Mixed voltage house

Does anyone run a mixed voltage house?
12/24VDC for lighting and 120VAC for various appliances?
It seems practical for new construction. Is this a bad idea?

if you have solar thats a great idea

The problem with DC is that you can't run it very far from where you generate it without using large wiring or an inverter to change it to AC. If you can generate DC, run it short distance to battery, then short distance to where it's used, it's great. (Or even skip the battery and use the DC right near where you generate it.)

The great thing about generating yer own power is you can have power even if the light company dies.

My thoughts on DC is to have a wagon with batteries..so that i can move the wagon to the main generator (solar-wind-water-bicycle-propane generator-electric car- rocket stove steam engine-or whatever) charge the battery then move the wagon battery to the point of usage...

Another excellent use for 12V is to have any light switches intended to control high-power devices be on low-current DC circuits, which control relays near the fuse box. Someone in my home town did this, I think in the 1970s.

Much safer over all, and it opens the door to home automation down the road.

I'm certainly no expert on this subject, but there are several recent developments that tend to make separate voltage AC versus DC wiring less useful ...

- all of the high efficiency light bulbs will only operate on AC.  Or put another way, incandescent light bulbs are still inefficient whether fed by 12v or 120v

- DC to AC inverter prices have dropped to the point where a 3500w 12/24vdc to 120vac inverter capable of operating the vast majority of home electrical devices now sells for less than $400.  Overall inverter efficiency now approaches 90% ... thus power losses using an inverter to feed compact flourescent or LED bulbs may be less than power losses using incandescent bulbs without an inverter !

- Copper prices have risen to well over $3 a pound, thus making the investment required to purchase and install a separate DC wiring system much more comparable to the investment required to purchase an AC inverter and skip the separate DC wiring

Many RVs have dual systems - 12v when boondocking on battery power, 110/120 when plugged in. It isn't difficult to manage.

If you are interested in pursuing this idea, I can suggest the Airstream forums, I am sure there are others. Also, many folks who sell photovoltaics are conversant with dual systems.

Remember, LEDs are coming...if your purpose is just to save juice, a dual system might not be worth it. However, if you are off the grid and concerned about back-up system, maybe you do want a 12v lighting system.

When we built our off grid house we put in very heavy wiring coming from the solar controller throughout the house as logically as possible to reduce the lengths of cable needed. It wasn't too expensive and has cut down the amount of energy loss converting DC to AC.

All our lighting is DC and it's easy to find all sorts of low consumption lights for DC. Everyday stuff is all DC like modems, battery chargers, TV, laptop and music. I only use inverters for some things like printers, heavy kitchen mixers, sheep shearing equipment and so on and use the smallest (and usually very cheap) inverter I can for the job.

If your budget is limited - as ours is - spend money on thick cables once and use the power from the photovoltaic panels and batteries as efficiently as possible.

I wired my place with heavy gauge copper for low voltage. I installed high current 12 volt outlets from the main power buss in most of the rooms so I only needed one inverter and could move it from room to room and use it as needed.

the cost and short distance is in the voltage, not the AC or DC, if you run 12 volt AC or DC you will need a lot larger wire  then if you run the system at 120 volts,

example 100 watts at 12 volts, will take, 8.3 amps to operate,
the same 100 watts at 120 volts will take .83 amps to operate,  it will take a lot lot heaver wire to carry the 12 volts than the 120, and to keep the voltage drop from becoming excessive you will either have to keep your distances short or larger wires, to carry the amps.

Some countries use DC on some of the very large transmission lines, as the losses on DC in that type of situation are less, ( they are found mostly in Europe).
http://en.wikipedia.org/wiki/High-voltage_direct_current

http://www.highvoltageinfo.com/2007/08/dc-high-voltage-transmission-lines.html

Cool... seems the info i read in the 70's was wrong or i read it wrong.

Ronie 
in practice your statement is most likely in the 98% true,  as most systems that use DC us a 12 volt plan, and a 120 volts AC,

so the reality of your statement is that you will need heavy shorter distances by using a DC system, (not that it is DC but because it is 12 volt),  and one could run longer distances by using AC as most would at least use 120 volt inverter to step up the voltage  so the runs could be smaller and longer if needed with out much loss.

If one set up a 120 volt system, 10 12 volt batteries or 20 6 volt  and could use 120 volt DC or 120 volt AC,  there would not be any difference in the wire size or distance one could run the losses (as far as were concerned) would be inverter losses.

distances are mostly governed by voltage drop,  and on the lower voltages (12 volt)  the less drop one can afford,   If you have a 5% drop in 12 volt you are 11.4 volts, (depending on the type of equipment one is running  it could read the battery as dead, at that 11.4 volts, as a dead battery would be considered at 11.9 by hydrometer reading, of 1.120 Specific Gravity http://www.batterystuff.com/tutorial_battery.html  the good side is most battery put out over 12 volts some, but if your inverter is some distance away from the battery bank it could end up reading the bank as dead and shutting down  when the bank was still had plenty of reserve, in it,
on the 120 volt side if you have 5% drop you would get 114 volts which is still with in most items design parameters for operation,

the problem is you have 12 volt RV items that one can use, and you have 120 volt grid products one can use,  so your basically stuck with the 12 volt DC, or the 120 volt AC choice,

the remaining products of the 32 DC volt wind charger products of the 1930 and 1940 are few and far between,

Right now I'm using a laptop off 12 DC and the modem on the 120 AV  side. 12 volt is more efficient for some things like lighting  while other thing 120 is better.

