Meter All The Phases: Three Phase Energy Meter With OpenWrt

Keeping track your overall electricity usage is a good thing, and it’s even better if you know where all the kilowatt-hours are going. [Anurag Chugh’s] house has the three phases coming from the electrical distribution box tidily organized: One for the lighting and fans, one for household appliances, and one for the hot water supply. To monitor and analyze the electrical fingerprint of his house, [Anurag] installed a 3 phase energy meter and hooked it up to the internet.

[Anurag] acquired a Selec MFM383C 3-phase meter with Modbus interface and three current transformers, one for each phase. After everything was wired up and installed in the electrical distribution panel, he hooked up an Android tablet to the meter using a USB to RS485 bridge. He started reading out the Modbus registers from the meter using the monitoring app. After verifying that the app was reading sensible values, he went on to configure an OpenWrt router to connect it up to the Internet.

While the meter also connects to his OpenWrt TL-MR3020 router through a USB to RS485 interface without problems, the whole setup doesn’t come without challenges. The latest version of OpenWrt fills up most of the internal flash memory of the router, leaving too litte space for the additional modules needed for the project. [Anurag’s] workaround for this is to compile a stripped down version of OpenWrt that allows for shifting the file system to an external USB thumb drive over the router’s serial port, which of course required opening the router and soldering in a USB to serial bridge.

With the router up and running, he wrote a compact OpenWrt package to read out the data from the energy meter through a command line interface. A cron job periodically executes a little script which polls the meter and uploads the data points to an Initial State account. There, the collected data can be further processed and graphed through an appealing web interface.

[Anurag Chugh’s] build is certainly well done, but what really stands out about this project is the detail and structure of documentation. It comprises a series of four extensive posts, where all steps are fully documented down to the lowest level, ready to be replicated and learned from by fellow makers and hackers. We’re sure you’ll enjoy the read!

Thanks to [Jamie] for the tip!

Filed under: home hacks, linux hacks

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