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Google's new grid "green meter" service.

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Posted by vaughn on February 11, 2009, 4:43 pm
"The new service from Google is called PowerMeter and it's free to both home
and commercial users.  While this sounds great, there's one significant
catch -- PowerMeter relies on others to provide the information it needs.
Google is hoping that makers of home electronics and appliances will add
hardware which will feed the service information wirelessly.  It also needs
utilities to provide it with grid metrics."

Complete article at:

Or (naturally) just Google for more information...

I haven't had time to fully absorb this yet, but I am starting to become as
wary of Google as we all have become of Microsoft.  Google is becoming ever
bigger and ever more powerful, and the monster feeds itself by sticking its
information-absorbing probe further and further into our lives.


Posted by Jim Wilkins on February 11, 2009, 9:01 pm

I was searching for cheap USB data loggers and remembered that I still
have an old Radio Shack multimeter with a serial port, model 22-805.
The serial port appears to be optically isolated from the meter
although the manual says nothing about common-mode voltage, only
1000VDC, 750VAC maximum.

Unfortunately RS discontinued it. I believe it was a previous model of

A data-logging current meter like this can complement the Kill-A-Watt
by recording time-stamped useage patterns and the variable current of
washing machines etc. It could monitor the operation of a 240V water
heater by placing a current transformer around one lead and recording
the milliamp output. The clamp-on AC current probe for my Fluke meter
puts out 1mA between the banana plugs for each Amp in the wire through
the jaws. The meter reads 16.4mA for my water heater, agreeing with
the 16A shown by the Amprobe. Of course it doesn't measure phase shift
and unlike the KAW can't distinguish between real, metered current and
reactive current, but a water heater draws metered current.

The included software updates no faster than once a second. It was
easy to write a program that records as fast as the meter samples,
around 5 times a second. I plan to make a universal battery charger
controlled by voltage and current DACs driven from the printer port
with this meter reading back the battery voltage.

This is the low-cost data logger I had originally considered:
I could prototype a clamp-on remote current meter using it but I'm not
nearly qualified to design a safe, approved commercial one.

Jim Wilkins

Posted by Tim Jackson on February 11, 2009, 10:22 pm
 Jim Wilkins wrote:

One problem with designing a clip-on ammeter as a commercial domestic
product is that the clamp has to go around only one leg of the supply.
Approved domestic equipment uses sheathed cable where the legs cannot
safely be separated by the user. (In the legal, not getting sued, sense
of 'safely'.)  You could only really sell it for use on the meter tails
of the incoming supply.

Tim Jackson

Posted by Jim Wilkins on February 11, 2009, 11:57 pm
I picked up two large current transformers to do just that, then
realized that interpreting the measurements could be too confusing.
For instance all 60W light bulbs change the reading the same amount, I
wouldn't know which ones were left on. The really high short-term
demands like the oven, clothes dryer or welding are obvious, just read
the meter before and after. Arc welding BTW uses surprisingly little,
one or two KWH a day, because I spend most of the time on cutting,
fitting and cleanup.

It made more sense to measure the power for each device with an
Amprobe or KAW and then watch for unnecessary use of the larger ones,
or decide to swap them for more efficient ones.

The biggest savings came from shutting off the full-sized refrigerator
and learning to live with a small one. That saved $0 a month. Same
for a freezer, can you recover its $0 a month operating cost with
large food purchases?

Whatever the electrical measurements show, the only possible decisions
are about changing habits or appliances.

Jim Wilkins

Posted by Tim Jackson on February 12, 2009, 10:44 am
 Jim Wilkins wrote:

I'm not sure how much we need to measure current anyway. We *know* how
much current a 60W light bulb draws, it's 260mA here. With
self-controlled (eg thermostatic) devices, it's usually just a matter of
measuring on-time (at the thermostat - of course that's easier said than
done too) to get a handle on how much power it is using, plus maybe a
one-off current measurement (eg via an adapted extension lead) if the
rating plate isn't as clear or honest as it might be.

I wonder if there might be a market for a battery powered
light-activated hours-meter, that could tell you how long a particular
light bulb was switched on, just by sitting next to it.


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