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I am trying to identify an IC that can sit in proximity to an appliance power cord (120VAC) and simply detect if current is flowing or not. On-off output is fine; no need to actually measure the current flow.

I thought this would be a trivial exercise, but it seems not so simple. I have seen a number of examples using Arduino, or similar, but this seems like overkill for this application.

Can someone please point me in the right direction for a simple non-contact integrated circuit that outputs on/off, depending on AC current flow in a nearby conductor?

I have been looking at current sensors, like ACS712). But these seem to need current flowing through, rather than just proximity.

So then I looked at standard Hall effect sensors. I thought a unipolar version would provide an output signal proportional to average current, which should work in my application. But reading the spec sheet on US5881 seems to indicate the output depends on polarity of the field. I think this will fluctuate constantly for AC, rather than giving an average current value output.

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  • \$\begingroup\$ Have a look at the cable finder circuits. I forget what they are called - the things that look like a pen which glows when near a live mains cable. \$\endgroup\$ – Tom Carpenter May 18 '16 at 2:32
  • \$\begingroup\$ Is the power cable flat or round? By the way, the US5881 will output a series of pulses if placed near AC current, and picks up both polarities of current. With a simple interface you can still use it, but check out Tom Carpenter's advice as well. \$\endgroup\$ – Sparky256 May 18 '16 at 2:40
  • \$\begingroup\$ @TomCarpenter - don't those circuits detect voltage (irrespective of current)? \$\endgroup\$ – Roberto May 18 '16 at 3:01
  • \$\begingroup\$ @Roberto couldn't remember if they required current to be flowing or not. You may well be right. \$\endgroup\$ – Tom Carpenter May 18 '16 at 3:04
  • \$\begingroup\$ @Sparky256 - the cable is round. Are you asking because this would imply one conductor inside the other? Thanks for the clarification on the US5881- I thought the spec said output would be high or low, depending on the presence of a nearby magnetic field. I did not see anything about pulse output. Maybe I just need to research that chip more carefully. \$\endgroup\$ – Roberto May 18 '16 at 3:04
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I am trying to identify an IC that can sit in proximity to an appliance power cord (120VAC) and simply detect if current is flowing or not

Your whole requirement is "hit" by the problem that any current flowing into the load on one wire is also flowing back from the load on the other wire. These two identical currents (passing through identical wires) cause magnetic fields that cancel each other at quite small distances from the load's power cord.

So, the above method is largely unsuitable and unpredictable.

What people actually do is separate live and neutral feeds and measure the magnetic field produced by only one of these wires. Current transformers or hall effect sensors are used. However, from the sound of it this is not an option to you so good luck in finding a magical method.

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  • \$\begingroup\$ thank you for your helpful reply. Do you happen to have an example of a suitable Hall effect sensor might be suitable? I tried with the US5881, but it was not sensitive enough for household current. electronics.stackexchange.com/q/235298/58362 \$\endgroup\$ – Roberto May 20 '16 at 4:39
  • \$\begingroup\$ If you are still going down the path of NOT splitting the appliance cable then I can't recommend anything because there is a basic problem of alignment and misalignment causing flakey results. \$\endgroup\$ – Andy aka May 20 '16 at 8:26
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Devices do exist for detecting AC current (rather than just AC voltage).

For example

Extech DVA30

  • Non-Contact AC Current detection from 200mA to 1000A
  • Current sensor detects current flow through shielded wires, conduit, and metal circuit breaker/junction boxes

I have one of these and it can distinguish between current and no-current in an appliance cord that contains earth/ground, "neutral" and "live/hot/line" conductors. You often have to be careful about positioning the sensor.

I don't know what sort of sensor it uses though. I'm not willing to destructively teardown mine to find out. :-)

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