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Check power consumption, costs, greenhouse
gas emissions and more . . .
How
MUCH POWER
are your
appliances using?
Despite international efforts to reduce the
standby power requirements of appliances,
this modern phenomenon continues to be a
real problem. Virtually every mains-powered
device is now in on the act, or soon will be.
Standby power increases your energy bill
and adds to the greenhouse effect.
By PETER SMITH
T
V SETS, STEREOS, VCRs and
the like have long relied on
standby power. More recently,
“convenience” electronics have been
grafted into up-market household
items such as dishwashers, coffee makers, cordless telephones and washing
machines, all of which are designed
to be permanently powered.
Don’t think that these devices use
much power when “off”? Well, you
might be surprised to discover that
10-15% of all household power is consumed by devices in “standby” mode.
According to a 2001 study by “Choice”
magazine, appliances not performing
their main task drew a constant total
of 87W, on average.
That works out to 760kWh in a year,
for a cost of almost $100. And standby
power consumption certainly hasn’t
76 Silicon Chip
decreased since then.
Consider the 100 million homes
in the United States, for example.
In total, they consume roughly 5GW
of standby power. According to one
source, this equates to about 8GW after distribution losses and generation
reserves, or about the output of eight
power plants. And that’s just for the
domestic sector!
With this in mind, you may wish
to save some money and the environment by switching off appliances at
the power point when not in use. Of
course, it’s simply not practical to
power off all devices. For example,
microwave ovens and VCRs include
a real-time clock that would need to
be programmed at every power up,
while cordless phones need to be on
all the time. However, other devices
such as PCs and their peripherals can
be switched off.
Measuring power usage
Before you can make informed decisions about power usage, it’s necessary
to know how much each device consumes, both during normal operation
and in standby mode. Typically, the
power rating printed on the label of
a product indicates maximum input
only, accounting for things like surge
current at power up, motor start, etc.
Real power usage is likely to be quite
different.
How you use an appliance will also
have a major impact. For example, if
you normally run your fridge in the
middle of its temperature range, it will
obviously consume less average power
than on the cooler settings.
The answer is to connect each device in turn to an electronic power
meter. That way, you can determine
the average power consumption, in
line with actual usage. To help with
this, a South Australian company,
Computer Control Instrumentation,
has come up with a great little handheld meter called the “Power-Mate”.
It can measure instantaneous power
use, accumulated energy consumption
and more.
Power-Mate, mate
The Power-Mate is supplied in a 150
siliconchip.com.au
Special Offer
Table 1: Power-Mate Specifications
Measurement/Calculation
Range
Watts
0 - 2500W
Volts
170- 270V RMS
Amps
0.000 - 10.000A RMS
Cost & cost per hour
0 - 99.9999 ($)
Cost per quarter & year
0 - 9999.99 ($)
Energy
0 - 999.999 kWh
Greenhouse gas
0 - 999.999 kg
Run time (max).
99 hrs, 59 mins, 59 secs
Basic accuracy: better than 1% for all measurements
x 80 x 30mm plastic case. It features
a bright red 7-segment display and
includes a four-button tactile keypad.
A 1-metre cable exits from the case, terminated in a combination mains plug
and “piggyback” style socket.
Hooking up an appliance for testing
couldn’t be easier. The Power-Mate
plug goes into the mains outlet first
and the appliance simply plugs in on
top. Maaaate!
In all, seven primary measurements
and calculations can be displayed.
Repeatedly pressing the “Mode” button cycles through each of the possibilities, as well as the “Setup” and
“Clear” functions that we’ll come back
to shortly.
There are also 15 additional display
functions, accessed by pressing one
of the other three colour-coded keys,
labelled “Enter”, “+” and “-”. It’s easy
to determine what information is available in a particular mode by referring
to the matching colour-coded table
below the keypad.
Measurements include line voltage (volts), current drain (amps) and
the power consumed (watts), all in
real time. A simple press of the “+”
or “-” buttons momentarily displays
the maximum or minimum readings taken since power on. These
measurements would be handy for
service technicians, who often need
to measure things like start-up and
surge currents.
The real power of this unit (pun
intended) is to be found in its energy
consumption and cost calculation
functions. At power up, the PowerMate immediately begins to show the
accumulated energy used by the appliance in kWh units; this is the default
display in “Energy” mode.
You can also see the projected
hourly energy usage based on measurements thus far by pressing the “Enter”
button. Pressing the “-” and “+” buttons extrapolates the measurements
over quarterly and yearly periods,
respectively.
Hit the “Mode” button again and
you can immediately see how much
it’s costing you to run the appliance.
Once again, you can have the option
of displaying current, hourly, quarter
or yearly costs. It surely doesn’t get
The Power-Mate is designed,
manufactured and approved for
use in Australia. It is available
from the Alternative Technology
Association, on the web at www.
ata.org.au or phone (03) 9419
2440. Currently, the unit is priced
at $346 plus GST in one-off quantities, which includes a 12-month
warranty.
Computer Control Instrumentation is making 25 units available
to SILICON CHIP readers at the
special price of $315 plus GST.
To take advantage of this special
offer, e-mail Mike Russ at mike<at>
c-c-i.com.au or write to PO Box
195, Goodwood, SA 5034.
Note that only bank cheques,
money orders or bank transfers will
be accepted for this offer.
any easier than this!
For the environmentally conscious,
the unit also calculates the equivalent
amount of greenhouse gas liberated,
based on the ratio of energy consumed
to a constant. By default, this is calculated at 1.2kg of CO2 per kWh, which
is the accepted value for fossil-fuelled
electricity generators.
Both the cost of electricity per
kWh units and the constant used for
greenhouse gas calculations can be
programmed in “Setup” mode. Entered values are retained in memory
at power off.
Finally, a “Clear” function allows
you to reset the accumulated values
of time, energy, cost and greenhouse
gas emissions without having to turn
SC
the unit off.
COMING NEXT MONTH
How Many Watts?
For those who prefer to build their own, watch out for
our Energy Meter in next month’s issue. It features a
multi-function digital readout that will tell you energy
usage, actual power cost and much more for the various appliances in your home. It’s easy to build and is
based on a PIC microcontroller.
78 Silicon Chip
PROTOTYPE SHOWN
siliconchip.com.au
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