Current sensing?

A current transformer is one common way of doing this. Split core units are available that do not require the moving the wire being monitored.

Dan

See

for an example of current transformer to do what you want.

Dan

I am aware you said that you would rather not use shunts, but it would cost you very little money and effort to try out these current sensors. Just a thought.

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Is this for permanent installation or just a one-off have a look see if any current being consumed ?

If the former then hall effect sensors work real well, if the latter then borrow a clamp meter, you can buy a cheap one for around $60 or get an add on one for a normal DMM for around $25 or so...

btw: What sort of pump ?

Because if induction motor then current consumption wont guarantee the rotor is turning, so although you might see something then its not a given its actually spinning.

If it was me, I'd use a current clamp with a reasonable frequency response and interface these to a CRO, will see some nice spikies if its an induction motor and the rotor is actually turning.

Do I take it these are submerged bore pumps and some distance below ground and you cant hear them running and there is no water flow because you are investigating if the bore has dried out ?

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This is for a rural property where there is (fortunately) broadband access via a wireless link to a kind neighbour on the other side of the valley. Because the property is often unoccupied for long periods, and there are a number of irrigation and water reticulation systems that operate autonomously, I'm looking to implement some kind of monitoring system to log pump operation. I'll be using a 1-wire bus as the wireless router can be easily modified to support this (it runs linux and a bunch of geeks have implemented many mods, including 1-Wire libraries). There'll also be a

1-wire weather station. The router will transfer its data to another host at our main property. 3 of the pumps are ordinary induction motor-equipped pressure pumps, and while the idea of sensing power consumption would be nice, doing it properly would involve sensing voltage as well, and doing power factor calculations. Realistically, just logging when the pumps are operating, and being able to determine when a pump has been going longer than it should would be enough (for example, on one occasion a switch failure meant a pump ran for 3 days and flooded the property downhill). Sensing a locked rotor would be kind of handy, but not vital - its failure would most likely show up in other ways (I hope...).

The 4th pump is a borehole pump at 114m underground. This pump uses a permanent magnet motor and some kind of inverter setup - it does a 2-second soft-start drawing only 10% over the operating current. Interestingly, the specs quote a power factor of 1, but I imagine the voltage/current curve would be quite complex. Sometime I should drag a CRO out and have a look.

I remember seeing an article about using hall-effect sensors - SC maybe? I'll have a hunt around. - thanks.

Actually they look like a neat solution - I'll check it out. Thanks John.

Current sense relay ?

The better ones have under and over current sensing which can be used to indicate a fault with the motor. I've seen them used for A/C control boards for monitoring air-con motors. Much more reliable than an air-pressure switch.