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

Author

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

itsme.ultimate@gmail.com

2005-12-17, 7:21 am

X-No-Archive: Yes

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 ~$500

The Kill-A-Watt is an amazing piece of instrument with great accuracy
for only $30.

Pros:
cheap
accurate
very good user interface
lots of fuctions

Cons:
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
source)

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:

Pros:
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

Cons:
Expensive $100 for basic, $140 for Pro, $200 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)

m Ransley

2005-12-17, 8:21 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.

Steve Spence

2005-12-17, 10:21 am

itsme.ultimate@gmail.com wrote:

>
> Cons:
> 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
> source)
>

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
http://www.rebelwolf.com/essn.html

Daniel Armstrong

2005-12-19, 8:21 pm

"Steve Spence" <sspence@green-trust.org> wrote in message
news:43a417cb$1_2@newsfeed.slurp.net...[color=darkred]
> itsme.ultimate@gmail.com wrote:
>
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.

Steve Spence

2005-12-19, 11:21 pm

Daniel Armstrong wrote:
> "Steve Spence" <sspence@green-trust.org> wrote in message
> news:43a417cb$1_2@newsfeed.slurp.net...
>
>
> 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.
>
>

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
http://www.rebelwolf.com/essn.html

meow2222@care2.com

2005-12-20, 12:21 am

Steve Spence wrote:
> Daniel Armstrong wrote:

[color=darkred]
> I have not had anything smoke on our MSW. I'm betting there are good
> MSW's and worse MSW's.

I reckon this is more likely down to the CR PSU rather than invertor.

In a C/R psu the current is limited mostly by the C. On a sine waveform
the CR current is approx sine. On a MSW waveform, the current will be
zero for most of the time, and thus much higher at the waveform V
changes. Since the same total charge is going thru the R over a smaller
time, the much higher peak i will mean much higher peak V across this R
at the same time. Thus the R dissipates several times as much power on
MSW compared to sine.

The ratio of reactance of C and R, the amount of R P_diss headroom, and
the ability or not of the R to handle higher peak powers, will vary
from one CR psu to another. So I think youve just been lucky.

One solution would be to fit a much higher power R

NT

meow2222@care2.com

2005-12-20, 12:21 am

=A312:49 here:
http://www.maplin.co.uk/Module.aspx...343&doy=3D4m12D

NT

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