2023 Hackaday Prize: A Smart Powermeter That You Actually Want

[Jon] wanted to keep track of his home power use, but didn’t want to have to push his data up to some cloud service that’s just going to leave him high and dry in the future. So he went completely DIY.

This simple and sweet build is now in its third revision, and the refinements show. A first prototype was nothing more than an ESP32 with a screen and some current transformer (CT) sensors to read the current flowing in the wires in his breaker box. The next version added a PCB and a color screen, and the most recent version swapped up to eInk and a nice local power supply, all sized to fit a nice clear power box.

What’s really cute about this design is the use of standard phono headphone jacks to plug the CT sensors into, and the overall sweet combination of a local display and interactivity with [Jon]’s ESPHome-based home automation setup. This design isn’t super complicated, but it doesn’t need to be. It has one job, and it does it nicely. What more do you want?

If you’re interested in getting into ESPHome and/or home automation, check out this great ESPHome resource. It’s probably a lot easier than you think, and you can build your system out one module at a time. If you’re like us, once you get started, you’ll find it hard to stop until everything falls under your watchful eyes, if not your control.

19 thoughts on “2023 Hackaday Prize: A Smart Powermeter That You Actually Want

  1. Rarely am I inclined to be “that guy”, but “phono jacks?” c’mon. You could argue about what constitutes a “phono(graph) jack” but as handy as they are, it’s definitely never been a 1/8″/3.5mm TRS audio jack.

  2. Technically it is NOT a ‘powermeter’ since it does NOT measure the voltage, only sensing current thru a wire. You can put all the lipstick on a pig that you want, but it is still a pig.

    1. Base on the original design i saw, It measure voltage from the adaptor, the used adaptor is step down transformer, before making DC, the AC is measured there were setting to compensate transformer error. Now if this linear, idls this Class1 accuracy that is another topic, certainly it can measure voltage, phase angle between voltage and current, aka PowerFactor, using this kWH and other parameters can be compute.

      1. This design does NOT measure the input voltage. I have looked at the design software; it uses a constant of ‘230.0’ for the voltage to compute the power. There is no provision for the input voltage to even be measured in the hardware; he uses a sealed 220V to 5VDC power block. So yeah a design could be done that actually measures power, but this is not it. Sorry.

  3. You can’t deny building something like this is for the exercise, but you have to wonder: What’s the payback period? Never mind the engineering and build time: Between the capital cost of the parts and the ongoing (though small) amount of power the CT burden resistors and the device itself use, will it ever actually save more than it costs?

    1. It’s actually way less than most people assume. I did something like this, allow me to explain:

      I paid 90 dollars for a proper ‘Shelly’ wifi-enabled powermeter (measuring both current, voltage and powerfactor for all 3 phases) for my home to easily recognize the big power-draws and to no surprise it was: Dishwasher, Clothes-washer, waterheater and the electric underfloor heating in the bathroom.

      I then spent 25 dollars for 4 wifi-enabled relays and a raspberry pi with homeassistant to make it all work, while keeping me in control of my data and appliances, and i spent maybe 4 hours wiring it and setting it up.
      I’m on a hourly price-plan for my electricity, and now my dishwasher, clothes washer, and electric water-heater only turns on in the cheapest hour each day, and i make a calculation for which hours the floor-heating in the bathroom should be on (divided the day in 4, and use the cheapest hour from each, making it run 4 hours in total. This was roughly equivalent to what the thermostat did, and the floor isn’t super-hot, but it’s dry and your feet wont freeze to it during a toilet-break).
      Compared to the normally expensive hours these normally run in, as i shower when i get home from work, and start the washers while i make dinner, i use around 5kwh a day from these alone (more in winter, less in summer), and on average i save around 25c per kwh i use when it’s cheap compared to around dinnertime where i would normally use it. The 4 relays, rpi and powermeter combined use less than 10 watts idling, meaning ~0.2kwh a day = 10c a day. The raspberry pi is 4 of those watts, and it was already running, so actually less in my case.

      That makes the total payback period only 3 months, discarding the hours i spent on it, but including the powermeter which is now redundant to saving power since the relays measure current too, and as a bonus these appliances now run on almost exclusively solar and wind-power, since power is cheap when those are producing and i put less strain on the grid.

      When i set this up 8 months ago, the price-difference was regularly over 50c per kwh due to natural gas being insanely expensive, making the payback less than 2 months, but in normal times it’s not that steep.

      If i had solar cells and used the power they generated, the difference more than doubles since i would save grid-fees.

      If i had an electric car and charged it in the cheapest hours every night i would save a bit less due to the car not being able to charge during the day(This makes the highest difference in summer when solar is the biggest producer), but i would still save at least 15c per kwh = 2.7 dollars a day for my commute (90 km a day on average, 0.2kwh per km), and i would need a 3-phase relay for around 100 dollars for switching the charger on and off, but the payback for this would only be a month.

      1. Wow. I can see the incentive in that situation. Paying $0.11/kWh here, 24x7x365, and averaging $50/mo. So I’m in a completely different game where a device like this doesn’t really help matters.

        1. Yea, taxes are crazy here in Denmark…. The average price is 0.44 dollars at the moment whixh is pretty average compared to previous years when you factor inflation in, but this winter the average was 0.81… Luckily i moved in october, because my previous home was using 10.000 kwh a year due to a badly designed heatpump setup, so i would’ve hit 680 USD a month if i hadn’t… Crazy times

        2. I’m in a similar situation to you, my current use of electricity is billed at a constant rate. I’ve been running a “power meter” for about four years and other than the initial geewhiz factor, it’s not used for anything as it does not affect my use of the aforementioned power hogs. Even for those homes on tiered power plans, one learns within the first month which devices are the power hogs and therefore what time do best run them out.

          Aside from that, I use to follow another fellow’s website who used power monitoring to ascertain which appliances were failing, for example, he once identified a failing freezer because of its cycling rate.

    2. Not everything have to have a payback time. Some things are made for fun, some for building a portfolio, some for learning.

      It don’t have to save any money when building it makes someone smarter or more satisfied than before.

  4. First, this was posted on HAD a few days ago?! Also, Phono jacks?! – this is not a power meter. It’s a current meter. It cannot measure current ad it doesn’t have any clue about the actual voltage and phase shift.

  5. As its only sensing current, and does not account for the power factor it will be highly inaccurate for any reactive load such as those from switched mode power supplies. So yes it will be fine for your oven, kettle, toaster or iron but for any electronic kit such as phone or tablet charger, laptop or desktop computer or modern TV. Therefore any savings suggested by unplugging these when on standby are largely illusionary.

    1. The way something like the cheap PZEM power meters get around this is by powering themselves from the same circuit, and measuring that for voltage. It’s kind of important!

  6. If people are interested in a fully local power meter, I bought an iammeter whole house power meter a while back. I’ve had some minor issues with it but overall I’m very impressed. They have an optional cloud service but you can fully turn it off (or they even allow you to self-host it) but they also have Modbus and MQTT local APIs as well as a Home Assistant integration. The OpenEnergyMeter/Emon hardware is also a really interesting/versatile platform but availability has been a bit unreliable.

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