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| Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Delay on a mains-powered relay?
"DaveC" wrote in message
al.net... I've got several remote alarm sensors triggered by 120vac relays. When power fails, the alarm calls the right folks. Problem is that even the small power glitches get these guys out of bed. Not a good thing. How can I delay the de-energizing of these relays? 5 minutes without power is OK. Will a series diode and shunt cap do the trick? If so, what size cap? If not, what're my options? The relay is similar to this one: http://tinyurl.com/6pppw Thanks, -- Please, no "Go Google this" replies. I wouldn't ask a question here if I hadn't done that already. DaveC Hi. Hmm, sorry but you should Goo.... Altavista this. Use the term 'delay relay'. Here's one: http://www.automatictiming.com/pages...layrelays.html The more run-of-the-mill parts places don't sell them, but relay specialists do (not sure what the situation is in your area). Farnell also have these (they're possibly easier to use): http://au.farnell.com/jsp/endecaSear...erDisplay=true (They operate USA too, I just didn't have the link handy) Cheers. Ken |
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What would be the purpose of setting off ur alarm every time power
fails?? Not being nosey, it's just that the only alarm panels (fire/security) I've seen had some form of battery backup, whether it be Nicad, Lead Acid, etc. to keep the system running normally under power failure. |
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Not being nosey, it's just that the only alarm panels
(fire/security) I've seen had some form of battery backup, whether it be Nicad, Lead Acid, etc. to keep the system Yes, but they still dial home to report AC loss. |
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k, then yeah the brit guy above pointing toward the time delay relays
might be a way to go... |
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On Tue, 4 Jan 2005 18:09:21 -0800, DaveC wrote:
I've got several remote alarm sensors triggered by 120vac relays. When power fails, the alarm calls the right folks. Problem is that even the small power glitches get these guys out of bed. Not a good thing. How can I delay the de-energizing of these relays? 5 minutes without power is OK. Will a series diode and shunt cap do the trick? If so, what size cap? If not, what're my options? The relay is similar to this one: http://tinyurl.com/6pppw Assuming power is available to make the call, your control circuit obviously doesn't depend on 120VAC being present, to function. It is also unlikely that your remote sensors run on 120VAC, as this could represent an unneccessary safety hazard. Therefore the delay is best performed in the device's control section, using the power provided to perform the control function. 5 minutes is an incredibly long delay to ask of a de-energized relay. It also could represent a signifigant security breach, if ignored. Why power loss should affect remote sensors is a question you should raise with the vendor. You should get the liable vendor or service rep to set the product up to meet realistic expectations that don't compromise security or convenient function. ............................................... Imagine if the delay was required of the hardware relay alone - assuming a 100mW coil , that drops out at 45% of the label voltage; 5 minutes hold-up requires 30j minimum of stored energy. (.1 x 60 x 5) If the initial stored voltage was 165V, and drop-out was 75V, the storage cap required would be 700uF If the initial stored voltage was 12v and dropout was 5V4, the storage cap required would be 3 Farads. .................................................. .. This example used an extremely sensitive device - your referenced part consumes 80 times the power in the example and would require 80 times the stored energy, 80 times the capacitance. The obvious source of stored energy for any controlled delay is the controller's supply. RL |
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"DaveC" wrote in message al.net... | I've got several remote alarm sensors triggered by 120vac relays. When power | fails, the alarm calls the right folks. | | Problem is that even the small power glitches get these guys out of bed. Not | a good thing. | | How can I delay the de-energizing of these relays? 5 minutes without power is | OK. Will a series diode and shunt cap do the trick? If so, what size cap? If | not, what're my options? The normal method is a relay with a hydraulic delay. This means you don't need a no fail power supply. However these days, if you have backup power, there are solid state equivalents. For your method you would need a large cap run off say, 12 VDC - maybe 1000 uF and up. N |
