[LINK] Australian energy efficiency standards for personalcomputers and monitors

[Glen Turner]

On Tue, 2007-10-16 at 15:47 +1000, Pilcher, Fred wrote:
> Not strictly in the spirit of the thread, but I've always felt that one
> of the major power wasters is the plethora of transformers that I need
> to keep plugged in. I haven't counted, but I'd say that I probably have
> ten running at any given time, whereas if all my devices had the same
> power requirements, one would probably do.

Hi Fred,

Large transformers running with a light load are less efficient than
small transformers running at full load.  So the argument is one of
reduced capital costs and increased convenience.

Worse, almost all large transformers are currently much less efficient
than they should be. Small transformers are generally kept efficient
because they drive small devices and thus need to use the more efficient
and smaller modern transformer designs.

The 80 Plus campaign in the US hopes to improve the design of the
large power supplies used in computers. But even that has 20% of
the arriving energy leaving the power supply as heat (that is,
about 80W of waste).


The second problem is that direct current has higher cable losses than
alternating current. We've all familiar with the household 10A flex,
this carries 2400W of energy. A DC cable carrying 2400W is roughly
three times the diameter -- that is, about nine times the copper.

So the notion of cabling the house for DC runs into trouble. I've
done that to avoid DC-AC conversion losses, but my calculation is
that for about triple the cable cost I end up only saving about 10%.
Simply using a 10% larger solar system would have been cheaper, and
would have avoided a lot of motor redesign.


There is one popular case we could make work well, and that's devices
with rechargable batteries.  They needn't have long cables, since the
device can be bought to the power source.  But before we see solar
designs giving a few recharging points we need -- as you suggested --
a common charging connector.

It's possible that USB could end up as that connector.  But USB is
really only designed to power low current devices.  There is a
Powered USB specification, but it's unlikely to be commercially
acceptable due to its poor design.

Best wishes, Glen

-- 
 Glen Turner