Checking Power Consumption of Appliances With an Energy Monitoring Adapter

Updated on November 3, 2017
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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? - 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 and freezers 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 - What is Energy Consumption?

Power 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 is likely to be an electric shower having a power rating between 5 and 10 kilowatt.

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 device in one hour, or 100 watt for ten hours or 500 watt 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.

E.g. A 2000 watt heater is turned on for 3 hours. How many kWh or units does it use and if a unit costs 13c, what is the cost of running the appliance?

  1. To convert to kW, divide 2000 by 1000 giving 2kW
  2. Multiply by the power in kW by the time in hours to calculate the kWh so 2 x 3 = 6kWh
  3. Multiply by the cost per unit. So 6 x 12c = 72c

Or you can just work the whole thing out in one stage:

So cost = 2000/1000 x 3 x 12 = 72c

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

Cost of Running an Appliance

Cost = Power in kW x Run Time in Hours x Cost per Unit

Appliances That Use the Most Power

The highest powered appliances are:

  • Electric ranges (also known as electric stoves or cookers)
  • Air conditioning
  • Kettles
  • Electric heaters
  • Microwaves
  • Hair driers
  • Vacuum cleaners

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 | Source
Voltage Display
Voltage Display | Source
Current Display
Current Display | Source
Power in Watts
Power in Watts | Source

Energy Monitoring Adapters from Amazon

P3 P4400 Kill A Watt Electricity Usage Monitor
P3 P4400 Kill A Watt Electricity Usage Monitor

This energy monitor has received a 4.4 out of 5 star rating based on 3552 reviews.

It measures and displays volts, amps, watts, frequency, kilowatt hour consumption and cost by day, week, month and year.


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.

Questions & Answers

    © 2012 Eugene Brennan


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      • Altay Gursel profile image

        Altay Gursel 2 years ago from Moscow, Russia

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