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"DaveC" wrote in message al.net... So the answer is... no. If power fails at the remote site, so does the control circuitry and its power. So a traditional delay relay won't work. The relay, powered by mains, simply opens the wireless sensor's sense circuit when power goes away. I just want it to do so after waiting a few minutes to see if power comes back on. The alarm isn't for security purposes, just for letting those responsible know that certain things have occurred, one of which is power fail. The sensor is a wireless device run on a lithium battery, and is a packaged deal so has no spare power available. The relay's not near the alarm CPU, so that power isn't available, either. Suggestions for a simple mains-powered circuit that will open a pair of contacts about 5 minutes after de-energizing? If it's to be battery-powered, it needs to be super-low drain. I rather keep battery replacements down to every 2 years, at most. An idea that just struck me: the presence of mains power could keep this circuit de-energized. When power fails, the battery is connected to the circuit which starts the countdown. When zero is reached (ie, 5 minutes have passed), a pair of contacts would open. And the energizing circuit (triggering these contacts) would only have to be a one-shot; once the alarm is triggered, the circuit could de-energize. That way the battery is utilized only briefly, during power-fail situations. How might I construct such a circuit? Thanks, -- Please, no "Go Google this" replies. I wouldn't ask a question here if I hadn't done that already. DaveC This is an invalid return address Please reply in the news group I never cease to be amazed at the questions asked in this NG from people who do not have a clue from grade school experiments about electronics but want to design or modify industrial situations where some manager should be putting up the money to employ a competent engineer skilled in the particular area. Relying on poorly informed advice is asking for trouble and a sure course to the courts for a damages claim. -- John G Wot's Your Real Problem? |
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I read in sci.electronics.design that DaveC wrote (in
et) about 'Delay on a mains-powered relay?', on Tue, 4 Jan 2005: I've got several remote alarm sensors triggered by 120vac relays. When power fails, the alarm calls the right folks. Problem is that even the small power glitches get these guys out of bed. Not a good thing. How can I delay the de-energizing of these relays? 5 minutes without power is OK. Will a series diode and shunt cap do the trick? If so, what size cap? Impractically big. If you get one big enough, Feerguy will want to hear from you. (;-) If not, what're my options? Back-up battery and inverter. A standard UPS would probably do. Do you know how much power the system consumes? -- Regards, John Woodgate, OOO - Own Opinions Only. The good news is that nothing is compulsory. The bad news is that everything is prohibited. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk |
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In alt.engineering.electrical DaveC wrote:
The relay, powered by mains, simply opens the wireless sensor's sense circuit when power goes away. I just want it to do so after waiting a few minutes to see if power comes back on. Can you use a solid state relay or a DIP relay, instead of the presumably larger relay you're using now? If so, the coil current will be much less, and you might be able to get away with something like a wall transformer, a big capacitor, and the relay. The time delay won't be very exact, but it may work for your application. Matt Roberds |
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"DaveC" wrote in message al.net... How can I delay the de-energizing of these relays? Use a Thermal Relay - maybe called "Delay Relay". Best approach is to find out what the format/socket is, then one of the suppliers of process control gear will have something that plug into it. |
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#11
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In article et,
DaveC wrote: How can I delay the de-energizing of these relays? 5 minutes without power is OK. Use something like this maybe. View in fixed width font. ____ +---------+ +------|AC +DC|---+-----+ +----Out | | | | | _|_ | )||( | Bridge | +|C | | o | 120Vac )||(18Vac |Rectifier| === | RL|----|N/O )||( | | | |_ _| o | | | | | | | | +---------+ +------|AC____-DC|---+-----+ +----Out A 120:18V transformer on the mains, bridge rectifier, capacitor smoothing, and 24V comms relay. Relays have an On/Off hysteresis. Once it has been energised, a 24V comms relay will not then release until the voltage has reduced to below about 8V. 24V sinking to 8V is not far off T = R*C. A standard 24Vdc high sensitivity comms relay has a coil resistance of about 2900 ohms. If C= 47000uF then the the relay will be held closed for about 136 secs after a mains failure. A 47000uF (at 35vdc working) is not cheap, and the thing is a little clunky, but easy to put together and not much to go wrong. -- Tony Williams. |
