# How do i calculate the cash im spending with a 24\day pc turned on?

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August 24, 2007 11:25:13 AM

Lets take this for example, i have a computer that im using along with a webcam to criate a time lapse video, for that i'll need that have it turned on for about 4 months with no reboots whatsoever (offtopic: its taking 1 picture each 20 minutes for a whole period of 4 months, in order to get a 5 minutes video when compiled @ 30fps\s)

And for that im using a pentium 3 450, a s3trio 4 mb agp, and a usb webcam, a small fan to refresh the webcam and no soundcard or cd drives etc. Im wondering how can i calculate the amount of euros im spending each month, knowing that the total wattage of the system is 125 watts, and my electricity company take 0.90€ per kilowatt.

Are those 125 watts the wattage it consumes per hour or something? Im only missing that in order to calculate the amount of money ill be spending.

August 24, 2007 12:27:36 PM

To accurately determine watts used, you need a watt meter. Your PSU rating is not power used.

My system has a 500 watt PSU, but idles at about 150Watts or so.

Assuming your machine really did use 125 watts, that would be per hour, so it would go like this:

125 Watts *24hrs per day = 3000 Watts used per day or 3KWhr
3KWhr * 0.90€ per KWhr = 2.7€ per day

You may want to verify your rate is 0.90€ and not 0.09€

3KWhr * 0.09€ per KWhr = .27€ per day

If your system actually only uses half that, your cost would be half.

I hope this helps.

John
August 24, 2007 12:44:02 PM

John is right 0.90€ is too high. Here in CT, US its \$0.12 and its the highest in the country. To get accurate watt reading i would suggest looking at something like Kill-a-watt. it will tell you how many KWhr you have used at the end of each week, day, hour, minute, and second. I have one and its great.
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August 24, 2007 1:24:41 PM

here in Ireland : IE (EU Country)

our Electricity is €1.25 per unit (1 Unit = KWhr) and I think the guy is in Germany somewhere cheaper, the US is cheap because of many Nuclear Power Plants that we do not have.

So living standard in EU is much more expensive than the US, hope this helps
a b ) Power supply
August 24, 2007 1:52:40 PM

You may want to eat all the food in the refrigerator first
August 24, 2007 1:57:11 PM

You where right, its 0.096€.
About the 125w value, it was kinda random, i know that the wattage displayed on the psu isnt the actual wattage being wasted, orelse i would pitty the 1k psu owners!

What i wanted to really know is that if the actual wattage being used by the system (say its 80\100w) is the wattage being wasted each hour, if so johngoodwin is perfectly correct in his calculations.

The system:

s3 trio agp card about...10 watts? (lol)
usb cam 5 watts i guess..
6 gb hdd 20 watts
cpu fan + another small fan...10 watts?

It isnt that much if in the end, but for the final effect i want for my time lapse video, i'll need it turned on for a very very long time period, hopping it wont die of cold ( not likely ) or hotness or humidity from my balcony.
The cpu has about 46% usage all the time, peaking to 100% every 20 minutes when the webcam software takes a shot, so i guess it wont wastes much electrical power.
August 24, 2007 2:07:27 PM

You also have to be careful about how they charge the electricity costs.

Here in the UK you pay a base rate and then another rate once you go over a certain limit ......
August 24, 2007 2:19:38 PM

Buy a power meter. Maplin (UK) sell one that also measures power used.

Mike,
August 24, 2007 2:52:48 PM

Quote:
Turn off everything else in the house. Wait 30 days for electic bill.

FTW!!!!

Valis
August 24, 2007 3:35:59 PM

Are there any software based power monitoring solutions?
August 24, 2007 4:10:09 PM

A Watt is a unit measurement of power, you get billed for a unit of measurement of energy such as a Watt Hour

Just make sure your units are correct in the end, and you won't go wrong most of the time.

1Watt * 1 Hour = 1 Watt Hour

or, 125 Watts * 24 Hours = 3000 Watt Hours

you can always multiply by 1 and not change anything. Since 24 hours and 1 day are the same thing, you can multiply by 24 hours and divide by 1 day, you are still multiplying by "1". your result will be a bigger or smaller number, but your units will differ.

now, 125 Watts * 24 hours/day * 30 days/month * 1 month = 90000Watt hours or 90 kWH

notice how day cancels our of the numerator and denominator and month cancels out which leaves you with Watt and Hour are the only thing left.

now multiply the price/kwh * kwh

kwh once again cancells out of the numerator and denominator leaving with nothing but the end price.

