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Measuring AC Current

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StudentSA

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Good Day.

My objective is to build a single phase AC power data logger that can be used to measure power consumption from wall plugs in your typical home ( 240V AC in SA )

As a basis I will require some sort of AC Current measurement and for this I want to know if its possible to use a current transformer like RS Current Transformer for AC?

In essence I am looking for a cheap way to measure AC current and thus Power.

In terms of accuracy of measurements I was thinking as long as it falls in the +-10% margin i'll be happy.

Thanks in advance,
StudentSA
 
Sorry to be pedantic but I dont think that device is any good for you, the minimum current is 5a looking at the listing, most wall warts take way under an amp.
You might be able to get a ct with a lower current range, or as long as you take saftey into account you might want to make something that looks at the current directly using a shunt, you'll probably need to measure voltage anyways so your circuit will need connecting to the supply.
 
Google Killawatt circuit and have a look at the schematics.

If you're not confident with AC mains though, be very very cautious. Then be even more cautious !
 
The main problem with measuring mains current is that you don't know whether you are looking at a mobile phone charger (2W) or a kettle (3000W). It is difficult to make devices accurate to 10% of 2W while capable of measuring or even surviving 3000W.

A current transformer like the one from RS would be a good start. It is rated at 5A nominal, 60 A max, so I would start with 4 turns on the primary, so that it wouldn't exceed the maximum current when the load is at the 15A max for the plugs in South Africa. That will give you 4 times the input and output current, so the nominal primary current would be 1.25 A. At .125 A, so 30W, with 4 turns, the output is quoted as being 4% below the nominal, so I would guess that you could go down to 5W or so and stay within 10% accuracy.
 
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