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DaveC wrote:
I've got several remote alarm sensors triggered by 120vac relays. When power fails, the alarm calls the right folks. Problem is that even the small power glitches get these guys out of bed. Not a good thing. How can I delay the de-energizing of these relays? 5 minutes without power is OK. Will a series diode and shunt cap do the trick? If so, what size cap? If not, what're my options? The relay is similar to this one: http://tinyurl.com/6pppw Thanks, Someone suggested hydraulic. I was thinking pneumatic. Checkout: http://ecatalog.squared.com/catalog/.../17321027.html Not cheap but do have a 5 min +/- 12% version. |
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I don't know what is powering the relays, but can you use a UPS to keep it
powered, but then time out? WT "No Spam" wrote in message ... DaveC wrote: I've got several remote alarm sensors triggered by 120vac relays. When power fails, the alarm calls the right folks. Problem is that even the small power glitches get these guys out of bed. Not a good thing. How can I delay the de-energizing of these relays? 5 minutes without power is OK. Will a series diode and shunt cap do the trick? If so, what size cap? If not, what're my options? The relay is similar to this one: http://tinyurl.com/6pppw Thanks, Someone suggested hydraulic. I was thinking pneumatic. Checkout: http://ecatalog.squared.com/catalog/.../17321027.html Not cheap but do have a 5 min +/- 12% version. |
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No.These relays are designed to work in ac.There's no way in storing ac in a
capacitor and diode circuit.Only expensive inverter designs.You need some engineer to construct a dedicated circuit, maybe with battery, for your purposes. -- Tzortzakakis Dimitri?s major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr ? "DaveC" ?????? ??? ?????? al.net... I've got several remote alarm sensors triggered by 120vac relays. When power fails, the alarm calls the right folks. Problem is that even the small power glitches get these guys out of bed. Not a good thing. How can I delay the de-energizing of these relays? 5 minutes without power is OK. Will a series diode and shunt cap do the trick? If so, what size cap? If not, what're my options? The relay is similar to this one: http://tinyurl.com/6pppw Thanks, -- Please, no "Go Google this" replies. I wouldn't ask a question here if I hadn't done that already. DaveC This is an invalid return address Please reply in the news group |
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John G wrote:
"DaveC" wrote in message al.net... So the answer is... no. If power fails at the remote site, so does the control circuitry and its power. So a traditional delay relay won't work. The relay, powered by mains, simply opens the wireless sensor's sense circuit when power goes away. I just want it to do so after waiting a few minutes to see if power comes back on. The alarm isn't for security purposes, just for letting those responsible know that certain things have occurred, one of which is power fail. The sensor is a wireless device run on a lithium battery, and is a packaged deal so has no spare power available. The relay's not near the alarm CPU, so that power isn't available, either. Suggestions for a simple mains-powered circuit that will open a pair of contacts about 5 minutes after de-energizing? If it's to be battery-powered, it needs to be super-low drain. I rather keep battery replacements down to every 2 years, at most. An idea that just struck me: the presence of mains power could keep this circuit de-energized. When power fails, the battery is connected to the circuit which starts the countdown. When zero is reached (ie, 5 minutes have passed), a pair of contacts would open. And the energizing circuit (triggering these contacts) would only have to be a one-shot; once the alarm is triggered, the circuit could de-energize. That way the battery is utilized only briefly, during power-fail situations. How might I construct such a circuit? Thanks, -- Please, no "Go Google this" replies. I wouldn't ask a question here if I hadn't done that already. DaveC This is an invalid return address Please reply in the news group I never cease to be amazed at the questions asked in this NG from people who do not have a clue from grade school experiments about electronics but want to design or modify industrial situations where some manager should be putting up the money to employ a competent engineer skilled in the particular area. Relying on poorly informed advice is asking for trouble and a sure course to the courts for a damages claim. Engineering in the U.S. has never had the political clout needed for effective enforcement of registration laws. A PE license carries with it almost no recognition in a world where just about anyone can get away with calling themselves an engineer (except where public funds are involved). Doctors and lawyers, and even beauticians, have done a better job getting their expertise recognized IMHO. -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#17
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Cheap microcontroller circuit, grounded to the low side of the wireless
sensor's sense contacts. Use the existing relay to signal the uC, and a mosfet to open the connection. Depending on how much power the wireless is providing to monitor the sense you may even be able to power just off that, but if not, decently careful design on a ultra-low power microcontroller should allow you to run for practically the shelf life of the battery. DaveC wrote: So the answer is... no. If power fails at the remote site, so does the control circuitry and its power. So a traditional delay relay won't work. The relay, powered by mains, simply opens the wireless sensor's sense circuit when power goes away. I just want it to do so after waiting a few minutes to see if power comes back on. The alarm isn't for security purposes, just for letting those responsible know that certain things have occurred, one of which is power fail. The sensor is a wireless device run on a lithium battery, and is a packaged deal so has no spare power available. The relay's not near the alarm CPU, so that power isn't available, either. Suggestions for a simple mains-powered circuit that will open a pair of contacts about 5 minutes after de-energizing? If it's to be battery-powered, it needs to be super-low drain. I rather keep battery replacements down to every 2 years, at most. An idea that just struck me: the presence of mains power could keep this circuit de-energized. When power fails, the battery is connected to the circuit which starts the countdown. When zero is reached (ie, 5 minutes have passed), a pair of contacts would open. And the energizing circuit (triggering these contacts) would only have to be a one-shot; once the alarm is triggered, the circuit could de-energize. That way the battery is utilized only briefly, during power-fail situations. How might I construct such a circuit? Thanks, |
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If you're in the US, try http://www.Grainger.com and do a key word
search using 120V off delay relay. You should be able to find something that would work. DaveC wrote: I've got several remote alarm sensors triggered by 120vac relays. When power fails, the alarm calls the right folks. Problem is that even the small power glitches get these guys out of bed. Not a good thing. How can I delay the de-energizing of these relays? 5 minutes without power is OK. Will a series diode and shunt cap do the trick? If so, what size cap? If not, what're my options? The relay is similar to this one: http://tinyurl.com/6pppw Thanks, |
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"DaveC" wrote in message al.net... | So the answer is... no. | | If power fails at the remote site, so does the control circuitry and its | power. So a traditional delay relay won't work. Look for a spring powered timer then. They use an AC clock motor to hold them at, say, 5 minutes. When the power goes off the spring unwinds until the clock goes to zero and the contacts close/open. When the power is restored the motor rewinds the timer to 5 minutes. Looks a bit like a cheap cooking timer on a frame. http://www.thomasregisterdirectory.c...0014366_1.html N |
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"CJT" wrote in message ... | It's an AC relay. Just how do you intend to attach that "big capacitor?" Obviously use a light (0.5W) DC relay! http://www.nteinc.com/relay_web/R16.html N |
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DaveC wrote:
So the answer is... no. If power fails at the remote site, so does the control circuitry and its power. So a traditional delay relay won't work. The relay, powered by mains, simply opens the wireless sensor's sense circuit when power goes away. I just want it to do so after waiting a few minutes to see if power comes back on. The alarm isn't for security purposes, just for letting those responsible know that certain things have occurred, one of which is power fail. The sensor is a wireless device run on a lithium battery, and is a packaged deal so has no spare power available. The relay's not near the alarm CPU, so that power isn't available, either. Suggestions for a simple mains-powered circuit that will open a pair of contacts about 5 minutes after de-energizing? If it's to be battery-powered, it needs to be super-low drain. I rather keep battery replacements down to every 2 years, at most. An idea that just struck me: the presence of mains power could keep this circuit de-energized. When power fails, the battery is connected to the circuit which starts the countdown. When zero is reached (ie, 5 minutes have passed), a pair of contacts would open. And the energizing circuit (triggering these contacts) would only have to be a one-shot; once the alarm is triggered, the circuit could de-energize. That way the battery is utilized only briefly, during power-fail situations. How might I construct such a circuit? Thanks, Refer to the post by Tony Williams. There might be a cheaper way. As he mentioned, the capacitor is expensive - you'll pay over $15.00 dollars for one. The alternative described below would cost a lot less. The super caps would cost you $1.70 for 2. The opto costs 50 cents. The voltage regulator costs another 50 cents. You can get 2 10 K pots for a dollar. Add another dollar for the 1000uf cap and resistor. I assume same price for the transformer as in the relay design. You'll save at least $10.00 per sensor, if the idea works. Since you have a number of sensors, it seems worth at least trying one as proposed below. I do not know if it is practical for you, or if it will work, since I don't have specs on the existing setup. You *may* be able to use an optoisolator, a super cap, and a potientiometer instead of the relay. The potientiometer would allow you to adjust the delay time. You would need to use a lower voltage transformer and a regulator IC. The cost would be a lot lower. The key is the current sense loop - without specs, I don't know if an optoisolator will work. Here's the details if you decide to try it. Here's Tony's circuit, modified for an optoisolator: View in fixed width font. ____ +----+ +---|AC +DC|--+--7809---+---+-------+ | | | | | | +|C2 | __|__ )||( | | +|C1 | === R1 | + |--+Sense 120 )||(12 |Rect. | === | | | |Opto | Vac )||(Vac| | | | +|C3 P-+ |__-__|--+Loop )||( | | | | === | | | | | | | | | | | | | +----+ +---|AC_-DC|--+---+-----+---+--+----+ C1 is a 1000 uf 25 volt cap. C2 and C3 are .1 farad 5 volt super caps. (Allelectronics sells these for 85 cents each) R1 is a 100 ohm 1/4 watt resistor. P is a 10K potentiometer. The opto is a 4N35. The 7809 is a 9 volt three terminal IC voltage regulator. The sense loop is connected to the existing relay points at present. I don't know which is + and which is minus, but polarity is important when you connect it to the opto. |
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On Wed, 05 Jan 2005 10:39:55 -0700, Richard Henne
wrote: http://www.Grainger.com You're right. They appear to do it all for you for $85.00. Notice the total power consumption is 180mW, so the 'relay' must be quite low power to be included in the budget. http://makeashorterlink.com/?M2F312B2A RL |
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DaveC wrote:
So the answer is... no. If power fails at the remote site, so does the control circuitry and its power. So a traditional delay relay won't work. The relay, powered by mains, simply opens the wireless sensor's sense circuit when power goes away. I just want it to do so after waiting a few minutes to see if power comes back on. The alarm isn't for security purposes, just for letting those responsible know that certain things have occurred, one of which is power fail. The sensor is a wireless device run on a lithium battery, and is a packaged deal so has no spare power available. The relay's not near the alarm CPU, so that power isn't available, either. Suggestions for a simple mains-powered circuit that will open a pair of contacts about 5 minutes after de-energizing? If it's to be battery-powered, it needs to be super-low drain. I rather keep battery replacements down to every 2 years, at most. An idea that just struck me: the presence of mains power could keep this circuit de-energized. When power fails, the battery is connected to the circuit which starts the countdown. When zero is reached (ie, 5 minutes have passed), a pair of contacts would open. And the energizing circuit (triggering these contacts) would only have to be a one-shot; once the alarm is triggered, the circuit could de-energize. That way the battery is utilized only briefly, during power-fail situations. How might I construct such a circuit? Thanks, Here's an even better mod to Tony's circuit. You need 4 parts - all available from Allelectronics: 5 volt regulated wall wart p/n DCTX-512 $3.50 Minature 4.5 volt relay p/n RLY-639 $0.75 1N4001 diode (1 needed) p/n 1N4001 15 for $1.00 1 farad 5.5 volt super cap p/n CBC-12 $3.50 D Wall + ------|---+-----+ Wart +|C | === Relay | | - -----------+-----+ I suspect the relay will stay energized longer than 5 minutes. You can add a second diode to reduce the time. You might need to add resistance in parallel with the super cap to reduce it further. This depends on the characteristics of the relay - I don't have one to test. Ed |
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On Tue, 4 Jan 2005 18:09:21 -0800, DaveC wrote:
I've got several remote alarm sensors triggered by 120vac relays. When power fails, the alarm calls the right folks. Problem is that even the small power glitches get these guys out of bed. Not a good thing. How can I delay the de-energizing of these relays? 5 minutes without power is OK. Will a series diode and shunt cap do the trick? If so, what size cap? If not, what're my options? The relay is similar to this one: http://tinyurl.com/6pppw Thanks, -- Please, no "Go Google this" replies. I wouldn't ask a question here if I hadn't done that already. DaveC This is an invalid return address Please reply in the news group It is likely that your wireless device has an input circuit with a dc voltage across the inputs when the input is open (that is how the open contacts are sensed). One side is likely common with one terminal of the battery. You should try putting a power FET device across the input (source and drain) and using a capacitor from source to gate to hold the FET on for a period after your relay opens. A resistor across the capacitor sets the discharge period. I would start with 470 MF and 1meg resistor for 4-5 minutes delay (depends on gate voltage on turn-off, device specific). If the battery negative is common to one of the input terminals, use a N-channel FET (I did something similar with an IRF520, way over kill on current, but you are not likely to damage it). If the wireless device voltage is only 3 volts, you will need a FET designed for logic level gate voltages. Connect as follows: Source of FET to - input terminal Drain of FET to the other input terminal Capacitor negative (use 16V cap) to Source Capacitor positive to Gate 1 meg resistor across capacitor 100K resistor to battery +, other side of 100K to one of your relay contacts Other relay contact to Gate. Use a grounded soldering iron as the FET gate can be damaged by static electricity. If the battery positive is common to one of the input terminals, use a P-channel FET and reverse all polarities listed above. When the relay contacts are closed, the 100K resistor uses the battery to charge the capacitor. Voltage on the capacitor keeps the FET ON. When the relay contacts open (on power fail) the capacitor holds a charge while the 1 meg resistor discharges the capacitor. At some low voltage on the Gate, the wireless sensor will detect an open circuit and send the alarm. Experiment with resistance and capacitance to get an acceptable time delay. If you shop the parts, likely cost per circuit is USD $2.00-4 .00. Bill Kaszeta Photovoltaic Resources Int'l Tempe Arizona USA |
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DaveC wrote:
I've got several remote alarm sensors triggered by 120vac relays. When power fails, the alarm calls the right folks. Problem is that even the small power glitches get these guys out of bed. Not a good thing. How can I delay the de-energizing of these relays? 5 minutes without power is OK. Will a series diode and shunt cap do the trick? If so, what size cap? If not, what're my options? The relay is similar to this one: http://tinyurl.com/6pppw Thanks, Here's what you do. Put a cheap answering machine on the same power circuit that you're trying to monitor, and connect it to the phone line that the call gets made on. Tell the guys that when they get a call (they'll still be awakened, so perhaps this is not a perfect solution) to call back to that number. If the answering machine answers, it has power, and hence so does the equipment. If the answering machine fails to answer, get in the truck. ;-) -- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form . |
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#27
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DaveC wrote:
I've got several remote alarm sensors triggered by 120vac relays. When power fails, the alarm calls the right folks. Problem is that even the small power glitches get these guys out of bed. Not a good thing. How can I delay the de-energizing of these relays? 5 minutes without power is OK. Will a series diode and shunt cap do the trick? If so, what size cap? If not, what're my options? The relay is similar to this one: http://tinyurl.com/6pppw Thanks, -- Please, no "Go Google this" replies. I wouldn't ask a question here if I hadn't done that already. Look for a TDDO (Time Delay Drop Out) relay. -- Paul Hovnanian ------------------------------------------------------------------ Reject nihilism! |
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"NSM" wrote in message news:jDJCd.44550$Y72.1684@edtnps91... "DaveC" wrote in message al.net... | I've got several remote alarm sensors triggered by 120vac relays. When power | fails, the alarm calls the right folks. | | Problem is that even the small power glitches get these guys out of bed. Not | a good thing. | | How can I delay the de-energizing of these relays? 5 minutes without power is | OK. Will a series diode and shunt cap do the trick? If so, what size cap? If | not, what're my options? The normal method is a relay with a hydraulic delay. This means you don't need a no fail power supply. However these days, if you have backup power, there are solid state equivalents. For your method you would need a large cap run off say, 12 VDC - maybe 1000 uF and up. N Just put a delay circuit in between the relay contacts and whatever (assuming low voltage) signal the control to the alarm panel. A 555 IC driving a small low voltage relay should do the trick. |
