Starter New Member

    Jun 6, 2010
    2
    0
    Hi,

    I am not to familiar with what elctronics do what.

    I want to install a cooling fan on my motorcycle contolled by a thermal open/close switch.
    This part I understand.

    Now what I would want is after I turn off my motorcycle, I want the fan, (If already activated by thermal switch) to run for 60 seconds then turn off.

    The sensing to arm the timer will be from 12VDC loss from the alternator when I turn off the bike.

    Once I restart my motorcycle, the timer circuit is resetted and awaiting a power loss signal once again.

    How do I do this?
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    delay-on-break relay should do the trick.

    The Normally Closed relay will engage for the set amount of time after the circuit loses power.
     
  3. Dashboy

    Thread Starter New Member

    Jun 6, 2010
    2
    0
    And will this relay reset once normal power is restored?

    Do you have or know of a specfic model of relay?
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Amperite makes [or did]make thermal time delay relays. The alternator line would connect to heater, NO contacts would close when alt comes up & would turn on fan if thermal SW was colosed.
    Another option: A P-ch FET switch is on whenever T-SW & Alt are on. When Alt. goes low, C1 discharges via R2 1mΩ pot or resistor. When below bias V at + input of high Z input comparator Q1, output goes high, shutting off FET. Timing adjusted by R2, C1 & R4. D2 keeps Q1 - input V low when T-SW is open so it does not exceed Q1 VDD.
     
  5. retched

    AAC Fanatic!

    Dec 5, 2009
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