My review on P3 International P4400 wattmeter
AC/DCdude17
by P3 International. It has quite a few functions and I'd like to
call it a consumer grade "quasi power analyzer". Before making this
purchase, I have tried EED's "watt's up?". I returned Watt's Up?
As Kill-A-Watt proves to be better value for my need based on Dave
Houston's review and information from elsewhere on the
Internet.
My reflections on this product;
Claimed accuracy: 0.2%. No further information available.
Resolutions;
V: 0.1V
A: 0.01A
Power: 1W
VA: 1VA
KWh: 0.01kWh
Time: 1min up to 99:59. 1hr from 100hrs
PF: 0.01
Good:
This meter will measure of course watts in addition to Volt-Ampere,
instantaneous line voltage, line current (supposedly true RMS),
power factor, line frequency. The product has a built in timer and it
can display the cumulative kWh and elapsed time. Definitely a
Kick for $50. It is very easy to use. You plug it in and it hit the
button to change display and simply read it.
Not so happy about:
Although this product has the function of a low-end laboratory grade
power analyzer, its accuracy is very questionable. A properly
written specification data for digital measurement instruments will
define many factors thoroughly which this meter lacks. (Example:
Accuracy on power +/- 0.5%+4 counts for DC to 4KHz at load greater than
20% of full scale and crest factor below 6) All you see
is "0.2% accuracy" on the package. This is a wishful thinking on
manufacture IMHO. The accuracy figure is suspicious enough and
there is a very good chance it doesn't measure a lot of linear loads
properly. I have verified personally that it doesn't measure
half-wave rectified load accurately at all. (verified by measuring
smoothed DC current and voltage at output using known meter or
mathematically if outcome is known). I don't expect better than +/- 5%
from this meter on non-sinusoidal load such as dimmed lamp,
half wave rectified load(overhead projectors and bi-level dimmer/speed
control for example), computers and anything else with a lot
of harmonics.
Fails to add up. When you individually measure two loads, it may
appear as 3W and 58W. When you plug them together, it doesn't
necessarily add up to 61W. I believe this is due to the fact it isn't
measuring the 3W load accurately by itself. This meter lacks
resolution and low-range accuracy for proper measurement of phantom
loads.
Response is relatively slow. It is slower than Watt's up and the
response time until a reasonable result is displayed is one to
two second.
kWh count is lost when power is lost, even for a very short period
of time.
There is about a 5-10sec delay after plug in before it starts
measuring.
YOU CAN NOT use it on a generator or inverter. My package had a sticker
that said "not for use with generator or inverter". P4400
gets it's own power from the line through an RC(resistor and capacitor
in series) circuit. When you put it on inverter power, the
resistor gets EXTREMELY HOT, which indicates excessive current
condition. My meter wasn't destroyed by this, but it can't be
good for it. On the other hand, EED's Watt's Up? is built with more
stable power source and it is fed by step down transformer.
Watt's up doesn't seem to have any problem on my inverter.
Dave Houston
In my review, I noted that the wattmeter truncates values rather than
rounding them. Thus, a reading of 03W may be anything between 3W and 3.99W
and the 58W reading may be anything between 58W and 58.99W. So, a 10W
reading could be off by 10% and a 01W could be off by 100%. My review noted
that the low load wattage readings were not accurate, saying you would have
to use the KWH function over some period of time to get a more accurate
reading of low level loads.
http://www.laser.com/dhouston/killwatt.htm
I'm not surprised that your 3W + 58W loads did not add up; I am surprised
that you expected them to add up.
Phantom loads can only be measured using the KWH function over many hours.
The lower the load, the longer the time period required for accuracy. That
should have been clear from my review.
I exchanged e-mail with P3 and was told that the 0.2% accuracy figure quoted
is for voltage and current measurements. Other values are calculated from
those and overall accuracy for calculated results is 0.4% at best. Factor in
the truncated values and overall accuracy suffers still more.
However, my own tests using a 3-way 50/100/150W bulb gave consistent
readings for each element and the sums.
For low level linear loads, I also found that independent measurements of
current and voltage made with my DMM (consumer, not laboratory grade)
confirmed the low level KWH readings taken over tens of hours were
reasonably accurate at about 10%. The disparity could be in the P4400, my
DMM, or a bit of both. I'm happy with 10% accuracy at 3W.
I don't believe your test using a half-wave rectified signal is valid.
The P4400 only samples at 2048Hz. That may not be enough to get an accurate
measurement of the waveform from your inverter. Again, I have to express
surprise at your surprise that it doesn't work with your inverter given the
sticker on the package.
While I think the 2048Hz sampling rate is probably too low to get a precise
measurement of non-linear loads, 5% accuracy (your figure, not mine) on low
level non-linear loads is beyond the capability of several metering systems
costing far more.
That said, even at the P4400's low price, it will take most people years to
save enough in utility charges to pay back the $50 cost.
BTW, how did your system for Home Automation via DTMF turn out?
AC/DCdude17 <Je...@prontoREMOVETHISmail.com> wrote:
Dave Houston
It's been awhile since I checked on who sells the P4400. It's now available
from RadioShack (63-1152) for $49.99. It's also available from a couple of
sources for about $10 less than what I paid for mine.
http://www.etaengineering.com/killwatt.html $40
http://www.coblex.com/product.asp?productid=276 $39
dhou...@fuse.net (Dave Houston) wrote:
William P.N. Smith
> http://www.etaengineering.com/killwatt.html $40
>>That said, even at the P4400's low price, it will take most people years to
>>save enough in utility charges to pay back the $50 cost.
I dunno, I'm trying to get a handle on a $300/month electric bill, and
I could probably pay the thing back pretty quickly.
I'm starting by reading the electric meter at 6AM every morning, just
to see if I'm using a lot every day or if it's the A/C or hot tub or
computers or what that's causing problems.
Will a clamp-on ammeter and a search thru the breakers get me
anywhere?
Dave Houston
In the case of a $300 bill, it might help a lot but it is limited to
something like 1800W and will only work with plug-in 120V loads. It's also
dropped in price by $10 so the payback is a bit faster.
What I really meant was it wouldn't pay for itself by finding and letting
you eliminate phantom loads.
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http://www.laser.com/dhouston/bx24-pcb.htm
Dave Houston
Here are a few URLs that might help. I'm not sure they are all current.
http://www.brandelectronics.com/powermeter.htm
http://www.epd.com/power_meters.html
http://www.brultech.com/
http://www.amplepower.com/products/emon2/
http://www.sbt.siemens.com/press/apogee_pr3.htm
http://www.energymonitor.com/features.htm
http://www.seanadams.com/pge
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http://www.laser.com/dhouston/bx24-pcb.htm