hey,
I was thinking of measuring the voltage and current consumed by any household device directly by using an Arduino.
The voltage levels are 110V/220V and am assuming to measure a max current of 10A. I know we'll need to scale down the voltage and current to the ADC's values.
How should I go about it?
You may wish to develop this yourself and if so we can advise but take a look at this.
http://openenergymonitor.org/emon/
The steps one of our products uses:
Step the AC voltage down to a much lower level, you can use a precision voltage transformer or precision resistors in a voltage divider then use an opamp buffer to scale/shift this to be compatible with a precision analog optical isolator then feed it's output to another opamp that buffers/scales to an ADC. Use math to figure out what the varying voltage should read (RMS)
Use an internal 0-5amp CT (current transformer) to smaller current (0-200ma will do) that will be converted to a voltage that will be opamp buffered and fed to the ADC.
The 0-5amp transformer will not be enough but it is enough to read the 0-50amp or 0-500amp CT that scales to 0-5amp for you. The reason for the daisy chain is to keep as much voltage/current away from the device AND you as possible.
In both of the above cases you will most likely need to calibrate both the voltage and current readings. This would mean you use an accurate voltage and current meter and measure the difference between your calculated values and real world measurement. This usually is just an offset you add or subtract from what the ADC is reading.
You would have a heavy gage wire connected in a loop on your isolation board that would go through the coil. The long wires then go to the wires on the larger coil, the larger coils is connected to mains.
"CT secondary loop"
http://www.kilowattclassroom.com/Archive/AN0008.pdf
You would want a split core for the larger CT. The smaller one would be permanent.
I grant that you can find 50A to 50ma CT's but I'm mildly paranoid about high voltage.
hey thanxs a lot for the awesome reply :)...that was indeed what i was looking for, but there's a little bit more to it.
Can i measure the pf of the device too? I've heard of zero-crossing detectors and all...but need more help on it...
You can download schematic diagram and source code from Smasma.com is for sale | HugeDomains
This device can measure 5 A current and calculation power factor. For high current use current transformers.
Not sure why you want to measure the Power Factor. Did you know you are not charged for the actual power consumed but only for the power projected onto the real axis. Therefore if you have a highly inductive load like a fluorescent tube and you take out the power actor compensating capacitor you can run it for virtually free.
well that is not really true, any device will take its share of real power apart from the reactive or apparent power depending upon the pf.
If the pf is high or closer to 1, the reactive power is close to 0, otherwise it either draws lagging or leading current depending upon the pf and we have to pay extra for it, if not compensated as you said.
So my ultimate goal is to measure the pf, and the power consumption and afterward maybe provide compensation capacitor banks.
So my ultimate goal is to measure the pf, and the power consumption and afterward maybe provide compensation capacitor banks.
Your power company might be a good resource for info relating to your project. At the residental 110/220v level I doubt you will get any reduction in your power bill, if saving $$$ is your goal.