Measuring power wih ACS712 hall effect sensor

Hi guys,

I am trying to measure power using the ACS712 hall effect sensor. From what I have read online I would have to use a voltage divider to make voltage measurements and then measure the power. The circuit is something like http://openenergymonitor.org/emon/buildingblocks/measuring-voltage-with-an-acac-power-adapter. But why is this voltage actually needed? Dont all household appliances run at 230v/110v? Is the voltage measurement really necessary? If so what are some of the good ways to isolate this in a cheap way? Is it optocouplers or tranformers?

Second, is there a need to interface the ACS712 with an energy metering IC? Will this make it simpler or harder for the project? Could you please give me some ideas?

In order to measure true rms active power for reactive or non linear loads you have to divide each period into time segments and multiply voltage and current for each time and average these results. Only on pure resistive loads you can calculate power by multiplying the rms values och voltage and current

The need of measuring the voltage will depend on the accuracy that you need. If just a rough stimation is needed, then assume the standard voltage in your area . jma

Okay. DO I need to use a separate energy metering IC ?