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Switching 24vac

Discussion in 'Electronic Basics' started by alp, Jul 22, 2007.

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  1. alp

    alp Guest


    I would like to interupt a circuit several times a second. The circuit
    carries 24vac to a solenoid circuit under ground somewhere.

    What I want to do is open and close this circuit several times a second so I
    can actuate and un-actuate the solenoid, causing it to buzz.

    I need to find this solenoid and have been unable to do so. I hope the
    buzzing can help me home in on it.

    What I am thinking of is perhaps something run off a 555 to trigger some
    sort of electronic switch for the 24vac.

    Any ideas on chips for this purpose?


  2. Phil Allison

    Phil Allison Guest


    ** Why not feed the output of an audio amplifier into to 24 volt AC line ?

    Some screaming heavy metal music should provoke the solenoid into a bit of
    "grunging" noise so you can locate it with you ear to the ground.

    ........ Phil
  3. ehsjr

    ehsjr Guest

    For this application, just use a 555 to operate
    a relay at something between 3 and 20 Hertz. The
    relay can interrupt the 24 vac to the solenoid.
    You should add a snubber across the relay points,
    made from a 100 ohm resistor in series with a .1 uf
    250V capacitor. Make sure the relay contact
    rating exceeds the current that the solenoid draws.

  4. Jamie

    Jamie Guest

    they have wire tracers for that.
  5. alp

    alp Guest

    I didn't think a relay could operate at the frequency needed (to buzz a
    solenoid). That is why I asked about an electronic switch.
    However, your explanation seems solid (apart from my doubt about the max
    frequency the relay contacts can operate at).
    I will consider it. Thanks.

  6. alp

    alp Guest

    DJ Delorie wrote:

    Now this is an interesting idea.
    I wonder if I can fashion something without a PC parallel port. (555 would
    be fine).
    I'll have to look up more on alternistors and triacs I think.
    Thank you!

  7. alp

    alp Guest

    Yes they do. I do not wish to buy one.

  8. Jamie

    Jamie Guest

    How about using your friends metal detector for a
  9. amdx

    amdx Guest

    For this application, just use a 555 to operate
    Hi Alp,
    Here's a completely different technique you could try, I've used it very
    to locate and follow buried coax for my antennas. I saw this hint somewhere
    on the net.
    Take a small portable radio tuned to station, lay the radio down on a table
    and rotate
    the radio around, you will find a spot where the signal strength diminishes.
    there are two nulls in the signal, 180 degrees apart. If you don't find a
    good null try
    this outside on the ground or try a different station.
    Now with the radio rotated for the null, move it across the ground where
    you think
    the cable is, when you are above the cable it will transmit a signal and you
    will hear
    the radio signal. Follow the cable until the signal is no longer there, and
    you should
    be near the valve. This works great on antenna coax cables, you might have
    to disconnect
    the wires at the power source and add 10 or 20 ft of wire just to get a
    little more signal
    on the buried wire.
    Give it a try,
  10. I haven't used that method, but I have used an AM radio to
    follow buried wiring and pipes.

    I connect a battery to a small DC relay, with the coil in
    series with a normally closed contact, so that the relay
    buzzes the way a doorbell works. I connect one side of the
    battery to a ground rod and the coil end that connects to
    the contact to the conductor to be followed. The coil
    generates a noisy broad band pulse splatters all over the AM
    band. I tune the radio between stations at the low end of
    the band (where ground penetration is maximal, but antenna
    efficiency for the buried conductor in minimized, so only
    the near field is significant. I can follow the buried
    conductor by swinging the radio back and forth across the
    conductor, centering the peak of the buzz in the swing.

    I was able to help a friend find the route of a buried
    plastic sewage pipe this way, by flushing one end of a
    flexible wire, attached to a fishing bobber, down the
    toilet, to act as the radiating conductor.
  11. John Fields

    John Fields Guest

  12. DJ Delorie

    DJ Delorie Guest

    I mention alternistors and not triacs because alternistors are
    designed for inductive loads, and your solenoid is one. But you can
    use a regular optotriac (MOC30xx family) to trigger them.
  13. ehsjr

    ehsjr Guest

    A typical general purpose relay will transfer in roughly
    10 ms, so to go from de-energized to energized and back
    to de-energized, figure 20 ms. Then add a "fudge factor"
    of 150% (because we don't have the specs of the actual relay)
    to get 50 ms. That translates to 20 cycles per second -
    a typical relay can do at least that.

  14. Rich Grise

    Rich Grise Guest

    So, how did this turn out?

  15. neon


    Oct 21, 2006
    first of all how do you know that the wires are still connected to the relay? check resistance lately??????
    second any relay can and will cycle on-off if the dc power is connected through the contacts a capacitor can change the buzzer frrequency. then run the same dc trough the relay contacts to your relay power if the wires are good the relay still alive then yes you may locate it chasing the sound. drive a spike into the earth and listen. no timer LM555 REQUIRED JUST ANOTHER DPDT RELAY. GOT THAT? SIMPLE.
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