# Need help with Kill-A-Watt meter

Discussion in 'Electronic Basics' started by Peabody, Feb 28, 2013.

1. ### PeabodyGuest

I got the Kill-A-Watt P4400 meter today, and just need a little
help with what the display values mean. (This is all AC, and I
never quite imprinted on AC.)

So what I need to know about any device is the rate of KWH it
consumes - because that's what I get charged for. The button on
the right displays the total KWH the device has consumed since it
was plugged into the KAW, and the total elapsed time. From that
you can calculate how many KWH it will consume per day, month or
year.

But for devices that don't cycle, I assume I could just look at the
instantaneous Watts value and calculate from there. Right?

However, it also has:

RMS Volts
RMS Amps
VoltAmps
Power Factor

Are any of these useful for calculating a device's cost to operate?
If so, how would I use them? It seems to me all I need is Watts,
or KWH over time for cycling devices.

Thanks

w.

3. ### EcnerwalGuest

If that's all you want to know, spiffy, ignore the rest.
-----
No, really, "Ethel, don't look..."
-----
"...but it was too late. She'd already been zowwed."

Volts is pretty much "is power service OK." Hardly ever needed, though
it might help you check that a portable generator was in range if you
were using one. Quite rare for it to be out of range if you have power
at all.

You forgot Hz, which is frequency, again, mostly useful for checking a
generator. If the power frequency provided to your house by a major
utility is actually off, go buy a lottery ticket. If the KAW readout
says it's off by a little, it's the KAW's low tolerances 99.9999% of the
time.

VoltAmps are volts times amps, and how different that is from watts is
power factor. For the home user (and KAW is a home-user oriented device)
it's primarily of use to figure out what-size UPS you should buy for
your computer and/or network hardware. A 100W device with a 200VA (0.50
power factor) will need at least a 200VA rated UPS to run it.

Larger power customers actually have incentive to improve power factor
(closer to 1.00 is better) in the form of lower costs. Home users
typically get a free ride. If you have a generator or UPS, improving
your power factor will be in your self interest for the items you run
from those power sources.

If you haven't already noticed - the main reason you want to pay
attention to the KAW clock is that the KAW resets on the briefest of
power interruptions. So if you leave it for two weeks, make sure it
counted for two weeks. It would be nice if it would hold time for a
minute or so, but it doesn't.

After the initial surge of checking everything, it may get more sporadic
use, but it is nice to have. Most recently used mine to see what a new
computer build was actually using as it ran. When I had it plugged into
my desktop, I could tell when newswatcher hung on exit, as the power use
would rise. Of course, after a few seconds of that the fan noise
increases, and if you've grown to expect the occasional hang-on-close
you look for it, but it was amusing to note.

It does make me yearn for a 240V version from time to time. I actually
put a Murata readout (does not total KWH, but provides volts/amps/watts
and PF) on my well-pump for monitoring. I can roughly equate the water
depth to the amps/watts, and hope to be able to spot signs that the pump
is going bad before it actually dies (though I also plan to put a new
pump on the shelf after 5-7 years or so, in order not to be panicked
into buying one in a hurry at high cost.)