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I approve of the Kill-A-Watt meter.. my experience

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Posted by itsme.ultimate on December 17, 2005, 10:45 am

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Just a while ago, I started a thread comparing the Kill-A-Watt and the
Watts Up? power meters.

I'm not representing either companies, but based on my personal
testing, I approve of the Kill-A-Watt meter.

Comparing the Kill-A-Watt and the Watts Up?, I observed that the watts
up read about 10% higher than Kill-A-Watt.

Now I compared the Kill-A-Watt against a professional power
analyzer(Valhalla 2101)  and the kill a watt is only off by no more
than a percent(relative to Valhalla 2101) , except in single digit
watts and >1,000 watt.

They were connected in series and tested using many types of loads:

Unity - 300W light bulb
Half-wave rectified - halogen lamp dimmed with a diode
Reactive - (DPF or cos theta)  80W fan
Harmonic load - (PF, distorted current waveform) 75W computer
High crest factor - Full range dimming of a 300W tungsten lamp while
monitoring power

Under all conditions, Kill-A-Watt was within a percent from the
professional power analyzer with a used price tag of ~$00

The Kill-A-Watt is an amazing piece of instrument with great accuracy
for only $0.

very good user interface
lots of fuctions

Can't use with inverter/generator.  When I connected to a modified
squarewave inverter, the resistive voltage divider for powering the
device got very hot.  (the package said not to use with a generator or
inverter, but I think that has something to do with the power supply,
which is simply a series combination of a resistor and a capacitor. If
you can modify that part, I think it would work well with any power

Sensitive to inductive kickback:
if you're measuring cumulative kWh, it resets itself from time to time
from inductive kickbacks from the load such as a refrigerator.

No memory:
if power is lost kWh recording is lost

Watts Up:

Holds kWh value if power is lost.
Can hold peak value for power and current
RS-232C in the Pro version
Can be used with a generator/inverter

Expensive $00 for basic, $40 for Pro, $00 for Pro ES(premium)
Not very accurate, particularly with inductive and harmonic loads.
Small screen
Not as many display values as Kill-A-Watt. You can't see VA in real
time, but you have to multiply the V and A yourself.

Based on a  current transformer rather than a shunt even though the
upper limit is only 15A.  Current transformer introduces error and is
usually used when accuracy isn't needed or you can't splice into the
wire (i.e. AC 2,500A three phase measurement using three current
transformers, because you can't just cut those primary wires going into
a 12470 substation transformer)

Posted by m Ransley on December 17, 2005, 11:18 am

I use mine on a Generac 7500 fine, except on startup it almost fried. I
use it to check Hz and V amp and watts. Be sure gen is at speed first,
but mine is not an inverter style. From what I read yes they are
accurate. Nice tool.

Posted by Steve Spence on December 17, 2005, 1:54 pm

itsme.ultimate@gmail.com wrote:

I use my KAW both with my inverter and my generator (we have no grid),
the numbers are the same for my fridge and other devices regardless of
what's providing the power. I do wish it would remember it's values, as
I lose everything when I switch from gen to inverter daily.

Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net

Posted by Daniel Armstrong on December 19, 2005, 11:22 pm

I had a wireless doorbell receiver that started smoking when I plugged it
into a MSW inverter.  It too was based on a resistor and capacitor.

Posted by Steve Spence on December 20, 2005, 2:51 am

Daniel Armstrong wrote:

I have not had anything smoke on our MSW. I'm betting there are good
MSW's and worse MSW's.

Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net

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