Delay on a mains-powered relay?

[Zak]

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

 

[NSM]

| 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

 

[John Fields]

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?

 

[DaveC]

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.
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
[email protected]
This is an invalid return address
Please reply in the news group

 

[DaveC]

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,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
[email protected]
This is an invalid return address
Please reply in the news group

 

[[email protected]]

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:

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

 

[DaveC]

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?
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
[email protected]
This is an invalid return address
Please reply in the news group

 

[James Sweet]

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.

 

[Rich Grise]

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

 

[John Fields]

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


Dedicated to alarm trigger only.

 

[DaveC]

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, I'm having trouble downloading it. The file is 1K, which looks
suspiciously small. Can you retrieve it?... it might just be my newsreader.
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
[email protected]
This is an invalid return address
Please reply in the news group

 

[[email protected]]

In alt.engineering.electrical [email protected] wrote:



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

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

 

[John Fields]

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.

 

[Rich Grise]

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.

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

 

[[email protected]]

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.

 

[[email protected]]

The parts arrived. I tested the 1 farad/RLY-635
circuit and it yields 4 minutes,45 seconds. + or -
measurement error.

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

 

[NSM]

....
| 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

 

[John Fields]

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.

---
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

 

[[email protected]]

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.

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

 

[[email protected]]

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?

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