computer controlled latching relay

Discussion in 'The Projects Forum' started by nemo1986, Mar 4, 2009.

  1. nemo1986

    Thread Starter New Member

    Mar 4, 2009
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    Hi

    I am working on a project to design a self contained cooler for a group project and I am working on the electrical system. The cooling system works by using a ammonia vapor set up to cool the food. Now I have the heating coil I am going to use but the problem is I need a latch relay to open the circuit under two conditions 1. it will shut down after a certain amount of time or the pressure changes or if the heating coil goes above a certain temp. This setup will be monitored by a computer system that will be chosen by another member of my group. My professor recommends That I use a parallel port set up but I can't find what I want or I am missing something. It will monitor a 120VAC standard wall socket at a current of 5-10 A.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Are you needing recommendations for a latching relay, or a current monitor?
     
  3. nemo1986

    Thread Starter New Member

    Mar 4, 2009
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    latching relay. I need something that will kill the voltage when the computer detects that the ammonia has evaporated or something goes wrong with the coil.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Try a P & B S89R11DAC1-12 (actually now a part of Tyco). It's 12 volt DC impulse latching DPDT, 15 amp contacts. Digi-Key has them as part #PB513 @ $45.38.
     
  5. nemo1986

    Thread Starter New Member

    Mar 4, 2009
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    And this can be controlled by a separate computer and can be open and closed by the same computer?
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    Anything that can apply 12 VDC to the coil can control it. You wil need some external hardware for that, but a resistor, logic level FET plus suppressor diode, and a 12 volt supply are about the only components necessary.
     
  7. nemo1986

    Thread Starter New Member

    Mar 4, 2009
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    what size resistor we talking about? If this works out then you just helped mesolve three weeks of headaches I needed to find this, a heating coil and a 12-14.8V battery that would last around 6-7 hours and a heating coil I found the heating coil and a 14.8V battery 9Ah (133 Wh, 7A rate) that should workout fine. Hey do you control the discharge by wire guage or do I need something else for that. Cause I will be honest batteries were never my strong suit.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    Here's a schematic of the hookup. Any logic HIGH pulse lasting a couple of 10's of milliseconds will operate the relay. It will change and hold state with each pulse
     
  9. nemo1986

    Thread Starter New Member

    Mar 4, 2009
    8
    0
    Thanks for the help this could be the answer to my problems.
     
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