"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

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.

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.

k, then yeah the brit guy above pointing toward the time delay relays
might be a way to go...

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

"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

"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.

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

"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.

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.

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.

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.

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

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,

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

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

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 .

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!