Inside Kill A Watt
Cafe Electric llc. Hacking Division
The Kill A Watt is a nifty power measuring device for home use. It's cheap and available online. See them on eBay below.
It measures Voltage, Current, Frequency, Watts, VA, Power factor, Hours plugged in, and Kilowatt hours. The instructions are minimal but also unnecessary because, like a Apple computer, it's simple to set up and use.
This unit caused much speculation about how it could be done so inexpensively, so here for your enjoyment are pictures of the inside.
It seems that R17 is the current measuring shunt, U1 amplifies it for the processor. Recognize the processor? I don't. let me know if you know it.
Accuracy is not so great, as mine shows 0.04 VA with no load connected. Fortunately the Watts reading does not suffer from the same offset so it must be symmetrical It also reads 59.9 HZ which is wrong. But overall it's damn good for under $30.
Click on images for a much larger image.
Check out auctions and sales of Kill A Watts here: