Delay on a mains-powered relay?

They are used as hall lighting realys in apartment staircases. Press button, winds up, light on.

Realease button, winds down... delay... lights out.

Thomas

On Fri, 7 Jan 2005 11:26:30 -0800, John Fields wrote (in article ):

Tech support guy would check with the engineers on Monday, but... SWAG: 100 ms. A few (he wasn't willing to guess) microamps @ 3v

No.

Dedicated to alarm trigger only.

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Thanks for all the great ideas. All of this makes my (volunteer) job much easier.

See a new thread I started regarding sensing switch closure during power failure.

Thanks again,

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| 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

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

On Fri, 7 Jan 2005 16:07:32 -0800, DaveC wrote (in article ):

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?

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Ah. I need a newer (paper) All catalog - I wasn't checking their site.

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.

I don't know... now he's trying to avoid falling down a well...

Matt Roberds

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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.

much

5

line

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.

On Sat, 8 Jan 2005 15:06:53 -0800, John Fields wrote (in article ):

John, I'm having trouble downloading it. The file is 1K, which looks suspiciously small. Can you retrieve it?... it might just be my newsreader.

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I can retrieve it.  Send me your email address and I'll email you the
schematic.

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

The parts arrived. I tested the 1 farad/RLY-635 circuit and it yields 4 minutes,45 seconds. + or - measurement error. I connected the open points of the relay in series with a 1.5 volt battery driven analog clock and measured the time that way. Did it 3 times. Don't know how accurate the clock is, but it agrees with my wristwatch, and precision was not important in any event.

I still have to test with the other relays - I ordered & received RLY-639 and RLY-405 but haven't tested them yet, or the opto idea. The 639 and 405 relays should not last nearly as long - they have

145 ohm coils, while the 635 has a 500 ohm coil. I have the .1 farad caps, the opto and the relays, so testing now is just a matter of time. I realise the op has changed his request, so this is just follow up, but I'll post the results when I can.

Thanks for posting the results! As you noted, the original poster has moved on, but I might use something like this in a UPS I'm designing.

Basically, I want to switch from AC to battery at the slightest hint of a problem, but once AC comes back, I want it to have stayed on for some amount of time before I switch from battery to AC. I'm not too worried about the exact time, just as long as it meets a minimum. There will be a big cap in there someplace to handle the switching glitches.

This is for holding up a cable modem and VoIP box during power outages. I know I could just buy a commercial UPS and plug in the wall-warts, but it seems wasteful to me to go from 12 V DC to 120 V AC back to 12 V DC. Besides, for what I pay for a UPS, I can buy a bigger battery and a couple of support parts that will keep me up much longer than the UPS will.

Followups to s.e.design.

Matt Roberds

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Unless you have some overriding need for the delay when the mains come
back on again, why not just do something like this:

         BATTERY
         +-----+
         |    +|---+--------->VOUT+ TO EQPT
         |     |   |     
         |    -|---|-----+--->VOUT- TO EQPT
         +-----+   |     |
                   |     |
         +-----+   |     |
MAINS>---|~   +|---+     |    
         |     |         |
MAINS>---|~   -|---------+    
         +-----+  
         CHARGER

.... | This is for holding up a cable modem and VoIP box during power outages. | I know I could just buy a commercial UPS and plug in the wall-warts, but | it seems wasteful to me to go from 12 V DC to 120 V AC back to 12 V DC. ....

Use the UPS. It's not wasteful and it's way cheaper than do it yourself.

N

I tested with both the RLY-405 and the RLY-639 parts. Both of them last for 4 minutes. I was surprised to see them last so long, untl I looked at the datasheet. I tested each 3 times - same results. Those relays have polarity sensitive coils. They energize at a little over 2.5 (as measured) volts as the voltage on the cap rises while it charges. They stay energized until it drops to about .45 volts, per the datsheet, which accounts for the longer than anticipated period.

After the relays, I set out to test the opto - and realized I have no clue as to how to test it, without knowing what the sense loop specs are. I would welcome some ideas! I figure the sense loop must be very low current, because the OP said it runs on a lithium battery. And he indicated he wanted to keep battery replacement of any added battery to once. every two years, which implies that the lithiums last that long.

Ed

Two relays, two capacitors, one resistor. Refer to the circuit mentioned in my post above - a 5.5 super cap and RLY-639 or RLY-405. When power drops, the relay stays energized for ~4 minutes, then drops.

Use one of the closed points on the first relay to complete the circuit to a second relay from a charged cap. One point of the second relay is the output. Another point of the second relay to switch a low value resistor across the cap that energizes the second relay. Here's the circuit: (the output point is not shown)

A +-----0 \---relay2coil---+ | R1P(nc) | +---/\/\/\---o \--+ | | R1 R2P | | Cap2 | | | | | B +-----------------+------+

• 5 volts is supplied to point A, ground is at point B. R1P is the normally closed point of the relay mentioned in my earlier post and shown in the diagram below. R2P is one of the normally open points of relay 2. The other normally open point of relay 2 is the output you need.

Here's the ~4 minute delay circuit:

A -----+---relaycoil1----+ | | SuperCap | | | B -----+-----------------+

The super cap is a 1 farad 5.5 volt cap and the relay is RLY-639, both specified in the earlier post, from Allelectronics. Use a regulated 5 volt supply with series diode protection, or a regulated 6 volt supply with two 1N4001 diodes in series to produce the supply to points A and B. The diode protection prevents discharge of the capacitors back into the supply. Cap2 does not need to be a super cap. On an untested guess, I'd say a 470 uf cap with a second RLY-639 would work. A 100 ohm 1 watt resistor will work for R1 with that cap. Let me know if you want me to test it - I have the parts.

Ed

This is a better idea than mine and avoids switching glitches. The only thing I wonder about is the charger voltage. To float a 12 V gel cell I need 13.65 V or so charging voltage. Right now, the cable modem has a

12 V, 1 A wall wart, most likely linear, probably unregulated, so the "extra" 1.65 V may not be such a big deal. The VoIP box might have a switcher, so its voltage input might be more critical. I could do something like this:

MAINS>------------------------+ Relay | MAINS>---------------======---+ +--/ --+ BATTERY | | +-----+ | | | +|---++---A--+->VOUT+ TO EQPT | | | | -|---|-----+--->VOUT- TO EQPT +-----+ | | | | +-----+ | | MAINS>---|~ +|---+ | | | | MAINS>---|~ -|---------+ +-----+ CHARGER

Component "A" limits the voltage when the mains are on. It might be as simple as a diode or two in series, or as fancy as a voltage regulator. The relay contacts are held open by the mains, to keep the voltage to the equipment down. When the mains fail, the contact opens and the equipment gets whatever the battery voltage is. (I am less worried about what happens when the equipment has a lower-than- spec input voltage, but I will test it.)

Thanks!

Matt Roberds

Please note that all unregulated wall warts have a higher output voltage than the rated valus, even at *full rated current* (!!). Therefore, the output is far in excess of "rating" at lesser loads. In fact, to prevent damaging a radio i have, i use a "4.5V" wall wart to supply the 6V the radio needs.