Computer Power Consumption Measurement Tool

An explanation of how I discovered the way to measure which was the power consumption of my computer. I created a tool of about 36 Dollars cost to measure the Power consumption of any household appliance in my home.

Saturday, October 01, 2005

Measurement of Power consumption of the rest of the house appliances.

Once I made last calculations I realized that my computer was the eating Beast of my house, Number one watts eater because he ate 56% of all the watts and .

To know how much power did the rest of the appliances consume I had to change the system because the Cable where I measured the Intensity had at one of his ends the special connector only valid just for the computer.

Therefore I went to the supermarket and I bought a simple 3 Plug with switch base where I pealed the cable and took out and separate the phase, neutral and earth wires as I did with the computer cable.

With this system you can just plug any appliance to the base and see how much intensity and therefore power does it consume.

For example a 100 W bulb consumed in my house 0.35 Amperes wich meant that was really consuming ( 232v x 0.35 A) = 81 Watts.

This way you can measure the rest of the appliances power consumption in your house.

One interesting calculation that I still haven´t done is how much Standby power consumption have t my TV, VCR, DVD. That will be my following calculation.

But if you want to see an already made calculation you can click on the links bar "Standby power Study" to go to the page

Answer to my question, My Pc eats 56% of the Watts I buy in a year.

After achieving to measure the standby consumption of my pc I started measuring the power consumed in different conditions.



Here are measurements results for every item in my computer.

(Voltage 232 Volts) I(A) Total Watts
Standby conditions (Wstdb) 0,92 214 214
I(A) Total Watts Watts/item
fan1 0,93 216 2
fan2 0,93 216 2
fan3 0,928 215 1
fan4 0,93 216 2
CPU 1,08 251 37
VLC 0,95 220 6
CDROM 0,99 230 16
DVDR 0,98 227 13
TUNEUPQM 1,07 248 34
BFVno fan 1,11 258 44
BFVwithfan 1,13 262 48
BFVpeaks 1,18 274 60

As you can see playing games like battlefield vietnam uses extra 60W above the standby power consumption (214W) because it uses , cdrom, videocard and cpu resources.

My minimun PC Consuption is 214 Watts and I reached peaks of 274 Watts.


To translate this to money you just have to know how much does the kwh cost and use the following formula.

Money Cost = kwh price x watts/1000 x hours of usage.

In my case:

KWH Price 0,0830 €

Days/ year usage of PC

Average Consumption PC
220 W

Day 24 5,28 0,44 €
Month 700 154 12,78 €
year 8400 1848 153,40 €

PC Kwh Consumption per month 154 KWH
Month Average Total electrical Kwh 275 KWH


Due to the fact that my computer is only 15 days turned off in a year that means that I have to pay 153,4 euros per year and this means also that my PC eats more than 50% of the electricity I use in my house.

It is pretty amusing and revealing answer for the questionI made up my self that day.

Here comes how I finally measured the Power.

First of all I checked a couple of electrical concepts and formulas to know what i had to do.
Power is measured in Watts and it is the product of Voltage (Volts (V) times Intensity (Amperes (A))
In a monophasic net like in my house the formula is this.

Instantaneous Power consumed P(W) = V (V) x I(A)

Therefore to measure the power I need to measure voltage and intensity.
To do this you can use a the cheapest Digital Clam
p Meter in the market which costed me 31 Euros. in june 2005 in Spain.

With some digital clamp meters you can measure both voltages and Intensity like in the one I bought..

To know the exact power consumed you must check before the voltage in your house net because this may
vary +- 5% from the national standard and also will be different in the morning and at night.

In my case National Spanish momphasic voltage is 220 V. As you can see in the picture below my measurement was 232 Volts at 16:54 hr.

Finally Needed to check the incoming intensity to my computer. To do this we need to use the Clamp meter over just ONE phase (or one cable) due to the measuring phisical concept in which is based.
The power supply cable of my computer has 3 Wires. Neutral, Phase and Earth wires. If we apply the clamp meter around the three of them we won´t measure anything. That´s why we need to peel the isolating outer protection to take out the three wires and apply the clamp meter to only the blue wire or phase wire as shown in the picture.

once we have done this we just have to plug the cable to the computer turn on the digital clamp meter on the smallest scale setting (20A in my case) and use the following formula to know the instantaneous consumed power.


As you can see in the picture my PC consumption in standby conditions (without the monitor) and without the cpu working, any cdrom, dvd, disconnected form internet and just with the desktop view was 0.92 A.

Therefore my PC consumption in Standby condition is 214 W.
P(W) = 232 V x 0.92 A = 214 watts.

The cheapest way to measure Power Consumption

There is one way to measure the electrical power consumption of any appliance in you house totally free.

Using just your watch and the electric meter outside your house, you can accurately and safely measure the power consumption of various household appliances and devices.

It is described in the following link:

This method is OK but the final value of the power measured comes out of a formula and a calculation and I wanted to see the values with my own eyes as I said before.

Searching for already made Measuring commerial Tool

Once I realized about this fact, I started to find a commercial tool which I could buy and use it to see in Watts units the momentaneuos eaten power.

After searching and searching I could just find a single picture of what it seemed to be the Tool I was Looking for.
It had a 2 pin male plug and
on the opposite side a female plug with a display . It seemed to work by plugin it to the electrical net and on the female plug the power consuming appliance. At the time that you turned on the appliance the display would show you the instatnatenous power consumed in Watts and would also record the maximun and minimun values reached.
This is the tool I wanted to get to answer my question.

But where could I find it?. No idea. I tried to find it in my town local stores like Carrefour, Media Market, Leroy Merlin etc.. but no one had this measurement tool.

So once I failed to find it in local stores and internet I figured out how to build this tool with other electrical tools.

If you know where to find this tool please send me a comment to le t me know it. If you don´t know and you also want to measure your house appliances power consumption keep reading my following entries.

I need to get a power measurement tool

After making myself this question I started searching in the web how many watts was my computer eating.
I found some webs where I could calculate the power consumption just by defining my internal PC components and hitting the calculate button.


This method didn´t answered my question because it is a calculation of the maximun power consumption you can have with your pc components runnig all of them at the same time and it is just helpfull to determinethe
minimun power supply requirements for your installed components.

I wanted to know the realistic average consumption of my pc and see it with my own eyes and not just just a calculation of the Power consumption based in some specific conditions.

Welcome Myself

Yeterday I went out with some friend to have dinner and in one of those conversations with one of my friends, I finally came home believing that publishing one blog would be a good Idea.

My Blog is going to describe how I answered myself to the question of , How much money do I spend in a year having my computer turned on 350 days 24 hours a day?.