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Electronics Forum / Basics / July 2007Switching 24vac
Hello. 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? Thanks, Alp "alp" > I would like to interupt a circuit several times a second. The circuit > carries 24vac to a solenoid circuit under ground somewhere. [quoted text clipped - 5 lines] > I need to find this solenoid and have been unable to do so. I hope the > buzzing can help me home in on it. ** 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 > What I am thinking of is perhaps something run off a 555 to trigger some > sort of electronic switch for the 24vac. A PC parallel port, an optotriac, and an alternistor should be enough for such a temporary circuit. I use 24vac switching in my furnace controller boards: http://www.delorie.com/house/furnace/ > A PC parallel port, an optotriac, and an alternistor should be enough > for such a temporary circuit. > > I use 24vac switching in my furnace controller boards: > http://www.delorie.com/house/furnace/ 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! Alp > I'll have to look up more on alternistors and triacs I think. 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. > Hello. > [quoted text clipped - 15 lines] > > Alp 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. Ed 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. Alp > For this application, just use a 555 to operate > a relay at something between 3 and 20 Hertz. The [quoted text clipped - 5 lines] > > Ed >> For this application, just use a 555 to operate >> a relay at something between 3 and 20 Hertz. The [quoted text clipped - 5 lines] >> >> Ed Hi Alp, Here's a completely different technique you could try, I've used it very successfully 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. Actually 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, Mike >>> For this application, just use a 555 to operate >>> a relay at something between 3 and 20 Hertz. The [quoted text clipped - 31 lines] > Give it a try, > Mike 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. >>>> For this application, just use a 555 to operate >>>> a relay at something between 3 and 20 Hertz. The [quoted text clipped - 52 lines] >flexible wire, attached to a fishing bobber, down the >toilet, to act as the radiating conductor. --- Slick! :-)  SignatureJF > 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. [quoted text clipped - 3 lines] > > Alp 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. Ed >>For this application, just use a 555 to operate >>a relay at something between 3 and 20 Hertz. The [quoted text clipped - 5 lines] >> >>Ed > Hello. > [quoted text clipped - 15 lines] > > Alp they have wire tracers for that. Signature"I'm never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5 > they have wire tracers for that. Yes they do. I do not wish to buy one. Alp >>they have wire tracers for that. > > Yes they do. I do not wish to buy one. > > Alp hmm. How about using your friends metal detector for a day? Signature"I'm never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5 > 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. So, how did this turn out? Thanks, Rich |
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