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"James Sweet" wrote in message news:fA3Dd.26413$2X6.14665@trnddc07... | But it sounds like the 120v coil is used to detect mains failure, power goes | out, relay loses power, contacts open/close, triggering the alarm. The relay | can be left alone, you only have to mess with the low voltage signal it | switches. If he wants to use a cap to delay it the lower power the better. Even a reed relay will work OK and keep the cap size down. That's the key - run from a rectifier circuit. N |
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"Ross Herbert" wrote in message ... | It seems to me that the OP would prefer to use what hardware exists | now in order to minimise expense and the complexity involved in a | complete re-design of what he now has. The relay he is using now is a | 3 pole changeover unit so depending upon what is currently connected | to the relay contacts will have some bearing on what he can do in the | easiest and most cost effective manner. .... I remember small, inexpensive delays that used an AC clock motor to wind them up. When the power went off they ran down and switched contacts. I suggested that previously. N |
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Ross Herbert wrote:
On Fri, 07 Jan 2005 12:35:17 GMT, Ross Herbert wrote: On Thu, 06 Jan 2005 16:00:50 GMT, "NSM" wrote: "Ross Herbert" wrote in message ... | It seems to me that the OP would prefer to use what hardware exists | now in order to minimise expense and the complexity involved in a | complete re-design of what he now has. The relay he is using now is a | 3 pole changeover unit so depending upon what is currently connected | to the relay contacts will have some bearing on what he can do in the | easiest and most cost effective manner. ... I remember small, inexpensive delays that used an AC clock motor to wind them up. When the power went off they ran down and switched contacts. I suggested that previously. N Granted, such a device will work but it is hardly an elegant technical solution. The whole idea of technology in industry is to make the operation and maintenance of equipment reliable as possible without having to worry about remembering to "wind up that timing relay". PS. Not having seen one of these wind up relays I suppose it would be possible for it to be automatically wound up again by a motor when power was restored. See http://www.automatictiming.com/pdf_atc/305E_data.pdf No manual "wind up" required. |
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Ross Herbert wrote:
PS. Not having seen one of these wind up relays I suppose it would be possible for it to be automatically wound up again by a motor when power was restored. They are used as hall lighting realys in apartment staircases. Press button, winds up, light on. Realease button, winds down... delay... lights out. Thomas |
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"Ross Herbert" wrote in message ... | Granted, such a device will work but it is hardly an elegant technical | solution. The whole idea of technology in industry is to make the | operation and maintenance of equipment reliable as possible without | having to worry about remembering to "wind up that timing relay". No, no 'remembering' required. When you apply power, the clock motor winds the mechanism up to the preset stop. When the power goes off, the spring unwinds until the switch actuates. Fully automatic. Also, the http://www.automatictiming.com product is far too complex. The ones I remember look like a small kitchen timer mounted on a bracket, and usually have a center screw to loosen to set the delay. Wish I could find a picture/web page. N |
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On Tue, 4 Jan 2005 22:42:13 -0800, DaveC wrote:
So the answer is... no. If power fails at the remote site, so does the control circuitry and its power. So a traditional delay relay won't work. The relay, powered by mains, simply opens the wireless sensor's sense circuit when power goes away. I just want it to do so after waiting a few minutes to see if power comes back on. The alarm isn't for security purposes, just for letting those responsible know that certain things have occurred, one of which is power fail. The sensor is a wireless device run on a lithium battery, and is a packaged deal so has no spare power available. The relay's not near the alarm CPU, so that power isn't available, either. Suggestions for a simple mains-powered circuit that will open a pair of contacts about 5 minutes after de-energizing? If it's to be battery-powered, it needs to be super-low drain. I rather keep battery replacements down to every 2 years, at most. An idea that just struck me: the presence of mains power could keep this circuit de-energized. When power fails, the battery is connected to the circuit which starts the countdown. When zero is reached (ie, 5 minutes have passed), a pair of contacts would open. And the energizing circuit (triggering these contacts) would only have to be a one-shot; once the alarm is triggered, the circuit could de-energize. That way the battery is utilized only briefly, during power-fail situations. --- Yes, that's the way I'd do it. --- How might I construct such a circuit? --- Depends... 1. How long does the relay have to stay ON/OFF to trigger the alarm? 2. Do you have to stay with the relays you're now using? 3. If you can change relays what are your limitations? That is, will the relays be used for alarm triggering only or will they also be doing something else in the non-alarm-triggering state? -- John Fields |
