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Article: Power Consumption
Author: Andrew Herdrich
Date Published: 8-17-03
Since the first true Personal Computers were introduced in the late 1980's, computer users have been divided into two groups: Those who only leave their machines on when in use, and those that never turn theirs off. Those who turn them off argue that the money saved is well worth the added time at startup. In this article, I will examine the amount of power two typical systems use under a variety of conditions, and see how much they really cost to run.
To measure the actual power used by the test systems, the power flowing into them needs to be metered. This can be done using a modified power cable, as shown below. The green wire is at ground potential, and is used to ground the case of the computer. The black wire is the wire that power flows in on, at 120 AC volts. The white wire is used as a return to complete the circuit. By cutting the black wire, and attaching a digital ammeter as shown, using special test leads, the amount of current in amps can be recorded. If you would like to try this experiment at home, please note that modifying your computer's power supply systems will most likely void the warranty, and could lead to serious injury should you become a conductor to ground.
:: Test System 1
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:: Test System 2
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The cable used to test- one end fits into the power supply,
and the other fits over the end of a standard power cable.
Close up of the severed black wire- note the
use of insulated crimp-on connectors.
The power cable hooked up to the meter.
After hooking the cable to the machines, and
running the tests, I was able to create the following table based on the
results.
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Note that these prices don't include the cost to run the monitor, see the second table.
The power use is listed in watts, at 120 volts AC, so this data does not reflect how much actual load was placed on the power supply. The cost per hour/month/year is based on a standard price of $0.07 per kilowatt hour, and does not include service charges.
Watts=Amps*Volts
Cost per hour= (Watts/1000)*(7.0), in cents.
Defragging was conducted on the system partition of the hard drive, about 4Gb.
Here are the power usage statistics for the monitor:
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Based on these results, we can see that the average owner of a high-end computer system spends about $100 per year in electricity bills, if the computer is left on 24/7. This cost, however, does not figure in the electricity used by printers, scanners, and other devices. These figures are an average, so your actual bill may be higher or lower. Typical costs per kilowatt hour range from 4¢ to 16¢, depending on location, and service provider. If you choose to conduct a similar experiment on your own, please be careful. Happy figuring!
