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Performing your home electricity consumption audit

August 12th, 2018


Everyone from us gets the electricity bills. But were you not curious to learn the usage pattern and which electric devices contribute the most to your bill? I mean not by the vendors declarations but based on the measurements. I was curious and I decided to perform my home electricity consumption audit.

There could be different ways to perform it but I chose to use something what would log the data, produce reasonably nice plots and work on mobile out of the box. Guess what can do this? Well, Sonoff Pow R2 (via eBay).

With Sonoff Pow R2 Performing your home electricity consumption audit

Just before you will proceed – whatever is presented in this post it is only my opinion. By following any of the steps might create life hazard,  you might also violate your house insurance policy or do other harmful things for yourself and/or the property itself. So, please if you are not knowledgeable and skillful enough in this field do not follow any of these steps. Whatever you do – you are doing at your own risk! 

My opinion about Sonoff devices

Sonoff produces quite cheap devices for smart-house. Pay attention to the word “cheap”, which means there are shortcuts but they are really affordable at the same time. There are plenty of extremely positive reviews on Internet but there are only few, which pay attention to the safety issues of this device.

Few of them are here:

Is Sonoff Pow HW really safe to operate with higher loads?

Let’s start from the declarations of the vendor. The Sonoff Pow R2 device (via eBay) is advertised as able to handle 16A 250V. Some guys got excited and connected e.g. immersion heaters to the device, which sounds very cool to control remotely etc. But is it really safe to operate with such currents? That is what I tried to answer to myself.

The first thing, which I did on Sonoff device, I opened it to investigate the PCB path for high currents and to check the relay model itself. Ok, it looks that a Chinese manufacturer put some effords to improve the safety of the PCB from Sonoff Pow version 1. A good sign.

Let’s have a look through issued relay different safety organisations limits. Ok, US agency declared that this relay itself can handle 10A current. But that is not what is declared by the Sonoff Pow vendor – 16A 😉

Ok, let’s move on. But what about the contacts (where you connect the wires) current capacity? I managed to find its vendor and it’s Wago and this connector model can handle … 16A!

We are coming to a last important part of high current path – the PCB itself. Well, there is no datasheet for this 🙁 but there are people complains that the PCB itself starts to heat by loading high currents.

My solution to the problem

I used 2.5mm diameter copper wire to “back” the PBC traces and to bypass the relay itself (I am interested only in measuring the load in this project). Additionally, I soldered the pieces of copper wire for other contacts (N and E) which implementation shows quite weak attitude towards safety…

Using Sonoff Pow R2 to performing your home electricity consumption audit

I read that some other users did similar tweak of soldering thick copper wire to handle higher currents.

Additionally, I got this orange socket (via eBay):

Using Sonoff Pow R2 to Perform your home electricity consumption audit


Some results of my electricity audit

I measured three different LED bulbs, some bought from eBay, while others from local shop. Their consumed power varied in the range 4.5-5.5W.

We have the bathroom heater (snake shape). It appeared that it is only …  50W. Wow. I was considering to put the timer there …

Another interesting gadget – a desktop PC with Intel i9 and GForce 960 GPU. It consumes in idle mode ~100W. If you playing with it something a bit mode intense, the consumed power is spiking up to 270W. So, if you leave not shutdown, it will be something 2.4kWh per 24h and 72kWh per month 😉

Couple years Zanussi dishwasher consumes per cycle around 1kW.

A hair dryer, which is declared 2000W (I thought the vendor is kidding), measured as 1800W.

Not too bad as for such Sonoff Pow R2 (via eBay) 😉

What else is on my mind related to performing the energy consumption audit/monitoring?

I already ordered a 30A SCT-013-030 Non-invasive AC Sensor Split Core Current Transformer (via eBay). 30 amps should be enough in most homes 😉

It would be cool to measure the power consumption and the temperature of our immersion boiler. That should help to determine the most efficient timer settings to operate it. Plus the sensor itself is inductive, so it is safer to operate or to leave unattended.