voltage operated relay

Discussion in 'Automotive Electronics' started by turbo1600, Jan 12, 2016.

  1. turbo1600

    Thread Starter New Member

    Jan 12, 2016
    3
    1
    hi, after a schematic that will turn on a relay at about 13.2 vdc and stay on , until voltage drops to about 12.8 then turn of .,

    anyone help ?
    mark k
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,511
    2,369
    For the average magnetic relay you would need to set up a comparitor circuit as the hysteresis of the average relay is way more than that.
    Max.
     
  3. #12

    Expert

    Nov 30, 2010
    16,257
    6,763
    True. The last time I looked, an automotive relay was guaranteed to pull in at 80% of the label voltage and persist below 50%.
     
  4. crutschow

    Expert

    Mar 14, 2008
    12,993
    3,227
    You could use two LM339 or LM393 comparators in a window comparator configuration to control a transistor driver that energizes the relay.
     
    Last edited: Jan 12, 2016
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Here is something I did for somebody about a year ago:

    Cutin.gif
     
    cork_ie and crutschow like this.
  6. #12

    Expert

    Nov 30, 2010
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    That's why I save most of my drawings. The same questions come up, year after year.
     
  7. crutschow

    Expert

    Mar 14, 2008
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    3,227
    I like your circuit Mike.
    It's a simple voltage comparator and has a stable-trip point basically independent of the supply voltage.
    I think it meets Albert E's criteria. :)
     
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