Help with simple circuit please

Mr Sandman

unread,

Oct 15, 2012, 5:22:05 AM10/15/12

to

Hi all,

I've a novice with electronics, i think i understand al the principles and
roughly know what i may need, but putting it all together is the bit i need
help with!

What i am trying to do is make a power failure auto dialler. Basically i
will use a third party dialler as part of a burglar alarm which will be
triggered by closing a normally closed pair of terminals.
The scenario is i have a house in France and my neighbour watches over it,
but it is a bit remote so he cant check the security lights, freezers
heating etc to make sure the power hasn't tripped off etc.
But what i don't want to do is have the auto dialler call him needlessly nor
at an inconvenient hour....!
So it needs a timer to prevent the trigger being activated unless the power
has been off for more than two hours (just in case the power is only off for
a short period like during a storm), and some way of not triggering the auto
dialler unless its daytime.

All advice on how to approach this would be most welcome!

Cheers

Steve

Uwe Hercksen

unread,

Oct 15, 2012, 5:57:31 AM10/15/12

to

Mr Sandman schrieb:

> So it needs a timer to prevent the trigger being activated unless the
> power has been off for more than two hours (just in case the power is
> only off for a short period like during a storm), and some way of not
> triggering the auto dialler unless its daytime.

Hello,

and all electronics should be powered from an accumulator with enough
capacity for at least one full day of operation. Of course the telephone
should work also during a power off period. Not only the telephone of
your house, but also of the neighbour.

Bye

mike

unread,

Oct 15, 2012, 6:24:43 AM10/15/12

to

the details depend on exactly how the dialer is triggered, but basically...
Use a photocell to detect daylight.
Use a wall wart charging a cap with enough discharge time to
ignore short outages.
If the solar cell is up and the cap is discharged, activate the dialer.
Two hours is a stretch, but a lot depends on how long outages are.
Around here, it it's out for more than a few seconds, it's out for good.

Ian Malcolm

unread,

Oct 15, 2012, 8:10:44 AM10/15/12

to

mike <spa...@gmail.com> wrote in news:k5goa6$osa$1...@dont-email.me:

Since the O/P is an electronics novice, the use of an off-the-shelf 12V
time delay relay for the two hour delay + a 240Vac coil relay to trigger
it would probably be the best approach. Add a photocell module that
inhibits the input to the time delay relay during the hours of darkness,
a SLA float charger and a suitably sized SLA battery + the autodialler
and the job can be done with no more than simple wiring.

As long as the photocell is before the time delay, it wont alarm till two
hours after sunrise - otherwise it will be antisocially early in the
summer. It may be better to use an off-the-shelf central heating control
timer to implement the "not anti-social hours" function. Many have
enough internal backup to keep time for over 6 hours without mains power.

However, by the time all that lot is obtained, it might well be cheaper
and simpler to get a commercial mains failure and freezer monitoring
module with GSM that will text you with mains failure and restoration or
out of range freezer temperature events and ring the during civilised
hours neighbour yourself!
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & >32K emails --> NUL

TheQuickBrownFox

unread,

Oct 15, 2012, 9:14:26 AM10/15/12

to

http://tinyurl.com/8qq6pdd

snip

Ian Malcolm

unread,

Oct 15, 2012, 10:09:25 AM10/15/12

to

TheQuickBrownFox <thequick...@overthelazydog.org> wrote in
news:403o78pql3171kt7q...@4ax.com:

No, that doesn't have a volt free relay output that is easily accessible.
<http://preview.tinyurl.com/DIN-Timer>
is a far better choice.

Ian Malcolm

unread,

Oct 15, 2012, 10:14:15 AM10/15/12

to

Ian Malcolm <See.My.Sig...@totally.invalid> wrote in
news:XnsA0ED9A306C...@88.198.244.100:

>
> No, that doesn't have a volt free relay output that is easily
> accessible. <http://preview.tinyurl.com/DIN-Timer>
> is a far better choice.

