Delay on a mains-powered relay?

See

No manual "wind up" required.

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

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

Thomas

| 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 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.

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,

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

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?

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.

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

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.

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

1K doesn't seem exceedingly small for a simple PDF - but I'm using Pan, which doesn't interpret inline PDFs either; this could be a configuration setting I haven't got to yet. So, yeah, it's probably the newsreader.

Cheers! Rich

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

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