# DC pulse from a mains load?

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Guest

Wed Dec 26, 2018 11:45 am

I’d like to find a simple way to get a DC pulse from close to a two or three wire mains cable by detecting whenever its 240V ac load is switched on.

If that is unachievable, what would then be the recommended simplest safe circuit after exposing the conductors please?

Guest

Wed Dec 26, 2018 12:45 pm

On Wednesday, December 26, 2018 at 9:40:47 PM UTC+11, terry...@gmail.com wrote:
Quote:
I’d like to find a simple way to get a DC pulse from close to a two or three wire mains cable by detecting whenever its 240V ac load is switched on.

If that is unachievable, what would then be the recommended simplest safe circuit after exposing the conductors please?

My guess would be that you would have to separate the live and neutral wires by enough to let you sense the current flowing in through the live wire and back through neutral wire.

In the space between the live and neutral wire you'd have an alternating magnetic field that you could sense with a Hall sensor.

http://www.farnell.com/datasheets/2354215.pdf

With this device you'd just get a (small) 50Hz voltage proportional to AC current through the wire, so you have to detect and rectify that and use it to generate your DC pulse. You'd have to find you own power supply to power the sensor and whatever did the signal processing.

It wouldn't be all that simple, but it would work.

--
Bill Sloman, Sydney

Klaus Kragelund
Guest

Wed Dec 26, 2018 12:45 pm

Mains wire goes through the toroid hole 😊

Klaus Kragelund
Guest

Wed Dec 26, 2018 12:45 pm

For a safe circuit, add a current transformer (could just be a toroid mains transformer). Then add a resistor on the high turns ratio winding to generate a voltage when the load is on

Rectify this voltage, add cap and you have a DC voltage when the load is on

Guest

Wed Dec 26, 2018 12:45 pm

terrypingm wrote
Quote:
I=E2=80=99d like to find a simple way to get a DC pulse from close to a two
or three wire mains cable by detecting whenever its 240V ac load is switched
on.

If that is unachievable, what would then be the recommended simplest safe circuit

Don't know how much you know about 'tronix,
you can do that with an old (I did) tape recorder playback head next to the power cable.
Add an opamp to amplify the picked up AC,
and rectify it with a diode
(use a dual opamp diode precision rectifier).
Then AC coupling and a one shot to make one pulse.
Power from a 9 V battery... lipo, wall wart, RTG, handcrank,
??

Position of the playback head relative to teh 3 wire cable needs some attention
(you want to be close to ONE a current carrying wire).

Terry Pinnell
Guest

Wed Dec 26, 2018 1:45 pm

<698839253X6D445TD_at_nospam.org> wrote:

Quote:
terrypingm wrote
I=E2=80=99d like to find a simple way to get a DC pulse from close to a two
or three wire mains cable by detecting whenever its 240V ac load is switched
on.

If that is unachievable, what would then be the recommended simplest safe circuit

Don't know how much you know about 'tronix,
you can do that with an old (I did) tape recorder playback head next to the power cable.
Add an opamp to amplify the picked up AC,
and rectify it with a diode
(use a dual opamp diode precision rectifier).
Then AC coupling and a one shot to make one pulse.
Power from a 9 V battery... lipo, wall wart, RTG, handcrank,
??

Position of the playback head relative to teh 3 wire cable needs some attention
(you want to be close to ONE a current carrying wire).

Thanks all, appreciate the fast replies.

Some fun experimenting is imminent ;-)

John Larkin
Guest

Wed Dec 26, 2018 5:45 pm

On Wed, 26 Dec 2018 03:03:01 -0800 (PST), Klaus Kragelund
<klauskvik_at_hotmail.com> wrote:

>Mains wire goes through the toroid hole ?

Just a pickup coil near the wires will sense current. No need to
disturb the power wiring.

A drum core inductor is a simple pickup.

--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Cursitor Doom
Guest

Wed Dec 26, 2018 7:45 pm

On Wed, 26 Dec 2018 11:26:14 +0000, 698839253X6D445TD wrote:

Quote:
Position of the playback head relative to teh 3 wire cable needs some
attention (you want to be close to ONE a current carrying wire).

You'd have to split the live and neutral by at least half an inch though
so they don't cancel each other out.

