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Anyone make a current/voltage watt-hour meter with RS-232 output? - Page 2

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Posted by Guido on April 8, 2010, 2:04 am

Sum Guy wrote:

I don't know about that. I was going to ask why you wanted a data logger
that didn't log, but thought you might of wanted something to repair.

Posted by Sum Guy on April 8, 2010, 2:22 am

Guido wrote:

How exactly are you interpreting the last paragraph of my original post:

Do any modules or devices exist where I can attach a couple of coils to
measure current on my 2 hot leads and three wire connections to measure
my 2-phase 220 VAC service, and generates numeric data I can read via
serial interface by a PC with a time resolution of my choosing?


Wasn't it clear in that paragraph that the PC was going to be doing the
logging, and obtaining the data from a measuring device connected to my
power mains?  

Wasn't it clear that I was looking for a measuring device or module that
itself does not have logging capability - because the PC was going to be
doing the logging?

Is english not the primary language spoken by the readers of these news

Posted by Jim Wilkins on April 11, 2010, 1:19 pm

Stop complaining, free advice is worth what you paid for it.

Current sensors on the breaker box input don't tell you what's using
the power. That was my first try but the only practical improvements
are reducing usage or replacing individual loads.

If you rephrase the question into what each appliance consumes the
answer is simpler and cheaper. A Kill A Watt gives instantaneous and
integrated consumption for 120V loads, the Radio Shack clamp-on meter
and a PC for hard-wired 240V ones like my water heater. Heater
elements draw true power so the current it measures is the current
billed. The KAW shows apparent power (VA) as well.

Unless your line voltage fluctuates the only reason for measuring the
voltage is to compare the phase angle between voltage and current,
which you may find difficult with a serial-port meter and PC internal

Once you know the power drawn you only need to track the times of

It's a little more complex for variable-demand devices like an air
conditioner but a KAW is enough to show that for instance running it
at night is more efficient than during the day when outdoor air is
hotter. For that you need to log air temperatures as well to show -
why- the electricity was consumed.

I use an old laptop minus the dead battery for logging because it
draws only 14W, my lowest-power desktop takes 35W. If that seems
trivial my entire year-round demand averages less than 180W.


Posted by news on April 7, 2010, 1:48 pm

The simplest device to install is likely to  be one that has its own
dispay and/or datalogger, as there are several units which can monitor
the power factor as well as the volts/amps.

If you're electrically and electronically qualified, you could order
current transformers for the amps, devise voltmeters for the volts,
and use a PICAXE microprocessor ( http://www.rev-ed.co.uk/picaxe/  ) to
computer the watts - but you would still need to determine the
reactive component (power factor) of the load.

The units that mount in the breaker box and send data to a remote
display via powerline carrier will probably interfere with any X10 or
similar power control devices that you may use.

If your power provider uses electronic metering, then you might be
able to monitor the KWH by counting pulses from an LED on the face of
the meter.  This is usually very easy to do, but varies by type of
meter (my power provider uses Landis & Gyr meters whch do not have the
pulsing LED).  If you meter has the LED, then check the projects in
the PICAXE forum for something that you can use or adapt:


Posted by Gene S. Berkowitz on April 11, 2010, 3:40 am

Check out Brand Power Meters at:

These can be used to measure a single appliance, like a Kill-a-
watt, and they offer a clamp-on current transducer for whole-
house monitoring. They will customize to your needs for a
reasonable price.


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