Another surprise was my desktop computer. Turning
on my screen saver adds an additional 40W load to my
PC’s power supply. Leaving the self-powered speakers on
while the computer is off — a 20W hit. Laser printer on
standby — another 20W. A power strip full of wall
transformers idling away — 25W. Copy machine on stand-by — 20W. As you can see, energy use adds up quickly.
However, unless you’re energy conscious when you
purchase that new video card or rack-mounted power
supply, you might be leaving out an important variable in
your purchase decision: operating cost. Wouldn’t it be
great for manufacturers to list, for example, relative
energy consumption for hard drives?
Just how much extra does it cost to
run one of those 9,600 RPM drives
versus a 10,000 RPM model?
Another area highlighted by my
time with the energy use meter is how
little forethought I’ve given to the
operating cost of the various devices
that I’ve designed and built. For example, in deciding between an inefficient
single-chip linear supply and a more
efficient switched supply, my thoughts
have been on heat production, space
requirements, noise generation,
ancillary component needs, and — of
course — initial cost. I’ve never considered long-term energy consumption to
determine which power supply design
makes the most economic sense.
Here are some examples of
energy design questions that you
might consider in your next project:
•If your project includes a fan, do
you plan to run it constantly or only
•Does the design for your new
device have an auto shutdown feature
so that it shuts down after a preset
time has passed without activity?
•Do you really need a string of
super jumbo LEDs on the front panel
of your new project, or will a small,
energy-efficient LED do the job?
•If your circuit includes a
communications transmitter, is the
power output the minimum needed
for reliable communications?
•If your design includes mechanical linkages and motors (think robot),
and it’s intended for constant use, are
the materials as light as possible? Are
the motors high efficiency or simply
the least expensive to purchase?
Although it’s a good idea to
consider energy efficiency in the
design stage of all of your electronics projects, I’m not
suggesting you double the cost of your next project that’s
going to spend most of its time sitting unused on the shelf.
I’m talking about devices that you plan to use frequently.
As an aside, if you’re thinking of purchasing an energy
meter, go in with a friend or two. Once you know the
energy needs of your equipment and appliances, there isn’t
much need for constant monitoring. And you can always go
with the split power cable if you have a clamp probe for
your ammeter. The point is to get into the habit of using
energy consumption as a factor in your component selection and electronics design decision-making process. NV
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