Kill-A-Watt Re: measuring power usage

Jim Lux James.P.Lux at
Wed Jun 4 00:25:19 EDT 2003

I know someone who has reverse engineered the Kill-A-Watt, as well as done
extensive testing at various power factors and waveforms.  The thing really
does measure actual instantaneous power (averaged over a few cycles), so
weird current waveforms, etc. don't fool it.  It definitely measures active
power vs apparent power (RMS V * RMS I) as well as other parameters..
Accurate to a few percent, which is substantially better than most
inexpensive DMMs.

> >Yes, very lovely thingie.  There are links to at least one source on the
> >brahma vendors page, and I >>have<< pictures of a kill-a-watt in action,
> >if I ever overcome my innate inertia and post them on the brahma photo
> >tour...
> There is nothing in the flier that indicates that it measures rms amps and
> hence rms watts. Computers are not resistive loads and they draw current
> a switching fashion. As a result they usually produce a lower current
> reading on a non-rms meter than they are actually using. From memory the
> measurements I did produced about a 20% difference in current measurements
> between Fluke rms and ordinary meters.

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