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.

energymeter_routerWhile 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!

36 thoughts on “Meter All The Phases: Three Phase Energy Meter With OpenWrt

    1. Yes quite critical at the transformer, but quite irrelevant for the tiny load that is a residential house / apartment. Remember a typical street will be wired such that single phases feed alternating houses. All that is needed is for one neighbour to invite the other two over to watch the football and you’ll have an imbalance an order of magnitude higher than this guy’s switchboard.

    1. The blog post shows an image of a distribution panel with 3 different phases clearly marked, red, yellow and blue. So I would say it is a true 3-phase installation. No idea why you’d need it in a domestic setting however.

        1. When my parents moved to Switzerland, I was confused when I saw the washingmachine and dryer being plugged into those funny 3-phase SEV 1011 T15 and T25 sockets. Here in Germany washingmachines and dryers are run from normal 16A schukos.

          When there are 3-phase devices in a houshold in Germany, they don’t use wall sockets. They are wired directly to the wall. 3-phase outlets are only used for “heavy” machines like welders.

        1. Yeah, before Inverters/VFD’s became common, running multi horsepower aircon motors from a single phase was tough – shaded pole / capacitor split motors were quite inefficient and had bad starting torque. Induction motors were vastly better but required 3 phase.

          Modern VFD’s rectify all incoming phases (be that 1 or 3) to a DC bus, the recreate three output phases with an appropriate frequency / voltage relationship. They are highly efficient and let you run an induction motor from a single phase supply quite easily.

    1. he says its split as water heaters / kitchen appliances and AC / lighting and fans
      Pretty poor balance but in the highly unlikely event of a single phase interruption you would lose either all of your hot water or all of your lights or all of your ability to cook dinner.
      Same reason if you clump circuits onto a residual current/leakage breaker you don’t put lights and sockets on the same room together so you don’t get left in the dark

      1. I lived in a apartment building once. One time i was testing a computer PSU in the bedroom and i did not notice a dog had chewed the cord, so i plugged it in. It burned the fuse from somewhere in the electrical room, but my apartment fuses were ok. The whole phase was off. It was a weekend and the repair dude did not come until monday.

        Thankfully it was not the phase where my fridge was connected to. Some other stuff was off, don’t remember if the bedroom lights went off, but atleast the tv in the livingroom worked. Can’t remember what other stuff was on that same phase, but something else must’ve been, Obviously nothing i couldn’t survive the weekend without.

  1. Where in the world is this?

    In the UK you would never see any point in a building where you can touch any two phases with either hand so a light switch on one phase would never be within 6ft (arms span) of a socket or switch on another phase. This is why light switches on stairwells in blocks of flats are never near the door to the flat, always an arm span away.

    1. A post about electrical mains is always an opportunity for some Brit or Euro to talk about how much better they are. Good to see their sense of superiority did not die out when the colonial era ended.

      1. I never considered it to be better in any way, in fact it is a complete pain in the ass sometimes.

        Your inferiority complex is bordering on needing medical attention. I suggest you go and see your doctor wherever you are, if you have them where you live.

    2. While that may have been true in the past, it hasn’t been so for decades. It’s possible to see multiple phases in one bank of lightswitches for example (usually indicated with a 400V warning label, but not always).

    3. What exactly is the point in installing different phases so far apart (i’m really curios)?
      Are the switches made from metal? If so they should be grounded to earth and a <=30mA RCD will take care of any faults.
      I can't think of any other plausible reason.

      If someone left the power on while working on the switches and sockets and touches two different phases simultaneously darwinian laws state he/she should be removed from the gene pool anyway.

      1. Given the age of many buildings in the UK, and the age of the wiring (My old school still uses the lighting installed in the late 1800’s) it is a sensible practice when adding to an existing system. It also takes into account earth faults, which are scarily common…

      2. Light switches are probably not a big risk, but regular power outlets are – especially somewhere like a kitchen or laundry where you have metal appliances.

        It takes someone doing stupid with the wiring but it’s still a genuine risk. A single miswired plug is enough to get mains potential the exposed metal on two appliances.

  2. Hi guys, here are the answers to your questions:
    I live in Pune, India.
    My apartment building has 12 floors with 4 flats on each floor. Of these, on each floor, two are supplied with 3 phase connections. The other 2 flats are with single phase connections.

    The technician who undertook the wiring made sure that the building as a whole was balanced. So if my domestic appliances were connected to red phase, the flat above mine has its domestic appliances connected to yellow, and the one above that has its connected to blue. Same goes for kitchen appliances and water heater. Not the ideal solution but it works.

    1. That’s quite a strange setup, but the balance is a non-issue. Suppose your neighbour invites you and the other neighbour over to watch the cricket, the electrical system isn’t going to suddenly break down.

  3. To clarify to N. Americans: continental Europeans mostly do have 3 phase power in their homes. Single phase is used for all purposes except stoves, large motors, and similar. To clarify to Europeans: N. Americans mostly have only single phase in their homes, that is 240 V center-tapped pole-mounted transformer, to provide both 120 V (low power use) and 240 V (stoves etc).

      1. 230 :)
        UK differs from most of mainland Europe in that it is not common to have three phases. It is an option, my house has it for example but I only know of a few others as it is 3 times the standing charge so works out damned expensive. I think that the supply to a typical UK house if probably fused higher than any other domestic supply in the world at 100 amps 230 volts. It makes a big bang when you do it wrong. :)

          1. The tolerances are changng so that eventually they will have to adjust to 230, right now they haven’t changed anything and most houses are 240 and that is within the current tolerance.

            My house is usually around 253 which is well outside but who am I to worry, free power is a good thing. :)

          2. @john do you think your mains provider count only the current?
            Here in germany they count power…
            But for private houses they don’t take the reactive power into account. You could build a lot of small capacitor power supplys…

  4. I wonder if this is the case in Japan. 50 and 60 cycle is enough, made worse by the nuclear power situation. Started in the 1920’s by German and American interests at each end of the main island.

    1. Japan confused me when I was working there, they seem to be geographically split between 100, 105, 110 and 240. I think that makes it the country with the most possibilities of supply,

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