DC pulse from a mains load?

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 switch ed on.

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

Terry, East Grinstead, UK

Reply to
terrypingm
Loading thread data ...

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

Reply to
Klaus Kragelund

Mains wire goes through the toroid hole ?

Reply to
Klaus Kragelund

On Wednesday, December 26, 2018 at 9:40:47 PM UTC+11, snipped-for-privacy@gmail.com wr ote:

wo or three wire mains cable by detecting whenever its 240V ac load is swit ched on.

circuit after exposing the conductors please?

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

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

formatting link

With this device you'd just get a (small) 50Hz voltage proportional to AC c urrent 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
Reply to
bill.sloman

terrypingm wrote

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).

formatting link

Reply to
<698839253X6D445TD

Thanks all, appreciate the fast replies.

Some fun experimenting is imminent ;-)

Terry, East Grinstead, UK

Reply to
Terry Pinnell

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 
 Click to see the full signature
Reply to
John Larkin

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

--
This message may be freely reproduced without limit or charge only via  
the Usenet protocol. Reproduction in whole or part through other  
 Click to see the full signature
Reply to
Cursitor Doom

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 
 Click to see the full signature
Reply to
John Larkin

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, output to ADC. Used for years.

The trick comes from adjusting amplifiers for tape heads in 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

formatting link

Reply to
<698839253X6D445TD

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

Reply to
bitrex

Y'know, with wires soldered to it, naturally

Reply to
bitrex

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!

formatting link

--
This message may be freely reproduced without limit or charge only via  
the Usenet protocol. Reproduction in whole or part through other  
 Click to see the full signature
Reply to
Cursitor Doom

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

--
This message may be freely reproduced without limit or charge only via  
the Usenet protocol. Reproduction in whole or part through other  
 Click to see the full signature
Reply to
Cursitor Doom

looks like a tape head

Reply to
Lasse Langwadt Christensen

If the power wires aren't shielded, like in a conduit, an electrostatic pickup is fine. Wrap an insulated wire around the power conductors. Some oscilloscopes do that to pick off the line trigger.

I have seen an instrument that clamped the hot/black wire against a PC board to get the line trigger without making a direct line connection.

formatting link

But if the OP wants to sense a load, he needs to measure current, so needs a magnetic pickup.

--
John Larkin   Highland Technology, Inc   trk 

jlarkin att highlandtechnology dott com 
 Click to see the full signature
Reply to
John Larkin

You missed the point, Panteltje used a audio tape recorder head to sense current through a wire, he then amplified the signal. I believe he also said he just ran the unseparated pair (white wire pair) near the head and because the head response area is quite small it responds to the closest wire without any problem from the second wire. As he explained it, "a nice pointed sensitivity range" Probably should start saving audio heads, I think they're use may be dwindling. Mikek

Reply to
amdx

I thought the 'C' shaped thing around the blue resistor was the actual current sensor? Maybe Jan will deign to inform us in due course.

--
This message may be freely reproduced without limit or charge only via  
the Usenet protocol. Reproduction in whole or part through other  
 Click to see the full signature
Reply to
Cursitor Doom

On a sunny day (Wed, 26 Dec 2018 22:26:37 -0000 (UTC)) it happened Cursitor Doom wrote in :

Good price! is it not simpler to show the link as:

formatting link
then nobody has to be scared of alien website redirects.

the /itm/xxxxx where xxx is the item number.

As to the playback head, yes, but remember the induced voltage goes up with frequency etc. You will likely need some correction (like in a tape playback amplifier) I think I played with that,

We used a signal generator with a single wire in front of the head to calibrate the playback amplifier frequency correction for the perfotapes. Had to be done every now and then. Sixties.

The reason the wire is glued in position is, think of the width of a stereo head track, fraction of a cassette tape width.

I do not have all those expensive things or antiques like some here, technology had advanced, yes I used Avo in the past, but never longed back. Well I still have my old Trio analog scope from the seventies, it still works.

Reply to
<698839253X6D445TD

On a sunny day (Wed, 26 Dec 2018 22:30:56 -0000 (UTC)) it happened Cursitor Doom wrote in :

No, that is the head, the 'grey goop' is 2 compoment glue to prevent the wire from moving.

Reply to
<698839253X6D445TD

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.