I am trying to find ways to capture sensor output from devices that have no connectivity at all. One way is to monitor the power draw and deduce its state based on how many watts it takes to do some specific action. I have one such device that idles at 0.6W and is nominally “in-use” at 0.8W. I can use this in HA if I had a power monitoring plug that is accurate under 1W. Do they exist?
I’ve tried three such smart plugs.
The Emporia Smart Plug came the closest because it absolutely does detect loads under 1W! Unfortunately, it only shows that level of accuracy to its own app. The HA integration is cloud based and it averages the results over a minute. That’s not useful at all.
The Third Reality Zigbee Smart Plug (Gen 2) is strictly local and so pushes its updates in real-time. It can’t detect loads under 1W, though, so there’s no way to detect a 0.6W to 0.8W difference.
The Sonoff S31 Smart Plug (with Tasmota) is also strictly local and pushes its updates in real-time. It’s even worse than the Third Reality for low power accuracy, though – I don’t believe it will show anything less than 10W in HA. Its Wi-Fi web page is slightly more accurate than that, but still not less than 1W.
So, has anybody used a smart plug with local push that can detect a sub-1W load?
I use Shelly 1PM 9though no plug, but module) and it seems to record power consumption below 1W:
As you can see my washing machine in standby mode is consuming something between 0.3 and 0.4W. Not sure if this would give you enough accuracy to distinguish between 0.6 and 0.8W. Perhaps setting proper trigger level or using some averaging on top of actual readings could help to eliminate potential variations in reading.
Also with Shelly Plug S I can observe similar accuracy of readings for idle devices (coffee machine, electric cattle), though these devices seems to have more variation (±0.2W).
Oh, that’s very promising! I happen to have a pair of Shelly PM Mini Gen3s but it never occurred to me to try those with the low wattage items since I got them for their high wattage capability (one of the very few that can handle more than 15A!). I’ll give that a try and if it still skews high, will get a 1PM.
This device is based on a CSE7766 which should be quite accurate compared to other power measurement chips widely available on other devices.
To be sure your mileage isn’t a limitation from Tasmota I highly suggest to throw some esphome on your plug
Additional I would set the throttle_average on the cse7766 platform to something like 1 or 0.5s (or even less) to get most accurate readings from your plug
