How could you sense current in an AC power cord?

[William At MyBlueRoom]

I'm looking to detect if an AC power cord has current flowing through it. I'm not looking to measure how much current is flowing, simply that current greater than 2amps is flowing. Would wrapping a few turns of wire around the power cord work and what sort of circuit would be required?

Problems
1. I want inductive or hall effects sensors.
2. No modification of the original power cord in any way.
3. 110 to 220 vac only (one or two phase)
4. may or may not contain a gnd wire.
5. may be electrically isolated from the mains
6. cheap, diy preffered.
7. it's a power cord, I can't isolate the wire pairs.

Example in small scale; a kettle that would be plugged in permanantly to the wall anw operated by a switch on the kettle. I would like to know if it's on or off.
Large scale an oven or stove 220vac

Thanks in advance

 

[chemelec]

A Coil placed Around it or even near it will detect the AC Current Flow.
So will a Hall effect device.

You just need to Amplify the signal.

 

[mramos1]

Chemelec said it all.

I used a coil around the cord.

I will look for a schematic I had many years ago. I did this to a power strip, so when I turned on my monitor, it powered the strip, with my computer, speakers, and other toys.

I used a 3-15DC volt solid state relay and it handled 15 AMP, 110/230volts

 

[RODALCO]

I measure running hours of certain appliances e.g. TV or computer. Also for a set up as master - slave e.g. computer turned on, powerstrip is livened and printer, audio, monitor etc will be ready for use instead of having these items on standby all the time.

CCT i use and works well is very simple although a little bulky.

Old transformer 15 VA or more . Put one or two turns of ONE core of the 'sensing lead' through the laminated frame of the TF, around the other windings of the TF. Keep the mains (sensing lead) separated from the actual TF windings.

From the TF primary winding put a bridge rectifier across the terminals and a series resistor and LED for indication.
Be sure that the current through the LED stays below 20 mA with maximum load on your sensing circuit.
The smaller the TF the less likely it is to burn out the LED, although it is a lot harder to fit the extra turn around the TF.

For very light loads, less than 1 Amps the secondary of a small TF ± 30 VA may be used as a CT primary winding. connected in series with the load
The primary can be used as above to drive a LED for optical indication.

Bear in mind the electrical safety and that all mains voltages are enclosed within a well insulated enclosure.

 

[Someone Electro]

I did this once.I conected a coil to a LED bar graph driver IC.It has a internal op amp.I gave it a 1 MOhm feadback and ac cupled it whith a cap.It would detect a wire in a wall that was going to a 20W flurescent bulb.So its prety sensitive.

 

[Oznog]

It's not really possible if you don't cut the cord to spread the wires apart. The equal but opposite magnetic fields of the two wires will cancel each other out, leaving no signal to read. There's only a small, inconsistent difference from being closer to one wire than another and that may be comparable to noise emitted from other sources in the area.

 

[Hero999]

It is possible but you need to put the sensing inductor nearest to the live or neutral wire.

 

[Someone Electro]

Well it goes quite well.

If i have ben able to detect curent runing to a 20W light and that wire was inside a wall,so thats 90mA only (we have 220V) it would be able to detect 2 Amp no problem.

I put it above the light switch and when i thurned it on the bar graph went all the way to the top.When i thurned the light whith off the bar graph went to zero.

For the coil u used the prinary if a small mains transformer.I also swaped all its E shape plates to fance one way,so i can get the most output from it.