kill a watt?

Jim Lux James.P.Lux at
Thu Mar 13 10:22:15 PST 2003

At 09:36 AM 3/13/2003 -0800, Jim Meyer wrote:
>On Sun, 2003-03-09 at 16:35, Jim Lux wrote:
> > Sure, it'd be nice if it had an external interface, but then it would cost
> > $500+, if only because it's a line connected device, and you'd have to
> > provide isolation, etc.  There's a web site out there where someone took it
> > apart... everything is floated at line voltage inside (which makes it muy
> > cheap) much like X-10 stuff.
>Heck, at the $45 price RGB noted, you should point a cheap webcam at it,
>take pictures at some reasonable interval, and write a script to OCR the
>pix and parse the output for monitoring.
>But maybe I'm just geeking for the fun of it. =]

Actually, this is a really good idea... the web cam is $20, the Kill-a-Watt 
is $40..

The only problem I can see is that you might need to push the buttons on 
the Kill-a-Watt to cycle through the modes.

Another inexpensive approach is to transformer couple the current and 
voltage on the line into the L&R ports on a sound card, grab a tenth of a 
second of data, and do all the power quality calculations you want.  If 
you've got three phase power, you need 6 or 8 channels, which makes it a 
bit trickier.. but you'll be able to see if you've got circulating harmonic 
currents, etc.  Anyone ever synchronized multiple sound cards across a cluster?

The current transformers are $20, the voltage transformer is $10 (brand 
new, Qty 1 prices.. surplus can do MUCH better)

James Lux, P.E.
Spacecraft Telecommunications Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875

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