How Much Power Does Your Wall Wart Draw??
On the NPEN technical session on 2/15/01, the question was asked "Is it OK to leave my portable's wall wart charger plugged in when it is not charging the HT?" We discussed a couple of reasons why you might not want to do so, such as the threat of lightning damaging it or the output being accidentally shorted and frying the charger. I begin to wonder just how much power a charger does draw when it is not charging. My WAG was "about the same as an electric clock", but I decided that a more definate answer was appropriate. In my collection of old, large junk, I had a rack mount low wattage meter, so I dragged it out, put some power leads on it and proceeded to measure some things.
Starting at the bottom, my inductive coupled electric toothbrush charger pulls 0.4 watts without the toothbrush plugged in and 0.6 watts with the toothbrush charging. The cost at my residental rate makes this .11 cents per day or about 3.5 cents per month since it spends most of it's life plugged in.
By comparison by wall wart HT charger draws 0.8 watts plugged in and 1.5 watts charging an already charged battery. The "drop in" charger for the same HT draws 1.3 watts in "standby" and 2.1 watts charging the same HT. So my cost for leaving the wall wart plugged in all the time is 4.6 cents per month in "standby" or 8.5 cents with the HT on constant charge.
An electric "old fashion" clock draws 2.6 watts or 14.8 cents a month. An LED digital clock required 2.9 watts for 16.5 cents a month. So the HT wall wart uses about one fourth to one half the electricity that an electric clock depending on whether it is charging the HT or not. I guess we can conclude that the cost of operating the HT charger is pretty low.
For comparison, a VCR plugged in but not turned on uses 6 to 10 watts (three units tested). Turned on but not running a tape required 14 to 17 watts. Note: the clock was NOT blinking for the measurements so this may be unrealistic for some households!! So turning the VCR off when not in use saves 46 cents a month (off 34 cents, on 80 cents).
Therefore you can charge 6 to 9 HTs for the cost of one VCR or about 2 HTs per electric clock. I knew you would be interested!!! Doing this did prove one thing to me. One of my wall warts had a broken wire.. No wonder the battery on that HT wouldn't stay charged. A true charging indicator certainly would be nice - - and that may be the subject of another article since many "chargers" which do have indicators only indicate that the charger has power, NOT that is is charging the device. Till next time, k4rka...
Back to features archive
