- 1W: cell phone charger
- 3W: motorized lamp timer
- 4W: weather station
- 5W: two laptop-computer charger units (while not connected)
- 5W: three strings of LED christmas lights (OK, it's seasonal)
- 10W: phone answering machine
- 12W: alarm system control box
- 40W total thus far.
This total is the tip of the iceberg, because it does not yet include the big vampires: CATV, TV, stereo. Of course, the lights, furnace, fridge, range, laundry, and outdoor lights are the big consumers.
The term "wall wart" is something I heard once a long time ago: the little plastic plug-in transformers are like warts growing out of the wall outlet. and they are vampires, because they suck juice from the wall outlet, often doing so even if they are not plugged into their companion devices.Experimental equipment.
I have my ancient trusty Fluke 8060A digital multimeter. In years and years I can't recall that I ever measured AC current with it. Until now! I rigged up an AC plug and AC receptacle cord, and sacrificed an old Fluke lead-set to put the meter in-line with the hot lead (the lead coded black). The OEM leads provide good insulation on the plug ends. Sadly, this DMM's AC current limit is just 2 amps AC. But for wall-warts, that's enough!
Method:
Plug the device into the wall using the Fluke DMM AC current measurement scale, and adjust the scale multiplier from high to low scale to obtain the most precise three-digit measurement. This Fluke DMM is very precise, more than needed for this type of measurement. AC current is measured using RMS (root-mean square) measurement. Power (watts) consumed is computed as the current times voltage. Either the line voltage is measured and recorded or is assumed to be similar to earlier readings. (My house it was measured as 121 and 122 VAC 60Hz, assume nominal 120V)
It is important to measure the AC power actually consumed at the wall outlet connection, rather than measuring it on the consumption (DC) side. I'm curious to see if some of these devices are "inefficient." Name-plate ratings for power (wattage) and current usually tell some, but not all, of the story.
Template:
- Device. Manufacturer, model, nominal name-plate rating of the wall transformer, other data.
- Current: the measured current on the AC line side, 120 Volts AC nominal, 60Hz.
- Power: computation: watts = current x voltage.
- Usage: describes how much time in each day this device is plugged in, drawing power.
Measurements.
- Device: Nokia cell phone charger: Bought in 2006 for model 6162i cell phone. Wall transformer rated as 100-240VAC 180mA. Output is 5.7VDC 800mADC.
- Current: measured without the phone plugged in, draws 5.7mA. While a quiescent, almost-charged cell phone is plugged in, the draw varies every few seconds 65mA - 85mA AC.
After unplugging the phone, the quiescent no-load current dropped inexplicably to 2.4mA AC. Clearly there is some sort of "smarts" in the charger. - Power: 0.70W quiescent (no phone).
- Usage: This typically is plugged in 24/7/365 even if the phone is not charging.
- Device: Wireless weather station: Davis Vantage Weather-Pro 2. Wall transformer rated as 120VAC 5VDC 200mA.
- Current: measured while in use28.8mA AC line, with "lamps off." If the "display lamnps" are turned on, it goes up to 31.2mA AC.
- Power: 3.54W (or 3.83W with lamps on)
- Usage: This runs 24/7/365. Only reverts to battery if the power fails.
- Device: VTech answering machine with wireless phone: base stations. Wall transformer rated as 120VAC, ??? mA AC.
- Current: 85mA AC with no phone sitting in the charger base. When a (mostly) charged phone was placed in the charger it pulled 91mA AC but this draw depends entirely on the charging cycle. AC line assumed to be 122VAC.
- Power: 10.4W (no phone in base).
- Usage: This is plugged in at my house 24/7/365.
- Device: mechanical plug-in timer, Intermatic "Time All" model SB811. This is the type that is motorized, not electronic.
- Current: 22.7mA AC.
- Power: 2.8W.
- Usage: I have one plugged in 24/7/365 to control a lamp.
- Device: Charger for Sony laptop computer, model VGP-AC16V8. Ratings 100-240VAC@1.5A; output 16VDC @ 4A bought around 2005. It has a little green LED that is lit as long as it is plugged in.
- Current with no connection: 18 to 22mA AC.
- Power: 2.2W to 2.7W.
- Usage: I have one or two of these plugged in, idle, a lot of the time. OK, almost all the time: one in the famliy room, one in the bedroom.
- Current when plugged into half-charged laptop, while streaming a vdeo program, fan is operating, display (12" LCD) brightness is set to 3 of 8:
approx 500mA AC. - Power: approximately 60W.
- Usage: perhaps a few hours each day.
- Device: LED christmas light string (3). Each string has 35 bulbs, total 105 lamps. The box says Westinghouse; the label says "Holiday Creations Ltd, item 34417." The "bulbs" are little plastic globes about 1cm diameter in red, orange, yellow, green and blue.
- Current: an amazingly low 42 mA AC (for three light strings)
- Power: 5.12W for three thrings (105 bulbs)
- Device: Alarm system: a home alarm with wireless sensors, call center monitoring, professionally installed by one of the top three nationwide alarm monitoring companies. The alarm control box is about 15 years old, and is powered by a chunky wall-mount transformer. Rating primary 120V 0.14A, secondary 14VAC 1.4A. This is not a DC converter, just a raw transformer.
- Current: measured with system idle: 100mA AC. While alarm is "talking" and reporting status: 120 mA.
- Power: 12W to 14.4W.
- Usage: This is plugged in all the time 24/7/365
Up next for measurement, things at my place and other people's homes: Compact fluorescent lamps, night light, light bulbs, light bulbs on dimmer, Comcast cable TV box, TV set, stereo, alarm clock, computer, computer monitor (CRT).