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"DaveC" wrote in message al.net... On Fri, 7 Jan 2005 16:07:32 -0800, DaveC wrote (in article et): Thanks for all the great ideas. All of this makes my (volunteer) job much easier. A new twist to the challenge: The output needs to be a one-shot, momentary-close event. In other words, 5 minutes after power fails, the contacts need to close and open again. This alerts the alarm to the power out-condition, and clears the alarm sense line for another event to be reported. Ideas? Use a 555 timer IC in a one-shot configuration. You could even use a 556 dual timer and use one for the 5 minute delay and the other for the pulse to close the relay. |
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On Sat, 08 Jan 2005 10:01:54 -0800, DaveC wrote:
On Fri, 7 Jan 2005 16:07:32 -0800, DaveC wrote (in article et): Thanks for all the great ideas. All of this makes my (volunteer) job much easier. A new twist to the challenge: The output needs to be a one-shot, momentary-close event. In other words, 5 minutes after power fails, the contacts need to close and open again. This alerts the alarm to the power out-condition, and clears the alarm sense line for another event to be reported. Ideas? Sure. Use the battery and charger and switch from an emergency light. Use the 6V or whatever to power a two-555 circuit, or for a more accurate five minutes, use a 4060. And you could use another output from the 4060 to turn itself off until power comes back on. Good Luck! Rich |
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On Fri, 7 Jan 2005 15:59:38 -0800, DaveC wrote:
On Fri, 7 Jan 2005 11:26:30 -0800, John Fields wrote (in article ): Depends... 1. How long does the relay have to stay ON/OFF to trigger the alarm? Tech support guy would check with the engineers on Monday, but... SWAG: 100 ms. A few (he wasn't willing to guess) microamps @ 3v 2. Do you have to stay with the relays you're now using? No. 3. If you can change relays what are your limitations? That is, will the relays be used for alarm triggering only or will they also be doing something else in the non-alarm-triggering state? Dedicated to alarm trigger only. --- OK, I posted a circuit for you on abse. If you need a circuit description let me know and I'll post one over there. -- John Fields |
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wrote:
In alt.engineering.electrical wrote: The 85 cent ones (CBC-125) are 1 F, 2.5 V. No, the CBC-125 is not the one I had in mind. I should have made it clearer. It is CBC-131, which is 85 cents in qty 10 and is .1 (point one) uf at 5 volts, not 1 uf at 2.5 volts. The CBC-125 is $1.00 each in qty 10 Ah. I need a newer (paper) All catalog - I wasn't checking their site. What I didn't know is implied in your next sentence: Some of these capacitors are made for very low current (microamps, CMOS memory) and not the tens to hundreds of milliamps you'd need for a relay or the 10-20 milliamps you'd need for an optoisolator or solid state relay. What happens if you place a 10 to 30 ma load on one of those caps? The voltage collapses. Another way to say what I said above is that the caps have a high internal resistance / impedance / ESR. As an example, look at pages 872 and 873 of the current Digi-Key catalog, T051. On 872 are the Cooper PowerStor capacitors. The "A" series has a 1 F 2.5 V cap with 0.090 ohm ESR (@ 1 KHz). DC will be different, but: if you charged one of these caps to 2.5 V and then shorted the leads, the initial current would be 2.5 / 0.09 or 28 A. The "B" series (what All sells) has a 1 F 2.5 V at 0.4 ohm ESR: 6.3 A. At the top left of page 873 are the Panasonic memory backup type capacitors. One is 1 F 5.5 V with 30 ohm ESR, or 180 mA max short circuit current. (As a fairer comparison with the Coopers, charging this one to only 2.5 V would yield an 83 mA short circuit current.) So, 10 to 30 mA might be doable with the memory backup capacitor, but not too much more. As is typical with OP's we may never hear how he makes out. I don't know... now he's trying to avoid falling down a well... Matt Roberds Matt, Thanks! Good info. I'm wondering what he is really trying to accomplish, too. I'll post the results I get, once the parts arrive. Ed |
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