ESPHome energymeter Irms Vrms Power misunderstanding

ESPHome
1

Hey,

So I need some help understanding the Power meters.
I use a few wall plugs with metering and also a CT clamp with ESPHome.
What I have noticed is that the current and voltage will not equal the power on any of them.
One example is my Sonoff Dual R3 that reports
230V 0.29A and ~33W
But 230 * 0.29 = ~66W

Googling around I found that the power might be VA which is calculated from Vrms * Irms.
But the strange thing here atleast for me, is that the multimeter I use is a true RMS meter and should display the values as RMS and those values are the same as reported by the Dual R3.

I did my own rms calculation of the values (as if they are not RMS) from the Dual R3 and those gave me:
162.635V 0.205A and ohms law P = V * I = 162.635 * 0.205 = ~33W this matches the Dual R3 reported power.

So what im I missing here?
Is power calculated incorrectly?
is the real power ~66W or ~33W ?

2

This is indicating that the Sonoff is showing the peak voltage and current, not RMS. It however looks like it takes this into account and is calculating RMS power.

Vrms = 0.707 * Vp (same for current)

Your peak Voltage is 230V
Your peak current is 0.29A

Your RMS voltage is 163V
Your RMS current is 0.205

Your RMS power is 33W.

Be careful calling this “real” power. That has a specific meaning. See power factor:

https://www.fuseco.com.au/power-factor-correction/resources/articles/what-is-power-factor

3

Thanks, if sonoff is showing the peak voltage and current, then what is my multimeter (Brymen BM235) displaying?
As its suppose to show the RMS by default, and they match the values from the sonoff?

Here is from two other wall plugs, and these are also strange.

This one has my laptop, monitor and some usb chargers connected

[08:55:02][D][hlw8012:082]: Got power=28.1W, voltage=231.5V
[08:55:04][D][hlw8012:076]: Got power=28.1W, current=0.3A

Have a UPS and a NAS connected to below, and the UPS displays 64W load connected to it.
So the Power reported by the wall plug seems correct, but not if I use V * I which is ~91W

[08:56:09][D][hlw8012:082]: Got power=72.3W, voltage=227.3V
[08:56:13][D][hlw8012:076]: Got power=72.3W, current=0.4A

I have been adding metering plugs in the house and use the “Energy” in home assistant.
Not sure how Im suppose to read the values, what will my consumption be when I get billed etc?

Your link gave me something to continue to look for, as I guess the power reported is the real power “beer” and Vrms * Irms is the apparent power “beer and foam” which is a little higher depending on the power factor :slight_smile:

And if thats the case, I have some real bad power factor at my laptop wall plug :slight_smile: