How to measure energy usage and power consumption of your electronic device?

Posted by admin 12/04/2017 0 Comment(s)

How much actual electrical power is your electronic device using?


Are you looking for ways  to measure how much electrical power your device (such as Computer, PC, Mac, Fridge, TV, Monitor, etc.) is using? If yes, than read on. There could be plenty of reason trying to figure out how much energy your household appliances and gadgets are drawing. Maybe you want to save on the electricity bill? Minimise carbon emissions? Or perhaps size a Uninterruptible Power Supply (UPS) to protect you electronic devices and provide some battery backup during a blackout?

So in this article we’re going to investigate different ways you can measure your energy usage. These methods vary based on simplicity, accuracy and accessibility to particular instruments and tools. Our aim is to give you multiple options and help build a clear understanding on how it works.


Introduction to Electric Power and understanding how it works


Electrical power is measured in units called Watts. Put it simply, Voltage and Current give you electrical power. The Voltage is a kind of electrical force that makes electricity move through a wire and we measure it in volts. The bigger the voltage, the more current will tend to flow. Voltage does not, itself, go anywhere: it's quite wrong to talk about voltage "flowing through" things. What moves through the wire in a circuit is electrical current: a steady flow of electrons, measured in amperes (or Amps)

The electric power is equal to the Voltage × Current (in other words: Watts = Volts × Amps). So if you have a 100-watt (100 W) light and you know your electricity supply is rated as 230 volts (typical household voltage in the Australia), the current flowing must be 100/230 = 0.4 Amps.

Confusion between electrical Power and Energy

Power is a measurement of how much energy you're using each second. To find out the total amount of energy an electric appliance uses, you have to multiply the power it uses per second by the total number of seconds you use it for. The result you get is measured in units of power × time, often converted into a standard unit called the kilowatt hour (kWh). If you used an electric toaster rated at 1000 watts (1 kilowatt) for a whole hour, you'd use 1 kilowatt hour of energy; you'd use the same amount of energy burning a 2000 watt toaster for 0.5 hours or a 100-watt lamp for 10 hours. See how it works?

Household electricity meters show the total number of kilowatt hours of electricity you've used. 1 kilowatt hour is equal to 3.6 million joules (J) of energy (or 3.6 megajoules if you prefer).


Estimating Power Rating Using  The Manufacturer’s Label or Rating Plate (Name Plate)


Nowadays, most of the electrical equipment comes with a rating plate which identifies the amount of Electrical Power (Watts) it consumes. So the ‘name plate’ or a ‘rating plate’ should be your first point of reference when establishing power requirements. Note rating plates typically overestimate the amount of electrical power required as manufacturers tend to allow for some tolerance. Relying solely on nameplate ratings may lead you to overestimate the power consumption of a device.



Looking at the image above, we can see that the manufacturer has specified 275W as the maximum power consumption for this particular device. However, note that it says MAX POWER, which means that the actual power consumption will most likely be a lot less.

Nevertheless, this is a good method to get a rough estimate on how much power your appliance or device is expected to consumer.


Using a Plug-in Device Meter (Power usage meter or watt-hour meter to Measure Individual Consumption


If guessing off the manufacturer’s label (a.k.a rating plate) is wildly inaccurate then where does that leave us? What we need is a simple and cheap way to measure device consumption between the device and the power outlet. Enter the simple plug-in power usage meter or watt-hour meter!

Steplight Plug-in Power Meter

A power usage meter or watt-hour meter is a simple device you plug in between an appliance and the wall that measures the energy consumption on the fly. Even better, it will perform the calculations for you. With a power meter, you can identify inefficient appliances that consume more power, than would otherwise be expected (this may be an older appliance that could be replaced by a more Modern, energy star rated equivalent product, or a product requiring maintenance, such as a refrigerator that requires the door seals to be replaced).

  • Identify “power hungry” devices that simply consume too much energy and cost too much to  run for excessive periods (such as a plasma screen).
  • Identify and minimize “standby power” consumption from devices that consume power even whilst you are not using them (for example a microwave oven that draws power continuously to run the clock).
  • Identify appliances that are left on unnecessarily, thus wasting power.
  • Identify inefficient user practices and habits that waste electricity unnecessarily.
  • Identify faulty appliances that may be using more power than they should be.
  • Identify strategies to reduce your energy consumption


Using Clamp on Ammeter or Multimeter to measure Power Consumption


A clamp meter, also known as a clamp-on meter or clamp-on ammeter, is a device that tests electrical currents using a brace or jaws. It acts almost as a voltmeter with clamps, and these clamps can be used around a conductor to detect its magnetic field and measure electrical currents without having to interrupt a circuit or cut the wires of electrical appliances and devices. A Clamp Meter is not as easy to use as the plug-in power meter and requires more than just basic knowledge to interpret results properly. However, it can offer some great advantages over a plug-in. One of the biggest advantages is that you can measure power consumption on high current and hardwired equipment.



Most professional multimeters have a clamp on attachment such that you can clamp it on a conductor and measure the AC current passing through the conductor. The clamp meter will read the current going in to the device and also the current coming out of the device, therefore you have to separate the conductors in a power cord in order to clamp around just one conductor otherwise the current cancels itself out. An easy place to clamp on and measure the current is at the circuit breaker panel, if you remove the face of the panel you'll see a single wire going to each circuit breaker, clamping on that wire even though it's insulted will measure the current passing through that breaker and then it's just a matter of determining what you have plugged into that breaker circuit. The power is the voltage multiplied by the current and since you know the voltage is 230V, you simply multiply the current by 230 to get the power in Watts (divide by 1,000 to get kilowatts).

The most expensive multimeters will record the current over time but these are very expensive multimeters so look for ones that will hold the peak value. The cheapest ones have a data hold feature where you push a button to freeze the display on the current value, that's not what you want, you want one where if you switch on peak hold, it will simply display the peak value it's encountered so far until you switch off the peak hold. Old text books say to get an analog meter but that's because the human eye can pick out the peak values on an analog meter without any extra features and early digital meters didn't have such features.


Note from the author

We hope this article made it fairly clear how one can estimate power consumption of any device in their household or work environment. As always, we recommend that you buy a Battery Backup System (UPS) for your critical electronic equipment which will help you protect, monitor and provide backup time.

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