Power usage

If you live in Romania, you might have one of these at home:

And you may want to use it if you don't feel like buying a wattmeter for like, 100-150 RON, since you're a nerd, and aren't afraid of using measurements and unit conversions to get to the result.
Well, you're in luck, my friend, since I made a spreadsheet that can calculate that for you.
Simply copy the spreadsheet and replace my input numbers (in the yellowish boxes) with your own (and extend the formula fields if necessary, and the averages' ranges in the Notes column).


I explain each field:
  • On (sec/rot) - Time of the meter's disk to do a full rotation, in seconds, when the device is on
  • Off (sec/rot) - The same, but when device is off/unplugged
  • On (rot/sec), Off (rot/sec) - Computed inverse (speed instead of slowness)
  • diff (rot/sec)diff (rot/h) - Difference in speed between when on and when off
  • Usage (W) - The usage of the device. If you have a digital power meter, which shows you the current current usage :D then you don't need the previous columns.
  • Cost (RON/h), Cost (RON/month) - The hourly and monthly cost of running the device continuously
  • Price/kWh (RON) - The price of electricity per kWh: get this from your power bill, it may be different than mine
  • Rotations/kWh - The number of rotations your meter's disk performs for each kWh (you'll have to trust the meter)
To measure most accurately, alternate the On measurements with the Off ones, so that when something is turned on and off, you notice it (the Off time changes drastically). I marked the rows where this happens excessively as outliers, with red, and ignored them in the final averages.

Use a precise timer, that can show you tenths of seconds, and make sure you stop it at exactly the same position of the disk as you started. I used the end of the black line on the disk edge as a reference; that way, I could see exactly how close it was to the end.

Also, you should preferably perform the measurement at night, when there are no other people awake to turn other things on and off.
I found out that my old Pentium 2 uses about 27W when idle, and 40W when booting/busy.
Also, my laptop uses 13W when idle, 43W with 1 CPU core fully used, and about 50W with all 4 cores at 100%. So, more incentive to use multithreading :)

I needed this to find out whether it's worth leaving my old home computer on, as an internet proxy through which I could play games on any ports. Turns out it's not worth it (~60 RON/month, might as well get mobile Internet at that price). And I'm glad I did this calculation, because I saved endless power.