Hi Adam,

Wow, what an interesting and ambitious idea! I think you could make it
work, but there are some problems you would have to contend with.

#1) Inefficiency. A typical 120V circuit in a house can handle 14 amps
and uses 14 AWG wire. If you used 12V instead, you would need to handle
140 amps (assuming you wanted to be able to deliver the same abount of
power). Using the same wire, this would result in 100 times the resistive
losses (because power loss in a wire is equal to I^2*R). You would need
to increase wire size to 10 times the diameter (about an inch thich, REALLY
huge
wire) to get the losses down to the same level as a typical 120V circuit
(on the order of 100 watts loss at full load).
If you have very few appliances which need hundreds of watts, then you
might get away with making only one circuit with such high power, and
keeping that at 120V.

#2) Running standard appliances. How are you going to get a
refridgerator, hair dryer, washing machine, clothes dryer, etc., which
run on 12V? If you use huge inverters to run these, a lot of your
advantages are probably lost already.

#3) Running computers. You mention that it would be easier to run
computers from a 12V supply line. That is not necessarily true. The only
reason why the 120V switchers are rather poor is that they are designed
and built to be cheap. If you are going to use high quality DC-DC
converters, you probably could do just as well with a higher quality 120V
swiching supply.

#4) Converting from 120V to 12V efficiently (unless you generate it all
yourself). It would take a REALLY huge transformer to supply the levels
of 12V we are talking about. A switcher to do this would be bigger than
anything commonly available, AFAIK. You might consider using 12V AC
(probably 12V rms, not peak) for your supply to make it easier to use
transformers at places where higher voltages are needed.

I know I have been very negative in what I said above, but I just wanted
to point out a few problems with doing this in general. I think your idea
has some merit, but I think you should probably still have at least one
120V )or maybe even 240V ) circuit which you can use to run a few
appliances which draw large amounts of power. Then, you could supply the
rest of your house with 12V, to run your low-power LED lighting and small
electronics projects.

Please let us know if you try this!

Sean



On Sat, 14 Jul 2001, Ghetto Scientist wrote:

> For sometime I've been thinking about the merits of wiring a house with a
> low voltage bus (12 volts).
>
> There are a number of reasons I think this could be beneficial.  First I
> really don't like the switching power supplies in PCs.  They are noisy not to
> mention the fact that they seem to go bad on a semi-regular basis and when you
> put a few of them in one room they generate a nontrivial amount of heat.  If
> I wired my house for 12 volts I could run a PCs off a simple voltage
> regulator / DC-DC converter.  Another benefit would be small power supplies for
> embedded systems (home automation components) are much smaller when the primary is
> only 12 volts as apposed to 110 volts.   Once white LEDs come down in price
> they could replace the [hot, inefficient] incandescent lights currently in
> use.  Also I could build a big UPS for all low voltage items in my house.
>
> Another reason I am interested in low voltage home systems is I have often
> though of living "off the [power] grid".  12 volt systems would largely
> eliminate the need for expensive power inverters.
>
> What I am wondering is what would be the best (most efficient) method of
> stepping down enough power from line voltage to 12 volts?  Would a "simple" wire
> wound transformer due?   Maybe a switching power supply.
>
> Sorry for the odd questions, I know next to nothing about power conversion.
>
> --adam
>

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