... but it is ESSENTIAL to confirm that the module doesn't rely on mains
power to operate the relay. Some small timer modules use a latching relay
to save power and they would also work.

Joerg

unread,

Oct 15, 2012, 2:18:43 PM10/15/12

to

A convenient option would be this plus a netbook or some other computer
that offers many hours of battery runtime:

http://labjack.com/u3

Then it's all programmable and there is a light version of the necessary
software that usually comes with these. At least it came with mine.

--
Regards, Joerg

http://www.analogconsultants.com/

mike

unread,

Oct 15, 2012, 3:22:25 PM10/15/12

to

On 10/15/2012 11:18 AM, Joerg wrote:
> Mr Sandman wrote:
>> Hi all,
>>
>> I've a novice with electronics, i think i understand al the principles
>> and roughly know what i may need, but putting it all together is the bit

>> i need help with!u

>>
>> What i am trying to do is make a power failure auto dialler. Basically
>> i will use a third party dialler as part of a burglar alarm which will
>> be triggered by closing a normally closed pair of terminals.
>> The scenario is i have a house in France and my neighbour watches over
>> it, but it is a bit remote so he cant check the security lights,
>> freezers heating etc to make sure the power hasn't tripped off etc.
>> But what i don't want to do is have the auto dialler call him needlessly
>> nor at an inconvenient hour....!
>> So it needs a timer to prevent the trigger being activated unless the
>> power has been off for more than two hours (just in case the power is
>> only off for a short period like during a storm), and some way of not
>> triggering the auto dialler unless its daytime.
>>
>> All advice on how to approach this would be most welcome!
>>
>
> A convenient option would be this plus a netbook or some other computer
> that offers many hours of battery runtime:
>
> http://labjack.com/u3
>
> Then it's all programmable and there is a light version of the necessary
> software that usually comes with these. At least it came with mine.
>

An interesting solution would use a palm pilot PDA.

If you're gonna use a laptop, just run BBS software on it
and use the internal modem to do the dialing.
And you could dial in any time to check status or download
images captured by a webcam.
There's probably freeware available to do just that if you
have a data connection. Cobbling together some BBS software
would save the cost of an ISP.

TheQuickBrownFox

unread,

Oct 15, 2012, 10:02:20 PM10/15/12

to

On Mon, 15 Oct 2012 14:09:25 +0000 (UTC), Ian Malcolm

<See.My.Sig...@totally.invalid> wrote:

>TheQuickBrownFox <thequick...@overthelazydog.org> wrote in
>news:403o78pql3171kt7q...@4ax.com:
>
>> On Mon, 15 Oct 2012 12:10:44 +0000 (UTC), Ian Malcolm
>> <See.My.Sig...@totally.invalid> wrote:
>
>>>
>>>Since the O/P is an electronics novice, the use of an off-the-shelf 12V
>>>time delay relay for the two hour delay + a 240Vac coil relay to trigger
>>>it would probably be the best approach.
>>
>> http://tinyurl.com/8qq6pdd
>>
>
>No, that doesn't have a volt free relay output that is easily accessible.
><http://preview.tinyurl.com/DIN-Timer>
>is a far better choice.

He could use either and a UPS and a battery bank. No solar, no
worrying.

Just fire up the ups on the charge side long enough to top off the
batteries a couple times a day, and whenever there is an outage on the
controlled line, the UPS turns on and takes up the slack and sends a flag
email.Check it for correct function and charge level once a month. Voila.

Mr Sandman

unread,

Oct 16, 2012, 3:04:34 AM10/16/12

to

>>
>>Since the O/P is an electronics novice, the use of an off-the-shelf 12V
>>time delay relay for the two hour delay + a 240Vac coil relay to trigger
>>it would probably be the best approach.
>
> http://tinyurl.com/8qq6pdd
>

No, that doesn't have a volt free relay output that is easily accessible.
<http://preview.tinyurl.com/DIN-Timer>
is a far better choice.

Thanks, that looks like a good solution for the sociable hours side of the
problem! I could program it so that it keeps the contacts closed during the
night and run a power outage sensor circuit in parallel with it, so that if
the power outage circuit has triggered(ie the power has been off for more
than two hours and it has opened its contacts) it will trigger the auto
dialler.

Sorted! Well now is just the design of a simple circuit that will trigger
when the power has been out for two hours.....will a simple rc circuit have
enough of a delay with a reasonable sized capacitor?

Steve

Uwe Hercksen

unread,

Oct 16, 2012, 6:58:40 AM10/16/12

to

Mr Sandman schrieb:

> Sorted! Well now is just the design of a simple circuit that will
> trigger when the power has been out for two hours.....will a simple rc
> circuit have enough of a delay with a reasonable sized capacitor?

Hello,

two hours are too long for a rc circuit. If you use a large resistor and
a large electrolytic capacitor you will get problems with the leakage
current of this capacitor.

Bye

unread,

Oct 18, 2012, 11:27:45 AM10/18/12

to

On Wed, 17 Oct 2012 12:18:14 -0500, John Fields
<jfi...@austininstruments.com> wrote:

>On Tue, 16 Oct 2012 18:53:33 +0100, "Mr Sandman"
><san...@ntlworld.com> wrote:
>
>>
>>
>>"John Fields" wrote in message
>>news:9egq7898cl3v9s5ns...@4ax.com...

>>Would you like a schematic?
>
>Hi John, yes I'd love a schematic of your suggestion!
>
>Many thanks
>
>steve
>
>---
>OK, I'll have something for you later on today or tomorow.

---
Steve,

I've posted some files to abse for you:

news:4h6088p91t7bj1iu6...@4ax.com

a PDF schematic of something you can actually build, an LTspice
simulation showing that it probably works in real life, and some
support files for the sim.

Download all of the files into a single folder and click on the .asc
file to view the sim schematic and later run it.

I'm assuming you have LTspice...

The PDF shows a 7555 astable running at about 1Hz for the clock, and
another one - a one-shot - on the output. By selecting the values of
Ct and Rt you can adjust the length of the output pulse in order to
satisfy the dialer's requirements; T = 1.1RtCt.

Also, you may have to connect the 7555's output to a transistor if the
dialer is looking for an open collector to drive it, or through a
transistor to a relay if it needs contact closure.

If you need a circuit description, let me know and I'll write one up
for you.

--
JF

unread,

Oct 19, 2012, 2:39:10 AM10/19/12

to

"Mr Sandman" wrote in message
news:L-2dnWecbdFBcx3N...@brightview.co.uk...

Oops top posted, apols. Reposted here-

John Fields

unread,

Oct 22, 2012, 10:00:46 AM10/22/12

to

On Fri, 19 Oct 2012 07:39:10 +0100, "Mr Sandman"
<san...@ntlworld.com> wrote:

>A description of the workings will certainly help with my learning so yes
>please John!

---
I've posted a new schematic and a circuit description for you at abse
under "Dialer timer".

>Many thanks for taking the time to help us out with this!

---
My pleasure!

BTW, I forgot to mention that in order to run the circuit in dark mode
set V4 Trise to 20ms, and for daylight mode, 10ms.

You can get a pretty good picture of what's happening by probing V4,
U2-Q6, and U7-OUT.

--
JF

Mr Sandman

unread,

Oct 22, 2012, 11:47:26 AM10/22/12

to

"John Fields" wrote in message

news:2oia88d6oo4lh832o...@4ax.com...

Thanks John, but i cant see alt.binaries.schematics.electronic from my isp,
can you post it somewhere else too?

Many thanks!

