## How much power does it take?

Having looked at a method to meter electricity differently, I decided to figure out how much electricity I was actually using. Since I deal with computers, I figured the best place to start was with my server room. What surprised me the most was how much power things took even when they were "turned off" — a lot of modern devices have clocks in them, or (PC's especially) "monitoring" circuitry, all of which takes power. Here's a quick table to summarize the results (sorted by power usage per day), with a discussion below (electricity in Ontario costs CAD\$0.07837 per kWh as of 2004 02 06):

Device Off (Amps) On (Amps) Hours/day Used kWh/month Cost CAD\$/month
Athlon 1.3GHz N/M 0.90 24 71.3 5.59
Mitel SX-20 PABX N/M 0.75 24 59.4 4.66
Pentium 1GHz 0.05 0.50 24 39.6 3.10
Pentium 700MHz N/M 0.45 24 35.6 2.79
Pentium 166MHz N/M 0.43 24 34 2.66
Optiquest V95 Monitor N/M 0.57 10 18.8 1.47
HP-2200 Printer 0.11 N/M 0 8.7 0.68
Alcatel ADSL Modem N/M 0.10 24 7.9 0.62
Netgear Hub N/M 0.09 24 7.1 0.56
Dual Pentium 350MHz 0.06 0.60 1 6.5 0.51
Back Room Hub N/M 0.08 24 6.3 0.49
TV (15") 0.06 0.22 1 5.3 0.42
USR Modem N/M 0.06 24 4.8 0.38
VCR 0.03 0.60 0 2.4 0.19
Clock Radio N/M 0.03 24 2.4 0.19
HP-4600C Scanner 0.02 0.09 0 1.6 0.13
Total 6.60 (A/d) 87.88 (A/d) 311.8 24.44

For the calculation of Watt-hours per month, I used the typical "Hours/day Used" number and multiplied by the "On (Amps)" field, and then took the "Off (Amps)" field and multiplied it by the time that it's off. Both numbers were then multiplied by 30 (days per month), and then by the nominal voltage, 110V, and added together.

It may look odd that the printer is claimed as "0 hours per day" used, but the fact of the matter is that 99.999...% of the time it's sitting idle; I might print a few pages a day, which amounts to a few seconds of usage.

Finally, the "Total" row is expressed in Amps per day in the "On" and "Off" columns.

So, in summary, when devices are left off but plugged in, it costs me CAD\$1.71 or so per month — not outrageous, but not zero either :-) Also, my average burn rate is 433 Watts.