House AC best method?

I am just starting to collect parts to build a House power usage system. I find that there three common methods to convert and read the 120 vac with regular analog input.

A. Step-down transformer (9vac) to voltage splitter and full sign wave placed at + 2.5 v offset. Advantage - able to read full wave.

B. Step-down transformer to full wave bridge, cap to average, voltage splitter and 5.1 v zener to protect. advantage -- average RMS DC delivered.

C. Step-down transformer to one diode, voltage splitter. Measure + peak only. Advantage low part count. easy arithmetic to account for .2 v diode drop and 1/2 wave.

Are there other methods? What are your thoughts?

John

Lots of ideas and implementations here: http://openenergymonitor.org/

http://openenergymonitor.org/

This device used a custom interface. No thanks.

John

For some projects, yes. But you did not look very far. See this: http://openenergymonitor.org/emon/buildingblocks

Especially these: http://openenergymonitor.org/emon/buildingblocks/ct-sensors-interface http://openenergymonitor.org/emon/buildingblocks/measuring-voltage-with-an-acac-power-adapter

I don't see how measuring the voltage tells you anything about usage. So you have 120 V. so what ? How does that tell you about usage ? Where were you planning to connect your monitoring circuit ?

jremington: For some projects, yes. But you did not look very far. See this: http://openenergymonitor.org/emon/buildingblocks

Especially these: http://openenergymonitor.org/emon/buildingblocks/ct-sensors-interface http://openenergymonitor.org/emon/buildingblocks/measuring-voltage-with-an-acac-power-adapter

Yes, you are correct, good details that match my listed 'A' method. Good to know about the phase error rates. I will have to search to see if like devices are available for 120v mains. At my location I will need two. Imbalance in the split phase service is common problem here, Costa Rica.

John

raschemmel: I don't see how measuring the voltage tells you anything about usage. So you have 120 V. so what ? How does that tell you about usage ? Where were you planning to connect your monitoring circuit ?

Yes, I will also have two current transformers at the service entry point on the split phase service. That is an additional issue large enough to have a unique thread.

The bottom line of my question: Is the peek level of just the + side of the AC sufficient for this application or do I need to measure the full sign wave? I can compute the RMS from either but are there errors introduced when I move to a power computation with the current measurements?

the wonderful thing about arduinos is that you can try all three!

Let Arduino Yun Measure/Datalog DCV/ACV/DCA/ACA/R/CAP/Freq/Temperature

http://forum.arduino.cc/index.php?topic=278719.0

by select multi-purpose meter which support RMS, we could get better result.