Re: Basic AC wattage question: am I doing my math right?


"redbelly" <redbelly98@xxxxxxxxx> wrote in message
news:aeae9a31-d820-4d8d-a30d-2a4e5f15c554@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

You can beat the 1W resolution by doing a kWh measurement. At 2W,
you'd need to wait about a day with the Kill A Watt to get to 0.05
kWh, from which you'd calculate the power to +/-20% accuracy
(resolution of the Kill A Watt is 0.01 kWh).

Of course, the OP must be willing to go one day without turning on the
TV.

This may not really help, if the basic resolution and zero offset errors
compromise accuracy. The integral of a large number of bad readings will
just give a bigger bad reading. If the system is analog, multiplier
circuits are often non-linear at low levels and have offsets. A digital
multiplier is limited by the resolution of the A/D components. When you are
operating at two bits, you can have an error of -50% or +33%.

An alternative way to measure the actual power consumption would be to
enclose the TV in a well-sealed styrofoam box, and measure the temperature
rise above ambient to a point where it reaches a steady state. Then repeat
the test with a resistor, and adjust the power until it produces the same
temperature.

This will work with any waveform. But perhaps if there is an RF component
that is radiating energy through the enclosure, it may draw more power than
is measured by heat generation. The heat is simply wasted energy, assuming
you don't want a heater. Along the same line of reasoning, if you use
electric heat, and it is being used, the TV does not add anything to your
utility bill. It may even reduce it if you have the TV under the thermostat
and you don't change the setting.

Paul


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