I was thinking about the 35 volt limit and the fact that the
78xx regulators are linear regulators but for low power needs
what's a power resister and a 78xx regulator going to waste?
DC to DC converters are a lot cheaper than they used to be
and for a heavy load like a laptop I would use something like
that. A "greenish" home with things like LED lighting and
thermoelectric refrigeration could be an interesting use for
a 48 volt DC system in a home. An LCD TV, a surround sound
system and all manner of the electronic gizmos that we can't
live without these days could be adapted to a 48 volt DC
system. I don't remember the part numbers but I remember a
line of controllers made by Linear Technology Corporation
that have input voltages that can range up to 60 volts DC
and provide a constant DC output regardless of the varying
DC input. There are some interesting developments with thermo-
electric air conditioning and I think that a 48 volt DC power
source would be great for that. For someone living off the
grid, a 48 volt system could use 12-2 Romex instead of a large
wire size needed for a 12 volt system to carry the increased
current. I find it an interesting concept.
TDD
You can calculate precisely what a 78xx regulator will waste if you know
the input voltage, output voltage, and the current drawn by the load. As
soon as the input voltage is double the output voltage, you are wasting
just as much power as you are using, and it gets worse as the input
voltage increases.
I don't know how you managed to associate thermoelectric cooling with
"green", because it's anything but. It has its place, but it is
extremely inefficient. Once you go above the size of say a portable
cooler big enough for a 6 pack, a standard phase change refrigeration
system is far more efficient. Look at the size of the heatsink you have
to put on the hot side of a Peltier device. The only reason they are
even used on the portable coolers is to achieve compactness and allow
the thing to heat or cool with a simple polarity switch.
Yes, all these gizmos could be adapted to use 48VDC, but like I said,
the DC-DC converter to do that is very nearly as complex as a switchmode
power supply to convert AC line voltage to whatever DC voltage is
required, and economies of scale make those far cheaper.
As myself and others have stated, there are serious flaws with this
idea, and it is a backwards approach to the problem at hand. Some
portions are viable, such as low voltage LED lighting with a central
battery, I've contemplated something of that nature too, but powering
all manner of battery operated devices from a central source is just not
practical outside of a very small niche.