August 24, 2007 4:32:48 PM

\$.12 is not the highest in the country. Im in Houston and I pay \$.14 per Kwhr
August 24, 2007 4:57:18 PM

1 picture/20 minutes * 60 minutes/hour * 24 hours/day * 31 days/month * 4 months =

8928 photos

8928 frames/30fps = 297.6 seconds = 4 minutes 58 seconds
August 24, 2007 5:02:31 PM

I know this is just semantics, but none of you are considering the efficiency rating of his power supply at the given load. For instance: most PSU's are rated for efficiency at peak load. Meaning that if you have a 1000W PSU at 80% efficiency (one of the higher ones), then you are actually drawing 1250W off the breaker. (HOLY SHIITE!!!) Now, the efficiency can actually be higher or lower at lower loads, just depends on the quality of the PSU. Then again, who actually draws 1000W of power at load? No one with a desktop that I know of unless they're running 4x crossfire with 2900xt's. Those PSU's are just overkill or for bragging rights or to measure your e-pen.
August 24, 2007 5:10:09 PM

If you are concerned about the money you would be "wasting" by having the PC running 24/7 (like mine do), don't forget that the "waste heat" from the PC is dumped out into your room air. This has the effect of heating the room that the computer is in, which slightly reduces the load on your home heating system. So, you get to use your computer for fun things, and it even keeps your room nice & warm for you - what a deal!

BTW, don't forget to use a good UPS.

Altazi
August 24, 2007 5:16:02 PM

sepayne21 provided a good primer on doing the calculation.

The tough part is estimated the watt usage of your system. Keep in mind that the load varies and will go up from standby, sitting idle, light load, and heavy load - with gradients in between. How much you actually use the system, the loads, and your power option selections all affect the amount of power used.

Also, if doing a calculation by computing the usage of different components of your sysem, keep in mind that you have to consider the PSU efficiency - in essence the power used or wasted (mostly in the form of heat) by your PSU itself. Most PSUs operate with 70-80% efficiency - and for most it varies depending on the load. So for instance if I calculated from the other components that my computer used 300 watts at full load, then the power used by a 70% efficient PSU to provide the 300 watts would be 429 watts (300watts/70% - or 300watts/.7).

I did a quick calculation and if I used my system at full load of 350 watts 24 hours per day for 365 days per year with a 70% efficient PSU at 13 cents per KWH, the annual cost would be \$570. Glad I don't use it that much. Note that at that level changing to an 80% efficient PSU would save me \$72 per year.

August 24, 2007 5:44:23 PM

a fan to refresh the webcam?
August 24, 2007 9:43:20 PM

Yes valis, the webcam itself heats a little bit, and its turned on 24\day exposed to the sun, so i guess i little caution wont hurt.

About the psu, its a crappy 300w..
August 24, 2007 10:05:48 PM

little_scrapper said:
\$.12 is not the highest in the country. Im in Houston and I pay \$.14 per Kwhr

wow, I live in Houston too, and it's only \$0.06 per kWh
August 24, 2007 10:28:39 PM

New York is \$.18 per kwhr for the spring, and \$.23 kwhr for the summer.
August 24, 2007 11:17:50 PM

On a new machine your depreciation would be greater than the power usage.
At todays price of \$2000.00 in one year what would your PC be worth?
Maybe \$1000.00?
That would be a daily depreciation of \$2.74
The next years depreciation might only be \$500.00
August 24, 2007 11:40:24 PM

run everthing the exactly the same for 30 days and turn off the computer
then subtract one bill from the other!
August 25, 2007 12:07:37 AM

Turn everyting off in your house temporaraly. Find your Electrical Meter. Verify that it has stoped. Record the Reading. Turn you PC on record your reading again in exactly one hour. Subtract one reading from the other, multiply X 24. Refrigerator will be fine if you don't open it.
August 25, 2007 1:15:53 AM

rush_123 said:
John is right 0.90€ is too high. Here in CT, US its \$0.12 and its the highest in the country.

Move to New York - \$0.179 per KWh, highest in the continental U.S. The only higher rate is Hawaii - \$0.2055
August 26, 2007 2:54:26 AM

First, make sure the device you want to measure is turned off. Also, turn your air conditioner off and unplug your refrigerator; if they kick in while you're making your measurements, that will change the results. Go outside with a stopwatch and measure how many seconds it takes for the disc to spin around one time. Go back inside and turn on the device you want to measure. Don't change anything else at all -- turning even one light on or off will significantly change your results. Go back outside and count how many seconds it takes for the disc to go around once now.

Now you're ready to calculate. Look on the meter for something that says "Kh X.X", where "X.X" is some number (often 7.2). Plug your numbers into the following formula:

3.6 x Kh factor
----------------- = kW
number of seconds
For example, your Kh factor is 7.2, it took 60 seconds for the disc to spin once. Your check showed you were using (3.6 x 7.2)/60 = 0.432 kW, or 432 watts.
!