Steve

John Fields

unread,

Oct 22, 2012, 1:45:14 PM10/22/12

to

On Mon, 22 Oct 2012 16:47:26 +0100, "Mr Sandman"
<san...@ntlworld.com> wrote:

>Thanks John, but i cant see alt.binaries.schematics.electronic from my isp,
>can you post it somewhere else too?
>
>Many thanks!
>
>Steve

---
Sorry, no.

I tried emailing it to you, but your ISP refused it.

What next?

--
JF

John Fields

unread,

Oct 22, 2012, 2:21:52 PM10/22/12

to

---
Here:

http://s1339.photobucket.com/albums/o704/jfieldsataustinintrumentsdotcom/?action=view&current=DialerTimer3_zps6595ce04.jpg
--
JF

John Fields

unread,

Oct 22, 2012, 2:31:12 PM10/22/12

to

On Mon, 22 Oct 2012 13:21:52 -0500, John Fields

Here's how it works:

First, there are two modes of operation: daylight mode, which is
entered if the mains failure occurs during the day, and night mode, if
the failure occurs at night.

U1 is a 7555 timer configured as an astable multivibrator, and it
generates 1MHz square waves used as clocks for the simulation; in real
life it would output 1Hz clocks.

S1 and S2 simulate a mains operated form "C" (SPDT) relay with the NC
contact connected to GND and the NO contact connected to +12. Thus,
when the mains is hot, the NO contact will made, forcing RST high and
resetting the circuit. If the mains should fail, however, the
armature will be released and the NO contact will be made, forcing RST
low and de-asserting the reset.

Assuming daylight mode, U5+ will have gone more positive than U5-,
forcing U5's output and U6A's PREset input high, which will also force
U6A-Q, U6B-D, and one of U3D's inputs high.

In the meantime, RST's having been high had disabled U2 by keeping it
in reset mode, but RST's going low when the mains failed forced U2 out
of reset, allowing it to count up.

U2 is used as a 2 hour timer for this application, and by accumulating
1 second clocks from U1, will reach 2 hours when it counts up to 7200.

7200 in Hexadecimal is 1C20, which in binary is 0001 1100 0010 0000.

U2 is a 14 stage ripple counter, and its outputs map to binary 7200
like this:

Q14 Q13 Q12 Q11 Q10 Q09 Q08 Q07 Q06 Q05 Q04 Q01

0 1 1 1 0 0 0 0 1 0 0 0 .

That means that when the count has reached 7200, Q13,Q12,Q11, and Q6
will be high and all the other outputs will be low.

U3A, U3B, and U3C are used to decode the output data from the counter,
with the output of U3C going high when the count reaches 7200.

When that happens,the output of U4C will go low, forcing U1 into reset
and stopping the clocks.

Also, remembering that we're working in daylight mode and that since
U6B-D is being held high, when U3C goes high it'll be used as the
clock input of U6B which will force U6B-Qbar permanently low until the
mains is restored and RST is once again asserted.

The falling edge of U6B-Qbar is differentiated by C3 and used as a
low-going trigger for U7, a 7555 timer used as a one-shot to provide
an output to the dialer.

In night mode, RST will go low when a mains failure occurs, but U5's
output will be low because no light has yet been detected.
RST going low at one of U4B's inputs forces U2's reset input low,
allowing U2 to count. as before, U2 will count up to 7200, but since
it's dark out we want to postpone the output to the dialer for 2 hours
after first light.

To do so, the counter's output is again decoded at 7200 clocks,
inverted by U4C, and sent to U1's reset input which will stop the
clock.

The circuit will remain in this condition until first light is
detected and U6A-Q goes high.

Since stopping the clock has kept the counter's outputs at 7200
binary, U3C's output will remain high and U6A-Q going high will cause
U3D to go high. That high-going edge will be differentiated by C1 and
used to reset U2.

When that happens, U3C's outputs will all go low, as will the output
of the decoder, forcing U4C's output high, enabling U1, allowing it to
start making clocks.

U2 will now start counting clocks again and when it gets to 7200 will
cause U1 to be reset, stopping the clocks, and also sent to the clock
input of U6B.

Now, since U6A-Q is high because first light has been detected, when
the clock input of U6B goes high U6B-Qbar will go low, triggering U7
and providing an output for the dialer.

So, in summary:

Daylight mode causes the counter to count to 7200 once and then
trigger the one-shot.

Night mode causes the counter to count to 7200, then freeze
until first light is detected when it'll be reset and will count to
7200 again before triggering the one-shot.

--
JF

Mr Sandman

unread,

Oct 22, 2012, 2:07:05 PM10/22/12

to

"John Fields" wrote in message

news:g20b88dhgfobtp0do...@4ax.com...

I am working on a way to access abse...will see how i get on and let you
know.

Cheers chap

Steve

Mr Sandman

unread,

Oct 23, 2012, 2:07:40 AM10/23/12

to

Thanks very much John!
I will have a look though the description and have a play with ltspice
today...its well beyond my design skills!

Thanks again

Steve

Rick

unread,

Oct 23, 2012, 6:59:05 AM10/23/12

to

"John Fields" <jfi...@austininstruments.com> wrote in message
news:4v3b881ri9mj5m7a6...@4ax.com...

You will need some hysteresis around the "first light sensor", U5. The set
and reset inputs of the CD4013 (U6A) do not like slow moving signals.

John Fields

unread,

Oct 23, 2012, 9:51:18 AM10/23/12

to

On Tue, 23 Oct 2012 05:59:05 -0500, "Rick" <rik...@bellsouth.net>
wrote:

>You will need some hysteresis around the "first light sensor", U5. The set
>and reset inputs of the CD4013 (U6A) do not like slow moving signals.

---
Since the specs for the rising edge rates of SET and RESET are only
relevant when the time between SET or RESET and Q or Qbar is
important, the edge rate of U5's output doesn't matter.

What does matter is that at some point along U5's 0 to 12V output, U6A
will be forced to latch, and when that happens U6A will stay latched
until the mains goes hot.

--
JF

ehsjr

unread,

Oct 23, 2012, 3:08:10 PM10/23/12

to

Wow, you really put in a lot of extra effort to post it there
as well as ABSE.

Nice. As usual, from you. :-)

Ed

unread,

Oct 24, 2012, 4:29:28 PM10/24/12

to

On Wed, 24 Oct 2012 18:04:37 +0100, "Mr Sandman"
<san...@ntlworld.com> wrote:

>Thanks John,
>
>I copied and pasted the above and converted the font to a fixed width but
>its still gibberish for some reason in word. I am using Lucinda console
>font which is apparently fixed width.

---
You shouldn't have to do any of that if you've got your newsreader
configured to display incoming posts in a fixed pitch font.

There's also a problem in that your newsreader isn't quoting properly,
making it impossible to reply to you without some really inconvenient
machinations on my end.
---

>Can you describe the circuit for me?

---
Yes, of course, but you should learn how to read pictures before
asking someone to waste a thousand words.
---

>Cant seem to source them in the UK for a reasonable price... will these do-
>
>http://www.ebay.co.uk/itm/290598992722

---
No manufacturer?
No data sheet?
Question marks after the important specs?

I sure wouldn't go for it.
---

>I will have to mount these remotely, say 20' away from the main circuit in
>order to get a good source of daylight.

---
OK, if what you mean is the entire detector circuit.
---

>I may have to shade it from direct
>light too just in case a bright moonlight is interpreted as daylight....;-)

---
One bridge at a time...

--
JF

SoothSayer

unread,

Oct 24, 2012, 6:52:57 PM10/24/12

to

You know, I have seen this "view with a fixed pitch font" from you
several times in the past, and in reflection each time was when you were
posting a circuit or a fix for someone.

So, essentially, Larkin is full of shit. You have been a greater
contributor to the group both in the spirit of the industry and the
spirit of the group topic.

He magically lost track of the circuits I posted too, but keeps
claiming I have never posted any, and keeps asking for more.

Don't know who put the burr under his saddle, but folks here seem to
bear the brunt of the resultant effect of his bent affect.

Reminds me of Rodney King. May he rest in piece. The idiots gave
Arafat the Nobel Prize that year.

Mr Sandman

unread,

Oct 25, 2012, 2:58:03 AM10/25/12

to

"John Fields" wrote in message

news:l1ig88drp8f02kkiv...@4ax.com...

unread,

Oct 26, 2012, 10:26:17 AM10/26/12

to

---
Vcc, actually, but yes.

With a 50mA load, the 7555 drops about 2V across its output, so if you
choose a relay with a coil current less or equal to that, a 7555
should work OK.

A perfect fit would be an OMRON G5V-1-DC12:
http://www.components.omron.com/components/web/pdflib.nsf/0/EB5C8B538D0F639485257201007DD57D/$file/G5V_1_0911.pdf

Farnell has them in stock, and don't forget to put a diode (a
1N914/1N4148 will do) across the coil, with the cathode connected to
the pin going to U7-3.

Just as an aside, I think you're going to have a tough time sourcing
K1 if it's got to have a 240VAC coil and signal level contacts, so one
solution would be to use a lower voltage DC coil relay and drive it
from a full-wave bridge fed by a capacitor in series with the mains,
like this: (Don't forget the fixed-pitch font ;)

MAINS>--[CAP]--+------------+
|K |A
[DIODE] [DIODE]
| |
+---[COIL]---+
| |
[DIODE] [DIODE]
|K |A
MAINS>---------+------------+

If you were to use the 24V coil version of the 12V OMRON relay, that
would be the G5V-1-DC24, which has a 3840 ohm coil and a coil current
of 6.25mA with 24V across the coil.

Sooo...

Here's the fun part; how do we figure out the value of the cap?

Since the diode drops are insignificant, we can look at the circuit
like this:

MAINS>-----+--->240V/50Hz
|
[CAP]
|
+--->34VP
|
[COIL]
|
MAINS>-----+

Since the coil is seeing full-wave rectified AC instead of pure DC,
its RMS value must be equal to 24VDC, which means its peak value is
24VDC * sqrt2 ~ 34VP.

We also know that the coil will be drawing 6.25mA so, since in a
series circuit the current is everywhere the same, that 6.25mA must
also pass through the cap.

For that to happen, the impedance of the entire circuit must be:

E 240V
Z = --- = ---------- = 38400 ohms.
I 0.00625A

Now, since:

Z² = X² + R²

and we want to solve for the capacitance, we first need to get the
capacitive reactance, so we rearrange and solve for X:

Xc = sqrt (Z² - R²) ~ 38208 ohms.

Then, to get the capacitance:

1 1
C = ------------ = -------------------------- ~ 8.3E-8F
2pi f (Xc) 6.28 * 50Hz * 38208 ohms

That's 83nF.

82nF is the closest standard value, and Panasonic has a nice part,
ECQ-E6683JF:

http://industrial.panasonic.com/www-data/pdf/ABD0000/ABD0000CE23.pdf

Since the proof is in the pudding:

