Home Power Monitor
July 10, 2009
I completed the installation of a power monitor for my home. The web page is here. The chart comes from Google Charts; you need to wait for the chart to build over time.
It is intended primarily for relative power monitoring, not ultimate accuracy, and the energy can only be logged for short periods. It does not include power to my air conditioner (which we do not use much anyway) because that load is connected directly to the main panel, which is not adjacent to the Ethernet port I have in my garage.
There are also two temperatures reported on the web page, as described.
Credit given to Jason Winter who created this solution and published it here and here.
My implementation is slightly different from Jason’s. I utilized a different op amp (AD627), a different offset (0.5 VDC), and keept mine on a breadboard for future upgradability. I used a box with an added terminal block to convert from the CT banana plugs to lead wire for connecting to the conditioning circuit. Of course I lifted his HTML code, but modified it for my ioBridge widgets, as well as for my power factor assumption and calibration constants.
A key learning is how difficult it was to install the current transformers. There was barley enough room for them in the sub-panel. I used the Steren PUN-285 as suggested by Jason. But these CTs are really for temporary installation, and therefore are not optimized for minimal space. It was a chore to get the panel cover back on in my particular case.
Sub-panel with power monitor above
Detail of current transformers on two legs.
Detail of ioBridge (left), breadboard with two conditioning circuits, and terminal conversion box.
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