cvrider

I have attached a schematic of a circuit which I want to build to monitor a 120V AC household (US) circuit. In the top section of the circuit I am using a voltage divider to monitor the voltage in the 120VAC circuit, and in the lower section of the circuit I am using a shunt resistor to measure the current in the 120VAC circuit.

I am somewhat nervous about directly tapping into a 120VAC circuit. Can someone review this to see if it looks good enough to try without frying my equipment and myself.

Also, for resistors and caps (especially the shunt), do I need to buy a certain type of resistor or cap to handle the larger 120VAC load. I am used to working on 5V DC circuits and similar and I am not sure if there is a certain type or Wattage that each component needs to handle the 120V circuit.

Thanks.

Attached Files

circuit.pdf (15.4 KB, 29 views)

eblc1388

You should be nervous. The circuit is no where safe as you have placed a shunt in the Live wire and tapping voltage off it.

What actually do you want to monitor? The value of voltage and current or just their presence? There are safer ways to do all that.

Also what is the equipment? Is it a microcontroler or just meters?

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L.Chung

aussiepoof

AC current is best measured using a current transformer which provides galvanic isolation - aka not tapping into the AC so it doesn't bite you :-) You can google "current transformer" for a more accurate description :-)

A transformer could also be used for measuring voltage, though no doubt others on here have better ideas.

P.

ericgibbs

hi,
In the UK, you can buy for a few pounds, a ready made adaptor, it plugs into the wall socket and you plug the piece of equipment you want to measure into the adaptor.

A small LCD on the adaptor displays the power consumption and other information.

Is this the application you have in mind.?

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Eric
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cvrider

Eric,

You are correct that I want an application that measures power. The previous circuit that I showed you will be connected to a CS5466.

http://www.cirrus.com/en/pubs/proDat.../CS5466_F1.pdf

I was given the current sense and voltage divider circuits. I understand you can also use a transformer, but I was having a hard time understanding how to integrate the transformers into the circuit with the CS5466.

Hero999

You can also measure voltage with a standard mains transformer, just measure the divide the secondary voltage by the primary voltage and you'll get the exacy dividing ration. Don't load the transformer too much or it will give an unreliable reading.

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