--
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John Larkin
Guest

Wed Dec 26, 2018 7:45 pm

On Wed, 26 Dec 2018 18:36:01 -0000 (UTC), Cursitor Doom
<curd_at_notformail.com> wrote:

Quote:
On Wed, 26 Dec 2018 11:26:14 +0000, 698839253X6D445TD wrote:

Position of the playback head relative to teh 3 wire cable needs some
attention (you want to be close to ONE a current carrying wire).

You'd have to split the live and neutral by at least half an inch though
so they don't cancel each other out.

Get a small coil, like a drum core inductor, connect it to an amp and
headphones, and walk around with it.

You can trace power wires inside walls. Lots of other interesting
sounds.

Similar fun with an amplified photodiode.

--

John Larkin Highland Technology, Inc trk

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

Guest

Wed Dec 26, 2018 8:45 pm

Cursitor Doomed
Quote:
On Wed, 26 Dec 2018 11:26:14 +0000, 698839253X6D445TD wrote:

Position of the playback head relative to teh 3 wire cable needs some
attention (you want to be close to ONE a current carrying wire).

You'd have to split the live and neutral by at least half an inch though
so they don't cancel each other out.

Nope, as you can see from the picture,
and in that setup I used it to measure current draw from a normal 2 wire mains lead,
Used for years.

film studio perfotape machines,
You could perhaps also use it to listen in on POTS telephone lines
without making physical contact,
Playback heads have a nice pointed sensitivity range

bitrex
Guest

Wed Dec 26, 2018 10:45 pm

On 12/26/2018 11:10 AM, John Larkin wrote:
Quote:
On Wed, 26 Dec 2018 03:03:01 -0800 (PST), Klaus Kragelund
klauskvik_at_hotmail.com> wrote:

Mains wire goes through the toroid hole ?

Just a pickup coil near the wires will sense current. No need to
disturb the power wiring.

A drum core inductor is a simple pickup.

A rectangular slab of copper-clad FR4 on ether side of the wire will
probably work OK as a pickup/sensor, it's cheap

bitrex
Guest

Wed Dec 26, 2018 10:45 pm

On 12/26/2018 04:05 PM, bitrex wrote:
Quote:
On 12/26/2018 11:10 AM, John Larkin wrote:
On Wed, 26 Dec 2018 03:03:01 -0800 (PST), Klaus Kragelund
klauskvik_at_hotmail.com> wrote:

Mains wire goes through the toroid hole ?

Just a pickup coil near the wires will sense current. No need to
disturb the power wiring.

A drum core inductor is a simple pickup.

A rectangular slab of copper-clad FR4 on ether side of the wire will
probably work OK as a pickup/sensor, it's cheap

Y'know, with wires soldered to it, naturally

Guest

Wed Dec 26, 2018 11:45 pm

onsdag den 26. december 2018 kl. 23.31.00 UTC+1 skrev Cursitor Doom:
Quote:
On Wed, 26 Dec 2018 18:47:24 +0000, 698839253X6D445TD wrote:

Playback heads have a nice pointed sensitivity range

Is that a xtal I see hiding under that grey goop?

Cursitor Doom
Guest

Wed Dec 26, 2018 11:45 pm

On Wed, 26 Dec 2018 18:47:24 +0000, 698839253X6D445TD wrote:

Quote:
Playback heads have a nice pointed sensitivity range

Is that a xtal I see hiding under that grey goop?

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Cursitor Doom
Guest

Wed Dec 26, 2018 11:45 pm

On Wed, 26 Dec 2018 18:47:24 +0000, 698839253X6D445TD wrote:

Quote:
Nope, as you can see from the picture,
and in that setup I used it to measure current draw from a normal 2 wire
Used for years.

Sounds like these heads could make good improvised current probes for
oscilloscopes. It took me ages to find a decent Tektronix 'scope current
probe and I had to pay through the nose for it, too.
For larger currents, though, I got some of these and they work -
surprisingly - really well!

https://www.ebay.co.uk/itm/SCT-013-030-Non-invasive-AC-Current-Sensor-
Clamp-Sensor-30A-Good/141679460958?
hash=item20fcc1025e:g:pGYAAOSwpDdVZ82w:rk:9:pf:0

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