Current sensing?

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I need to sense the operation of a couple of pumps in the 1 to 2kW range.
Measuring the actual current would be nice, but just knowing they're
operating would be enough. I'd rather not use shunts - I think there's
enough current to be able to see what's going on by attaching something
around the active to each pump - anyone have any ideas?




Re: Current sensing?



Poxy wrote:
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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


Re: Current sensing?


current clamp?
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Re: Current sensing?



Joe G (Home) wrote:
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See http://www.split-core.com/ for an example of current transformer to
do what you want.

Dan


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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.

http://www.allegromicro.com/sf/0750 /


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Re: Current sensing?



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





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says...
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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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Mike
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Re: Current sensing?



snipped-for-privacy@poxymail.com says...
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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.









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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.

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