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What type of relay (or something else) for a 19" monitor???

Discussion in 'Electronic Design' started by SA Dev, Jan 8, 2004.

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  1. The narrow blade (slot) is the hot wire.
    The wide blade (slot) is the current carrying conductor that is tied
    to ground at the power panel.
  2. Sorry, the round pin is ground, the long slot is supposed to be
    Neutral, but a lot of outlets are miswired by hacks, and incompetent

    Take a look at this page: item 5-15R is a
    standard 15 Amp 120 Volt AC outlet. You will see the long slot is marked
    "W" for the white wire, or neutral. The connector should have a silver
    colored screw for the white wire, a brass color for the line, or "hot",
    and a green screw for the safety ground.

    The page: shows the
    current NEMA approved configurations, so you might want to bookmark it
    or print it out for future reference.

    We now return you to our normally scheduled programming.

    Take a look at this little cutie! ;-)

    Michael A. Terrell
    Central Florida
  3. SA Dev

    SA Dev Guest

    Excellent--thanks for the help. What type of situation would I need to be
    concerned about a diode, just so I understand?

    Have a great day,

  4. SA Dev

    SA Dev Guest

    So, in my previous post about switching an AC device like this, the right
    way to do it is to just switch the hot wire, right? That is how a power
    strip I have does it--I checked it with my multimeter. If it would be
    better, I could get a dual pole relay and switch both the hot wire and
    common wire...


  5. SA Dev

    SA Dev Guest

    Thanks for the info and the weblinks are excellent.

    Have a great day,

  6. The inductance of the relay coil acts like a current fly wheel. It
    will produce voltage that tends to not allow the current to make big
    changes in a small time. So when you first switch voltage into the
    coil, it produces a voltage almost equal to what you are applying, to
    slow the rise of the current, delaying the pull in for a millisecond
    or 3. And when you try to release the relay by turning the applied
    voltage off, it produces a spike of voltage that tries to keep the
    current flowing (which gets added to the supply voltage you are trying
    to interrupt). So either you have to pick a switching transistor (or
    whatever is operating the coil) that has a voltage capability a lot
    higher than the coil supply, and let it just suck up the coil's stored
    energy as heat (having a high voltage across the switch while the coil
    current has not yet been quenched), or you put a diode across the coil
    that gets turned on by the coil voltage reversing and let that energy
    dissipate in the resistance of the coil, itself, with a slower
    release. If you need really fast release, you put a zener diode in
    series with the coil diode, to let the reverse coil voltage get
    larger, but still limited, and pick a switching device that can handle
    that defined extra voltage.
  7. I would just switch the hot wire, if I were building your circuit. I
    might also check my outlet with an AC volt meter to make sure the wide
    blade has little voltage on it, compared to the ground pin (to make
    sure that the hot is where it is supposed to be, on the narrow blade).
  8. SA Dev

    SA Dev Guest

    Thank you! That makes sense, if I ever build something that uses a relay
    and a switching device I'll know about this gotcha!

  9. scada

    scada Guest

    Yes John, thats' true. However the first time he has a bad connection to his
    relay circuit, or decides to add a switch in series, poof! For the 50 cent
    diode, I believe it to be cheap insurance.
  10. First I try to answer the question asked.

    After that I might give free advice. ;-)
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