A few months back I ordered and received a “Digital Utility AC Power Consumption Monitor and Timer” from DealExtreme (find it here). I just started playing with it today. The photos below show the front and back — it is a PMM2010 from DEBUY (which probably doesn’t mean much to anyone, it certainly doesn’t to me), rated for 220V AC mains supply and maximum 10A load. You plug the PMM2010 into the mains power supply, and your appliance into the PMM2010.
Although technically built to the Chinese standard, the power pins on the rear are sufficiently similar to the Australian standard that I could plug it in to a number of wall mounted outlets and power boards.
The third photo is a picture of the English-language user guide — it refers to a PMM2206 and PMM2210, but I believe the PM2010 is equivalent to the PMM2210. The most important piece of information is that the left-most push button resets the unit if held for 5 seconds, and the right-most push button cycles the display through a number of modes. (For example, one click from the initial display gets you the current average power consumption in watts.) The unit keeps track of time, and can also display kWh per hour, per day and per month.
I’ve run a number of simple experiments to get an approximate sense of the unit’s accuracy.
A 20W desk lamp
Plugged in my small halogen desk lamp, whose base claims it is a “20W max” @ 230/240V unit. The PMM2010 recorded 22-23 watts average load after 4-5 seconds, which continued consistently for a number of minutes.
After turning off the lamp the PMM2010’s reported power load drops to zero within 4-5 seconds. Turned lamp back on, and over 4 seconds the average load cycled up, peaking at 31W then dropping back to a constant 23W.
A 25W soldering iron
Plugged in my small 25W 240V AC soldering iron, and over the first minute of operation, the PMM2010 registered pretty much spot on 25W average power draw.
A 2200-2400W electric kettle
Our current Breville electric kettle is rated 230-240V & 2200-2400W. I put 500ml cold water in it (the minimum amount) and turned it on. Power draw was measured fairly consistently at 2440-2450W throughout the entire period (cold water to boiling water).
After the kettle had boiled, the power meter reported a total “0000.05” kWh total watthour energy draw from the boiling process (readout from the PMM2010’s initial screen). This corresponds to roughly 60*0.05/2.440 == 1.2minutes of kettle operation (and seems about right, allowing for the resolution of the kWh reading).
A 1050W electric toaster
Our current Breville two-slice bread toaster is rated 230-240V & 960-1050W. I toasted two slices of regular white bread and saw a power draw of relatively constant 1040 to 1048W for the entire period.
The toasting completed in roughly 2 minutes, and the PMM2010 reported 0000.04 kWh total energy consumed.
A Cisco WiFi AP & IP Phone
Currently at home I have a Cisco 7960 IP Phone (mains powered) and Cisco WiFi AP (configured to create a VPN tunnel back to my work). These two are sometimes left turned on all day when I’m working from home.
When both units are idle their combined power draw is measured as 11-12W by the PMM2010 (i.e. the IP phone booted up and then quiescent, the WiFi AP being otherwise unused except to provide a tunnel for the IP phone’s signaling traffic). This power draw is consistent over 30 minutes. Picking up the headset on the phone (getting ‘dialtone’) makes no noticeable change in power draw.
An R700 Toshiba laptop running Windows 7
When idling (laptop off, battery charged, power supply basically just topping-up the batter) the power draw was between 0W and 1W, i.e. almost too low to register on the power meter.
Opening the lid (resuming from sleep mode) saw a spike in power draw as the machine powered up & hard drive spun up. Draw was fluctuating over 20-30 seconds from 24W – 30W, before settling down to a steady 12-13W with the laptop sitting at the login screen.
Logging in saw the power spike briefly (over 10seconds) to 19W then settle back down to 12-13W while the laptop is idling (with screen lit).
Charging an iPad 2
I had access to an iPad 2 having 75% battery charge. With the iPad 2 switched it off, I plugged it into the Apple USB charger, and the charger into the PMM2010.
The iPad beeped and the screen briefly lit up to acknowledge that charging was now in progress, and after letting the readings stablise for a few seconds the PMM2010 reported a stable 11W power draw for multiple minutes.
Other information online
There’s some excellent information and photos from a Brazilian site here (or here, via Google Translate). According to this site, the PMM2010’s power measurement chip is apparently an Analog Devices ADE7755.