Fast on the heels of my energy-on-the-brain week in San Diego, I decided to run some experiments with my recently acquired Kill-a-Watt to debunk some myths about consumer electronics and power consumption. What follows is by no means exhaustive, but I figured I would write it up as it has frequently been the topic of lunchtime conversation at the officeâ with people arguing both sides of each argument as though it were politics and not simply electricity 101.
The basic statement that I was trying to confirm or disprove was that your computer/cellphone/ipod/etc. charger sucks electricity even when it is not connected to a device. Savvy environmental marketers have called this the "vampire effect" or the problem of "phantom power," and truth be told, after I first heard the term, I could never look at one of those cuddly black bricks the same.
So I went around the house looking for as many bricks as possible, putting my Kill-a-Watt between them and the wall source of power and then connecting and disconnecting their associated devices. An aside: For those that don't know what a Kill-a-Watt is (pictured here), it's one of several cheap gizmos you can buy to plug between a given appliance and the wall to measure how much power is being consumed. I'm not quite sure how it works, but quickly testing it on both 60 and 100 Watt lightbulbs convinced me that it worked as billed.
The result: for each of the 13 bricks that I tried, ranging from a wireless phone charger to a MacBook Pro power adapter, the vampire/phantom thing is complete BS. The moment you disconnect the associated device the Watts measured on the Kill-a-Watt go right down to zero. Interestingly enough, this is equally true for low wattage chargers like the iPhone one (~1-2W while charging). It makes senseâ after all I'm fairly certain that a fairly cheap circuit on the power adapter can get a good sense of load and just cut the whole power supply off if nothing is connected. As a funny aside, it seems that there is a whole category of "smart powerstrips" that are sold to protect the user against this bunk phantom power thing.
Since I had the Kill-a-Watt out anyway, I then went on to try to prove one of my own wacky theories: that you could actually conserve overall power when using your laptop at home by a) pulling the battery out when you were connected to the outlet and b) never leaving the machine connected after it was fully charged.
My theory about pulling the battery out went something like this: if a machine consumes X amount of power just to run, then also charging the battery at the same time must require X+Y power where Y is whatever it takes to charge the battery. And to point b above, even when the battery was fully charged, there would still be some amount of power required to trickle-charge, or keep the battery topped off.
However, in my very simplistic testing, it seems that with or without battery attached, my MacBook sucked in about 20-30 Watts pretty constantly (the variation being most directly affected by the display brightness). I tried it with 50% charge in the battery, 80%, and even 100% and it just seemed to hold constant in its power consumption in all cases.
Which of course leads me to wonder where the incremental power to charge the battery comes from. My current guess is that the Kill-a-watt does have some standard margin of error (that I didn't see with my lame lightbulb tests) and that this is where the incremental power to charge is being missed.
To end on at least one energy saving tip, for a typical MacBook in sleep mode, the cost of trickle charging is about 1-3 Watts which means that unless you are going on a long airplane ride the next day (or are a power hygiene freak who must have all devices at 100% charge all the time), you will save a little bit of power by pulling the adapter from the machine (though not unplugging it from the wall) when the little charge light turns green.
Whew, ok. With that behind us, I promise to get back to InterWebs topics tomorrow!PS, if anyone knows of a relatively cheap device that can act as a Kill-a-Watt does but store data points over time for subsequent analysis on a computer, please let me know. My next set of experiments requires more than just eyeballing the display as the junk attached sucks power.