5mo ago

Questions about Zigbee, Wifi and Smart-Plug measurement accuracy

I want to dip my toes into the smart home world and decided that I want to use homeassistant and primarily use devices based on zigbee, as I do not want to overload my wifi with a bunch of devices.

Smart plugs seem to be most interesting to me as I would like to have accurate power measurements for my homelab and applicances. The keyword is accurate here. There seems to be some science showing that the accuracy of smart plugs can vary a lot. I have read that devices that are flashed with the tasmota firmware can actually be calibrated. Unfortunately this firmware is only available for wifi devices.

So my questions are:

Are there zigbee smartplugs that are known to be very accurate or can be calibrated to be very accurated?
Is preferring zigbee over wifi actually a good Idea? I mean both use 2.4 GHz, which is known to be crowded. When will wifi smart home devices become a problem?
Is a calibrated tasmota smart plug more accurated than a typical zigbee plug?
Is this inaccuracy reported in the paper even relevant for non-scientific use?

12 comments

How much precision would you need? Why? How would you calibrate one? Do you have the pliers/calipers used by electricians?

Personally I would avoid ZigBee and Z-Wave for devices that report a lot of data. They tend to crowd the network pretty fast.
- Zwave uses a different spectrum than zigbee and wifi though, so as far as wireless communication, it's probably the most reliable.
  Wired is mostly impractical for outlets.
  
  Doesn't change that the bandwidth for Z-Wave is tiny, and it's a mesh, both of which means it's not well suited for large amounts of data, like high throughput sensors (of which power reporting is one example). I have four dozen wifi devices and really don't have any issues, I think it mostly gets a bad rep from people who a) use 2.4Ghz for other devices (I put only IoT on 2.4, everything else is on 5Ghz) b) use shitty home gamer access points instead of something decent like Ubiquity/Microtome/TP-Link etc.

Some Zigbee smart plugs and sockets have configurable calibration settings. I have some SmartThings smart plugs that have calibration settings, and I think the new IKEA smart plugs with power monitoring have calibration settings too.
There are some resellers providing generic Wi-Fi smart plugs pre flashed with Tasmota and calibrated correctly. Not sure where you are located but in the UK I can recommend Local Bytes.
I've also seen people recommend Shelly devices for power monitoring for accuracy. The Powercalc integration developer used to recommend Shelly devices for measuring power use of new devices to create Powercalc profiles.
I wouldn't expect too much from accuracy from any of these smart devices though. They are intended for general consumer use to provide general ideas about energy use - they are not scientific instruments and probably shouldn't be treated as such.
If you are looking to monitor homelab devices specifically perhaps you should look at a more professional/enterprise PDU instead.
Remember that to properly calibrate any of these devices you will also need an accurate reference device to calibrate against.

I've got z-wave monitoring plugs from both minoston and zooz, and they give the same readings as Kil-A-Watt.
It looks like your source is focused on loads that switch on and off frequently, which is probably important for laboratory, but not really for home. The reporting interval for my plugs ranges from maybe 3s to 30s, and I can imagine that there's internal lag between measuring and reporting, but it's not relevant to anything I can imagine using the data for.

Zigbee > WiFi
Zigbee is a mesh, it's more reliable, it's low power so it allows for battery powered devices
Z-wave
Perhaps even more reliable than Zigbee due to using a different spectrum
Home Assistant can run Zigbee and Z-wave radios simultaneously. I have two. Then you can pick devices from a wider range of vendors and models. When considering smart plugs, keep in mind that most have relays rated for non-inductive loads. Motors are generally inductive loads. I'm not sure if computer power supplies with their big capacitors would cause similar problems or not. If you want to be able to plug anything without thinking, make sure the plug you buy says its rating is valid for inductive loads. I have some units from Zooz which qualify. My IKEA ones definitely do not. Philips don't either but they've survived switching some ductwork fans for a few years.

My Z-wave switches and smart plugs are reasonably accurate for a common house use, but I wouldn't say that they are 'very accurate'. I haven't done any measurements, but if in example I plug in an appliance which has 200W on label I get roughly that number from the system. But obviously I don't have any way to tell if the smart plug shows wrong value or if the label on the device is incorrect. And with things like LED bulbs the current varies anyways with temperature plus I don't know if the things take actual line voltage into account which varies a bit as well.
For my use case they're accurate enough, but if you need 'electroncis lab accurate' results I doubt that any of the smart plugs can provide that.

Despite fairly congested 2.4ghz wifi in my area with 18 networks detected by my phone, all Zigbee and Tasmota wifi devices on my network are nearly 100% reliable. In my experience Zooz Z-wave devices have been less so and occasionally are unresponsive. Other Z-wave devices have been much better.
The Tasmota plugs and lights in my network generate very little network traffic. Power monitoring plugs will generate more, but with 1 second update intervals that traffic should still be minimal.
- Damn, that's crazy to hear! Zooz stuff has been the bedrock upon which I've built all my automation. Like, I have dozens of ZEN04 LR plugs all over my house. What specific Zooz stuff has been unreliable for you? I've only used the ZEN04 LR, ZEN14 LR, and ZEN15 LR plugs so maybe it's just not anything I've ever touched.
  
  I have two Zen 30 switches and since I wrote that comment a week ago both have died. Zooz is blaming the failures on an installation error after 18 months of use! Instead static discharge is the logical cause and since it's a fact of life in my home, if Zooz won't replace the Zen 30's I'll move away from their devices and will install Shelly wifi relays and Minoton wireless controllers instead.
  The Zen 30 switches have mostly worked until now, but occasionally they haven't responded to Home Assistant for a minute or two - really frustrating when standing in the dark waiting for the lights to come on. Leviton dimmer plugs and Minoton wireless controllers connected to the same Zooz Z-Wave stick have been flawless, as have all my Tasmota wifi and Zigbee devices.

12 comments