ST Plug "power" exact meaning

A ST plug using device type “SmartPower Outlet” and connected to a mobile airconditioner (the thread’s not about whether it should be lol) reports every 3-5 minutes something like “55.2w”. Sometimes it reports about 3 times a minute. I assume it’s triggered to report when the “power” data changes.

The question I am asking is, how do I use this statistic? Because as I understood wattage, it’s supposed to be power used during a time period, and usually means an actual amount of power used over a period of time. Since these reports are appearing as snapshots, how do I use them in a calculation to work out the power used by the airconditioner over a period of time?

Power (watt) does not have time. Simplistically, it is Voltage * current (AC works a bit differntly than DC). Energy is time dependent and would be expressed in watt-hours.

I see. So do the plugs not have a way to summarise the total electricity used per (whatever time period), or have I simply chosen the wrong DTH to give that to me? (I chose the one that works local you see)

I have found this equation: [number of hours’ use] x [number of days’ use] x ([capacity of appliance expressed in watt] / 1,000) = number of kWh but I don’t think that can be right as surely an aircon uses around the same as a heater when it’s running. I put the 55 in for capacity - since the plug reported that as what it’s using.

You just take the kWh and multiply by your utility rate. I have a Piston that calculates the usage and sends notifications. You can easily edit it for your likings.

Here’s another example where it’s calculated and gives you a graphical representation on your webCoRE dashboard!

So was that equation I found not right then? Substituting my values - bearing in mind I only want to know what it used for an hour while it was on -(not for now interested in the billing :slight_smile: ) I get

[1] x [1] x ([55] / 1,000) which doesn’t come to the approx 3kWH I’d have expected. Now I used actual reported rather than capacity - is that not right? I should take capacity from the details on the product rating? If it’s not right to use the reported 55W in that equation, what does it factor in?

If the power reported by the smart plug is accurate, and it reads 55W while the Air Conditioning unit is running, then this device uses 55WH of energy in one hour, or 0.055kWH in one hour.

I agree that these numbers do not seem accurate at all. That is less that an old-fashioned incandescent 60W light bulb.

In comparison, I have two Heat Pumps for my home, one per floor. The downstairs unit (smaller of the two) draws about 1640 Watts of power when running in Air Conditioning mode.

I agree with @ogiewon that 55 watts does not seem correct for an air conditioner on cooling. What type of mobile air conditioner is it? Is it possible that only the fan is running? With the fan only running 55 watts sounds reasonable, but on full cooling with the compressor running it should draw more that that. Is it blowing cold air when you are reading 55 watts?

It would be difficult to take snapshots of the power draw to calculate the actual kilowatt hours of energy used by an air conditioner over a period of time since the compressor is usually cycling on and off to maintain a temperature setpoint. The snapshots would only be accurate if the air conditioner compressor is running continuously over that period of time.


What’s the brand and model of the air Conditioner and what country are you in?

In the U.K., an A or A+ rated mobile air conditioner will usually draw about half the power of a typically sized plug in heater. They are often 550 to 850W.

On a side note, I went to go take a screenshot of how my HEM’s Tile looks, mostly Iris Smart Plugs and got this:


Read this in the IDE:

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It’s a “Challenge” from Argos (UK). 5000BTU. I have a technical information sheet in the manual. It says “Electricity consumption of single duct appliances” which is lazy - why don’t they tell me about my appliance? Anyway the value of that says 0.6 KWh. If that is true, then possibly the plug report is simply putting the decimal point in the wrong place, since the readings are between 52 and 58 watts. But on the other hand how can it be true? You can’t cool a room on that sort of power. We have a similar model - different brand, Amcor - in another room. After turning that on for about half an hour, the room drops by about 3deg c. The room with the one I am measuring doesn’t seem to drop at all while it’s on - but the air coming out of it does feel chilled. NB it’s not one of those that chills the room by blowing over a water reservoir in case you’re wondering - I would expect that to have a low energy consumption. This one is supposed to be an orthodox compressor type with a venting duct

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Please take a screenshot of your tile when the A/C is running. 52 to 58 watts to run an A/C seems way too low and if it is true, then I need to invest in that company!

You say it feels chilled but it doesn’t seem to cool the room…I wonder if the compressor is actually running. Would you have a thermometer to measure the supply air temperature of the unit in question and compare it to the similar model in the other room…with both units set at full cool? Temperature reading of the room in question would also be helpful to tell us if the air conditioner is actually doing any cooling. A typical air conditioner should have about a 8 to 11 deg C (+/-) drop across the cooling coil with the compressor running. When you take the readings, if you can close the venting duct so the room temperature will be the actual temperature of the air entering the cooling coil.

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Yeah that’s measuring the rooms via the Sensibo stated room temperature. But I am pretty sure now having tried all variations that it’s simply the reading in the ST app from the ST plug that’s wrong - and simply by a decimal place. When it says 55.2w it should really be saying 552w, and that then would agree with the stated rating of the appliance. The aircon in the room that is making the room colder is stated at around 1kw rating, which probably explains why it’s actually cooling the room! Basically without thinking about it we bought a couple of rather unimpressive air conditioners lol. I’ll remember to mentally adjust the plug’s reported wattage in future, then I’m sorted.


If you have a lamp fixture (table lamp, floor lamp, etc…) that you could plug into the Smart Outlet, with a ~60W incendescent light bulb, then you could very quickly determine if the issue is simply a decimal place type of issue.

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In the UK, that’s just called a “table lamp.” They don’t typically use “fixture“ to refer to electrical devices. A ceiling light in the UK is called a “light fitting” or “luminaire.” :wink:


Pfft not seen one of those for many a year :slight_smile:

It doesn’t have to be that. Just any device you can plug-in where you know what the probable draw should be, so you can check to see if it is just a decimal place error.

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Just tried it with my 2Kw heater - says 202w where 2020w would make more sense. Different physical plug but still smartthings with the same DTH