Glad to get the info from everyone... I have yet to decide what to do about the grid and power at my country land.. I have no zoning and no restrictions there so i can do whatever i think is best.

I hate having monthly bills , but from my research (30 year old research) it always said that it was cheaper to hook to the grid if it was nearby. The grid runs on my place.....But IF one can NOT need a lot of electricity, then the grid might be more expensive in the long run.
And a monthly bill no matter how little i use.

I have desiring a wind turbine for the last 30 years, cost or cash,  has been the major factor where I have failed in the plan, (as in most instances one can hardly get a loan on that type of investment, (or at least from my bank),

what I have seen, if I would do the figures and and look at current costs, it will never compared, with the current rate.  (the same with a water pumping windmill), when compared to the grid,

but If I would have bought the tribune 30 years ago it would have payed handsomely in the last 15 years,  when I studied it out 15 years ago it would be making lower cost power now, (under the constraints of no major problems and repairs), ( and it produced as advertised),

and I conclude if I would bite the bullet now and put it in most likely with inflation in 10 or less years the cost would match again and start to break even or pay in savings,

do I have a turbine up yet NO, currently I am exploring the grid tie systems, and saving on the batteries as the grid in our area has been very reliable for us, only one major outage since the REA put in lines in the late 1940's early 1950's, 

I am in a excellent wind region tho,

If you have excellent wind and good location, some wind/electric investors may put up wind generators on your place and pay you every month for the place to put their wind generators.

I missed out on a cell tower by a few feet.. my neighbor across the road gets $1000.00 a month for 30 years as rent for a cingular cell tower.

currently I have leased the ground to a company for commercial wind tribune consideration,
but the hang up seems to be getting the potential power that would be produced out of the area,  the transmission lines are the big hangup on the commercial power end, (at least in our area), this same company on the opposite side of the river valley they built two wind farms,  but the transmission line on those farms are using all the capacity it has, so hooking on to it is not a possibility is what they say.

A mixed voltage cabin was precisely what I envisioned when I began the planning stages for our cabin in the woods. I was thinking 12 VDC for lighting and 120 VAC for things like the microwave, power tools, toaster once in a while, blender, stereo...

Over time as the cabin plan grew from 12 x 20 to 15.75 x 30 feet I hung onto that idea. It simply seemed to make a lot of sense for the lights to use DC directly from the batteries with no inverter losses.

In the end I switched gears and built the cabin with 120 VAC as the prime power and a 12/24 VDC sub system for the RV type water pump and a ceiling fan.

My reasoning involved several things. The split system as originally thought of used more $$ worth of copper wiring than the finished product, because of the above mentioned current issues. The original plan required special plugs and receptacles for a couple of converted table and floor lamps in order to prevent accidentally plugging a 12 VDC lamp into a 120 VAC receptacle and vice versa. I was certain I could keep things sorted out but was less sure of others who might be using the cabin from time to time.

Wall switches that are capable of being used for DC current are almost non existent. At least ones that are approved for residential use are uncommon. Using a standard home light switch on a DC circuit will result in a quickly burned out switch.  An side comment here... this would also be a problem with using a higher voltage DC system; DC rated switches must have much larger and expensive contacts.

Building a 120 VAC system also eliminated the need to search for sometimes hard to find DC devices. We use the same stereo, same DVD player, same TV, same blender, etc as we have at the city home. These AC appliances also cost less than most DC items I found as well as there being a deeper inventory to choose from. We use common 120 VAC Edison base CFL's for lights; no need to buy special lamps or fixtures.

Also, there is no need to explain how things work, what one must do if they want to use the microwave for a few minutes. Just turn it on and go.

I built the PV system based on a 24 VDC battery system. The inverter selected supplies pure sine wave power as devices like motors run cooler and use less power than when run on square wave inverter power. The inverter chosen also has a search mode so when no power is being used the inverter is silent. In silent or standby it uses a few milliamperes of power, less than the natural self discharge of a lead acid battery. The 3500 watt inverter supplies all the AC power we would ever use at one time. If we need more, to run tools or whatever, there is always the generator.

While I have no plans to ever sell the mountain property I also think it would be easier to sell a more conventional AC based cabin than one with AC and DC mixed throughout.

So sure I believe one could build a split system, many have done so. But for me what I described is a better fit. Others will find their own version of perfection in something else, perhaps a DC only system.