Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Relay to control appliances connected to pc

  1. Mar 24, 2009 #1
    when my pc shuts off, i want to shut off a bunch of other things too-speakers, light, monitor.

    to do this i need a relay but am a little perplexed on the correct wiring.
    (Please ignore the periods. they are necessary to make this drawing look right but have no meaning)

    Voltage_____|
    . . . . . . . . . .|
    1___| . . . . . |
    . . . .| . . . . . |
    . . .coil = ). . |(
    . . . .| . . A. . .B
    2___| . . .|
    . . . . . . . |
    . . . . . . .R1 (lights, speakers)
    . . . . . . . |
    Neutral__|

    When the coil is energized(current from 1 to 2), the switch moves from B to A.

    Is it workable to also connect Voltage to 1, then to connect 2 to the hot leg of the pc power cord and then the neutral leg of the pc power cord to neutral? It would look like this:

    Voltage_____|
    | . . . . . . . . .|
    1___| . . . . . |
    . . . .| . . . . . |
    . . .coil = ). . |(
    . . . .| . . A. . .B
    2___| . . .|
    |. . . . . . .|
    PC. . . . . R1 (lights, speakers)
    | . . . . . . .|
    Neutral___|

    The idea is to get current to flow through the coil when the pc is on. This allows current to flow through R1. And when the pc is off, there is current through R1.

    The resistance through the coil is 2 kOhms and this is an A/C relay rated at 10 amps for 120 volts. or is this stupid because insufficient current will flow to the pc because the coil resistance is so high?
     
  2. jcsd
  3. Mar 24, 2009 #2

    Danger

    User Avatar
    Gold Member

    Wouldn't it be a lot easier to just plug everything into a power bar and flip the master switch?
    By the bye, on any of my non-portable Macs the shutdown automatically kills power to the monitor.
     
  4. Mar 24, 2009 #3

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    You can buy a USB connected power stip from from ecostrip for a ridiculous amount of money (thinkgeek used to do a cheap one)
    Or if you google usb controlled power strip there are dozens of DIY versions - you just switch the 110/230V live input line with a 5v relay.
     
  5. Mar 24, 2009 #4
    tnx.
    google found this for me:
    http://www.instructables.com/id/SC9F1YAFJKGWVP3/ [Broken]

    is there anything google cant do?
     
    Last edited by a moderator: May 4, 2017
  6. Mar 24, 2009 #5

    Danger

    User Avatar
    Gold Member

    I'm pretty sure that it can't teach a snake to tap-dance... but who can? :wink:
     
  7. Mar 24, 2009 #6

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Mel Brooks !

    spacemag5.jpg
     
  8. Mar 24, 2009 #7

    Danger

    User Avatar
    Gold Member

    Damn, but you're quick.
    Unfortunately, you are mistaken. Since that critter has legs, it is not a snake.
    Cudos for your response, though. :approve:
     
  9. Mar 24, 2009 #8
    There are power strips made that automatically turn on the rest of the outlets when current is detected in the "trigger" outlet. There is a threshold adjustment knob to set the sensitivity of the trigger outlet. They work with about everything once the adjustment is set.

    I forgot the company, but they are on the same page as the Kill-A-Watt meter on Amazon, which I can't get to right now.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Relay to control appliances connected to pc
  1. Connection Of Appliances (Replies: 13)

Loading...