The Open Energy project collects typical data from devices, so that you can better know what to expect when you are hacking away. This tutorial will provide you with an overview of how common electric devices in the home works as well as the components that they contain.
After reading the general overview you can also check out these more detailed descriptions of how specific devices use energy:
A brief History of electrical appliances
The turn of the century many cities had started to get electricity. To start with people mostly used it for lighting. Because of this power companies like AEG struggled with the problem that the power plats was standing still during the days when no light was needed and didn't earn them any money.
To help solve their problem they hired a guy called Peter Behrens. Peter immediately came up with the idea that if we can get housewives to use electricity during the day we could also start selling electricity when it was light outside. To do this he created kitchen appliances that was running in electricity.
To get as many as possible to use these new kitchen appliances he got the idea to change the handle or surface of the appliance while the internal parts stayed the same. And just like that voila!! industrial design was born.
How do they work
If we take an electric kettle the way they work is that there is a metall coil which the electricity is feed through. The friktion of the electric flow heats the coil and the coil heats the water. This is basically the same way as incandescent light bulbs work. Only in the later case the while gets much hotter. So hot that the wire goes from glowing inte emitting a bright light.
Another type of electrical appliance found in our home are vacuum cleaners, fans or electric hand mixers. These devices contains electric engines designed to create movements. The the electric engine electricity is used create magnetic fields that will move magnets connected to some mechanical part.
The third category of device are electronics in this area we find things like LED light, TV:s and all other forms of technical gadgets in our homes. Most digital devices today are powered by inverters that converts the 110-230V AC to some lower direct current.
As the last category of devices we have the combined ones. That is for example the your dishwasher or your refrigerator. These devices combines both heating coils, electric engines and electronics.
Electricity metering as a sensor
So what can we expect when collecting data from a smart plug connected to some sort of electric appliance. The answer of course depends on which kind of device. When it comes to heating coils or incandescent light the power consumption is usually quite strait forward. As you turn the switch on you kettle or lamp will start consuming a power value quite close to the rated value on the device (e.i. a 60W bulb will consume about 60W and a 2000W kettle about 2000W).
An electrical engine as well as electronics on the other hand will consume power i relation to the load. In other words an electrical engine lifting 10kilos will use more electricity than the same engine lifting 5kilos.
As for combined devices such as the washing machine they will typically run on a program which activates the different components in the machine based on a schedule and sensor input.
With electrical appliances we can of course measure their consumption and By looking for specific pattern of consumption we can detect which machine we are currently measuring. And by looking at small changes in those patterns we can detect things about how the device is being used if its working properly and so on. Here are a few examples:
- Detecting temperature of a coil
- Detecting ageing and malfunctioning of a heating coil
- Detecting energy used for heating.
1. Detecting the temperature of a coil
The resistance of a heating coil is related to its temperature. Because of this the power consumption will be slightly higher when the power is turned on and then decrease a few percent as the coil becomes hot. The same phenomena also occurs in incandescent lamps however in lamps it will be really fast as the wire inside the lamp heats up to it's full temperature in less then half of a second. In a kettle the decrease of power usage can potentially be exploited to get an indication of how much the water has been heated. The better heat conductivity between water and coil is the better this will work.
2. Detecting ageing and malfunctioning of a heating coil
As a heating coil ages it's resistance will increase. As a result the its power use will decrease. If monitoring a device over time a slow decrease of power use in the heating cycles can therefore be used as a measurement of ageing. If the coil breaks they will typically stop conducting electricity altogether and the power usage will drop to zero. A drop in power usage, fluctuating power usage or an abnormally large decrease in the power usage as the coil heats up can be a sign of a bad connection to the heating coil. Bad connections are dangerous as the connection itself risk becoming hot enough to cause a fire in the machine and the surrounding plastic insulation.
3. Detecting energy used for heating
Typically in a kettle or a washing machine or dish washer there is a termostat that will switch off the coil once a certain temperature is reached. The heating time depends on several factors like:
- What the desired temperature is.
- What the starting temperature in water we are heating was when we started.
- The amount of water to be heated.
- Insulation of the machine.
Even in combined appliances like the washing machine the heating coil stands out as its both a big power consumer and quite constant in its power use (with the exception of the small change discussed in nr 1) and can therefore easily be detected.
The about of energy used for heating can be used to determine:
- Approximately how much water that was loaded into a kettle given that the kettle doesn't have multiple temperature settings.
- What temperature setting you are using on your washing machine (for example 40°C, 60°C or 100°C).