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Checking Power Consumption of Appliances With an Energy Monitoring Adapter

Eugene is a qualified control/instrumentation engineer Bsc (Eng) and has worked as a developer of electronics & software for SCADA systems.

How to Measure Power

With the cost of electricity on the increase, an energy monitoring adapter is a useful device which can measure and track the energy consumption of your home appliances. Costing about $15, the adapter can be plugged into a standard wall socket and displays comprehensive information about the appliance connected to it, including the energy usage and price of electricity used, aiding the analysis of energy use in the home.


How Do I Use It?

The adapter has prongs just like a normal plug. You just plug it into a standard wall socket and then plug the appliance into the adapter. The adapter has a display which indicates energy use.

What Does it Do, and What Can it Measure?

An energy monitoring adapter provides information about the connected appliance on an LCD display. Typically the information displayed would be:

  • Voltage
  • Current drawn by the appliance
  • Power consumption of the appliance in watts
  • Length of time the appliance has been running for and actually drawing power: This is useful for monitoring fridges, freezers and air conditioners which are switched on and off regularly by a thermostat
  • Energy consumption in kilowatt-hours or kWh
  • Cost of running the appliance: The cost per kWh is entered into the device during initial setup and the adapter multiplies this by the consumption in kWh and displays the cost in dollars and cents.

What is a Kilowatt and What Is Power Consumption?

Power consumption is the rate of energy use over time and the unit of measurement is the watt. E.g a 100-watt bulb uses energy at the rate of 100 watts.

A kilowatt is 1000 watts. This is the power typically used by an old fashioned one bar radiant electric fire. A kettle is rated at about 2 or 3 kilowatts. The highest power device in a home is likely to be an electric shower, having a power rating between 5 and 10 kilowatts.

How to Work Out Energy Consumption and Cost of Running an Appliance

A kWh, kilowatt hour or electrical unit is a measurement of energy consumption. It is the energy used by a 1000 watt or 1-kilowatt appliance in one hour, or 100 watts for ten hours or 500 watts for 2 hours, etc. To work out the kWh usage, you multiply the power of the device in kilowatt by the run time in hours.


A 2000 watt heater is turned on for 3 hours. How many kWh or units does it use and if a unit costs 30c, what is the cost of running the appliance?

  1. To convert to kW, divide 2000 by 1000 giving 2 kW
  2. Multiply the power in kW by the time in hours to calculate the kWh so 2 x 3 = 6 kWh
  3. Multiply by the cost per unit. So 6 x 30 c = $1.80

Or you can just work the whole thing out in together:

So cost = 2000/1000 x 3 x 30 = $1.80

(This article is published on a US website and I use cents, but just replace the cost per unit using your own currency)

For more information about the power rating and energy consumption of common household appliances, take a look at this article:
What is the Cost of Running Appliances?
This article shows you how to convert between volts, watts, amps, and kWh:
Volts, Watts, Amps, Kilowatt Hours, What Does it All Mean? - The Basics of Electricity

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Read More From Dengarden

Appliances That Use the Most Power

The highest powered appliances are:

  • Electric showers
  • Electric ranges (also known as electric stoves or cookers)
  • Air conditioning
  • Kettles
  • Electric heaters
  • Immersion elements in hot water tanks
  • Microwaves
  • Hair driers
  • Vacuum cleaners
  • Clothes driers

Some of the above appliances although high powered are only used for short periods of time however and so the total energy usage over say a month is low. For instance a hair drier would only be used perhaps for 5 to 10 minutes a day and a kettle several times a day, taking a few minutes to boil. Remember cost = time x power of appliance so a low powered appliance such as a freezer running 24/7 can use as much energy as a kettle over a period of a month

This particular adapter has a UK socket and plug. However models are available with other socket styles

This particular adapter has a UK socket and plug. However models are available with other socket styles

Voltage Display

Voltage Display

Current Display

Current Display

Power in Watts

Power in Watts

Tips for Saving Electricity

  • Use thermostats to control electric space heating.
  • Only boil the water you need in a kettle. It only needs to cover the element.
  • Use low energy LED lighting indoors and LED or sodium lighting outdoors.
  • Unplug audio video equipment/TVs when not in use. Standby power use can be up to 30% of fully on power.
  • If a hot water tank has an electrical heating element, use a timer to set when it is on and off.
  • Dry clothes outdoors if weather permits. Clothes driers are high powered appliances.

Detecting Faulty Appliances: Fridges and Freezers

An energy monitoring adapter comes in useful for identifying faulty appliances. For instance, if the thermostat fails on your fridge or freezer, the compressor will run continuously, putting up your electricity bill. Another scenario is that the insulation becomes waterlogged. Once this happens, the insulation is effectively useless. Again the freezer will run non-stop. The only thing you may notice is excessive frost and ice build up. You can use an adapter to check how many hours a day the freezer is running and if it is staying on too long even in cold weather, this may indicate a failed thermostat. In general, a fridge or freezer should have a duty cycle (the percentage of time it is powered up) of 25 to 50 %, depending on temperature.

With oil and gas prices rising by the day in Europe, this article might be of interest. It gives some ideas on how you can reduce your energy by making changes around the home:

Over 10 Easy Ways to Reduce Your Electricity and Gas Bills

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2012 Eugene Brennan


Altay Gursel from Moscow, Russia on December 02, 2015:

It is a very cool gadget, thank you for sharing with us.

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