Version 4
SHEET 1 880 680
WIRE -32 -16 -224 -16
WIRE 112 -16 -32 -16
WIRE -224 32 -224 -16
WIRE -32 32 -32 -16
WIRE 112 32 112 -16
WIRE -32 160 -32 96
WIRE 0 160 -32 160
WIRE 112 160 112 96
WIRE 112 160 80 160
WIRE -224 208 -224 96
WIRE -32 224 -32 160
WIRE 112 224 112 160
WIRE -224 352 -224 288
WIRE -32 352 -32 288
WIRE -32 352 -224 352
WIRE 112 352 112 288
WIRE 112 352 -32 352
WIRE -224 400 -224 352
FLAG -224 400 0
SYMBOL res 96 144 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 3840
SYMATTR SpiceLine ""
SYMBOL diode -48 224 R0
WINDOW 0 -43 33 Left 2
WINDOW 3 -75 65 Left 2
SYMATTR InstName D3
SYMATTR Value 1N4148
SYMBOL diode 96 32 R0
WINDOW 0 46 34 Left 2
SYMATTR InstName D2
SYMATTR Value 1N4148
SYMBOL diode 128 288 R180
WINDOW 0 -48 33 Left 2
WINDOW 3 -77 0 Left 2
SYMATTR InstName D4
SYMATTR Value 1N4148
SYMBOL diode -16 96 R180
WINDOW 0 50 33 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D1
SYMATTR Value 1N4148
SYMBOL voltage -224 192 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value SINE(0 340 50)
SYMATTR Value2 ""
SYMATTR SpiceLine ""
SYMBOL cap -240 32 R0
SYMATTR InstName C1
SYMATTR Value 82n
SYMATTR SpiceLine ""
TEXT -210 376 Left 2 !.tran .2

Pay no attention to the ground connection, it's not needed (or
desired) for your application, but LTspice needs it for a 0 volt
reference.

--
JF

John Fields

unread,

Oct 26, 2012, 11:11:26 AM10/26/12

to

On Fri, 26 Oct 2012 11:19:25 +0100, "Mr Sandman"
<san...@ntlworld.com> wrote:

>Hi John,
>
>one other question is the schematic correct on abse regarding the cd4082,
>should this be cd4081?
>
>cheers
>
>steve

---
Good catch!

It should be a CD4081B and all the other logic should carry the 'B'
suffix as well.

--
JF

John Fields

unread,

Oct 27, 2012, 5:24:44 AM10/27/12

to

---
Oops...

I forgot about the 24V relay's inductance, which is about 6.6 henrys
with the armature down.

So instead of:

.MAINS>--[CAP]--+-----------+
. |K |A
. [DIODE] [DIODE]
. | |
. +--[3840R]--+
. | |
. [DIODE] [DIODE]
. |K |A
.MAINS>---------+-----------+

we have:

.MAINS>--[CAP]--+--------------------+
. |K |A
. [DIODE] [DIODE]
. | |
. +--[3840R]--[6.6H]--+
. | |
. [DIODE] [DIODE]
. |K |A
.MAINS>---------+-------------------+

and here's the reworked math:

Xl = 2pi f L = 6.26 * 50Hz * 6.6H = 2072 ohms

E 240V
Z = --- = --------- = 38400 ohms
I 0.00625A

Z² = R² + (Xl - Xc)²

Z² - R² = (Xl - Xc)²

38400² - 3840² = (2072 - Xc)²

sqrt(38400² - 3840²) = sqrt(2072 - Xc)²

38208 = sqrt(2072 - Xc)²

38208 + 2072 = 40280

38208 = sqrt(2072 - 40280)²
\
38208 = 38208 Xc

1 1
C = ---------- = -------------------------- 7.8E-8F = 78nF
2pi f Xc 6.28 * 50Hz * 40280 ohms

Closest E24 value is 75nF, and I'd use a Vishay BFC238332753:

http://www.vishay.com/docs/28124/mmkp383.pdf

--
JF

John Fields

unread,

Oct 27, 2012, 12:22:18 PM10/27/12

to

On Sat, 27 Oct 2012 04:24:44 -0500, John Fields
<jfi...@austininstruments.com> wrote:

<SNIP>

OMRON reports that if their G5V-1 relays are operated with the coil
energized for a long time and no switching is done, the heat from the
coil affects the insulation and causes a film to be deposited on the
contacts which can lead to problems.

Solution? Ditch the relay.

New schematic at abse.

--
JF