The other day I became curious about how much power was being used by various electrical appliances in my house. In particular, I was curious about “standby power” or “vampire power”: the electrical power drawn by devices when they are idle or even completely turned off. So I
stole borrowed a digital multimeter from work, connected it to an extension cord (had to cut open the cord), and voila–my own power meter! To get the power usage in Watts, I measure AC current (amps, rms) and multiply by 120 volts.
The results surprised me!
First, the good news: the little power supply that I use to recharge my cell phone is actually quite efficient. With no phone plugged into it, it draws only 0.0009 amps, for a power consumption of about 0.1 Watt. At 10 cents per kilowatt-hour, that works out to about 10 cents per year. I still unplug it when not in use, just out of habit, but leaving it plugged in clearly wouldn’t ruin either me or our planet.
Next, the bad news. Many other power bricks were very inefficient, drawing 4 to 6 Watts even when hooked up to no load! Other appliances clearly have similarly inefficient power supplies inside them, like my Braun coffee maker, which draws 3.5 Watts even when it’s turned off–all to run a stupid little LCD clock which I’ve never even bothered to set to the correct time. Other losers were a boom box (6.8 watts when off) and a pair of computer speakers (7.9 watts when off).
Why are some of these so bad? The answer, unfortunately, seems to be just bad design. Old style power supplies often use transformers to step down the voltage from the 120 volts in a standard outlet to the handful of volts needed for the appliance. These are the large, heavy black bricks that often feel warm to the touch when they are plugged in. By contrast, the small power brick for my cell phone feels very light; it uses silicon-based electronics instead of the heavy iron-core transformer, and is much more efficient. When the phone isn’t plugged in, the power supply doesn’t feel warm at all.
But the single worst offender was my cable box, made by Motorola and supplied to me by Comcast. When it’s on, it draws 35 Watts. But when it’s off, it still draws 34.5 watts! That’s costing me an extra $30 per year, for absolutely no benefit to me. That’s unconscionable!
The solution is simple: I have now put several of the worst offending devices on power strips with off switches. Now when they’re off, they’re really off. 🙂 With a small amount of effort on my part, I should easily be able to save about $70 per year, which of course also reduces my carbon footprint and is generally good for the planet.
Do you have a story or question about “vampire power” you’d like to share? Leave a comment and let me know.