DC Low Voltage Whole House Systems?

There was a group in the late 80's who advocated a dual wiring scheme for residential electricity. The high-voltage, high-current AC system would continue to be installed along with a low-voltage DC system.

The DC system would have a large "master" transformer feeding multi-tap RJ-11 or RJ-45 outlets to power electronic gear.

The thinking was that every piece of electronic equipment has a relatively inefficient transformer or wall-wart that wastes quite a bit of power. A master whole-house transformer would be a much more efficient way to distribute that power. Also, DC is more efficient as a distribution medium over short runs.

Has anyone heard of any further developments on this issue? Seemed like a good idea at the time.

 

One would think that the large "master " converter would have more loss than a couple of wall warts. Not to mention the added heat produced by one that the a/c unit would have to compensate for.

 

First problem is that not all electronics uses the same voltage. Second problem is that low voltage distribution, even within a house, is very inefficient. I don't think this is a good idea. I don't even think low voltage lighting is a good idea.

 

First off how bad are those little wall warts vs a large master xformer? I also don't remeber enough of my transmission line theory but I would say that transmitting household AC current is not that inefficent. At only 60 hz I would imagine that a wire looks more or less like a resitive load. OK at long lengths other factors com into play but still. Would you rather pump 120v AC @ 1amp through 14 gauge wire for 50 feet, or 10 times the current at 12V DC over the 22 gauge wire used for RJ-11/45? I'd think the voltage drop alone on the DC would make up any wall wart lose.

Lets not even get into the extra wiring cost, or the retro fit of old house.

Cute Idea but I imagine it will never be seen.

 

I'm going on memory here, but I believe they claimed that a whole-house system would be 95% efficient including line loss versus the maximum 80% efficiency of cheap wall warts and internal xformers.

The multiple lines in the RJ plugs would carry several common voltages (24, 12, 5 ...).

Still, I realize that the cost would far outweigh the advantages. In addition, since not everyone would have the low-voltage system, consumer electronics devices would have to provide both a transformer and a bypass/tap.

Hey, it was a good thought...

I'm waiting for fusion reactors so I can disconnect from the grid and use my coffee grounds for fuel.

 

With LED lighting, rechargeable battery appliances and variable-speed DC motors for heating/air circulation systems becoming increasingly common, does it make sense to build DC wiring into new house construction in parallel with AC wiring? Are the RJ11/45 wiring and plugs sufficient to handle area LED lighting?

 

Voltage drop on LVDC I think is the main issue. Imagine #6 Cat 5 for the RJx jacks.

 

Wow. RickJ6956 was my uname when I first joined this site in 2002, and this is one of my threads.

Funny thing is, 6 years later, most of the devices in my home are now low voltage. They run on wall warts instead of a master power supply.

All of the gear in the commercial installed systems I've done in the past few years could use a single 20-amp DC 12/24 volt power supply.

Cat 5 or 6 can realistically handle up to a couple of amps. With the exception of audio power amplifiers, projectors, and TVs there is surprisingly low current draw in the other devices.

 

I think Ray (and others) hit the nail on the head. Voltage drop is the killer.

At 120v, you can run 1800w of devices on 14ga wire all the way across the house without even giving it another thought. Even if you were talking about high efficiency LED lights, you'd have to run much higher guage wiring to make it across the house... or even into the next room.

I'm not even sure you can get one LED to light up over 100' of 22ga wire...

Another poster here was installing 50w LED lights. The manufacturer recommended 10ga wire for 5', 6 ga for over 15 feet, and it just kept going up from there.


Certain industries do this though for very small areas. Telcos for example have a single large transformer bank, then distribute out 48v or 24v through their gear, but all contained in a rather claustrophobic room.

 

It seems as though it could be practical if we switched to a DC bus with taps type of design that ran throughout the house rather than the star design we use for A/C circuits.

I'm not really sure it would be any more fruitful than just continuing development of efficient higher voltage LEDs connected directly to the A/C line. Really the "best" system would be a single 240V 15A circuit that powered all of the LED lighting in the entire home with one #14 cable. You get low materials usage, high efficiency, low voltage drop, etc. Perhaps even couple that with a code change to allow #16 or #18 for LED lighting taps to really cut down on materials.

 

Hmm maybe the pocos could start offering a 220 with grounded conductor as an option. You could have both available and as more and more products designed for use in countries that use 220v residential circuits were bought in the US the 120/240 would be phased out.

 

I have a 500 foot box of number 18 fire alarm cable at home, I will connect an LED module to it and a 12 volt battery and see what happens tonight.


Common telephone systems use 48 volts DC and operate over several miles radius from the central office.

 

The problem I see is convincing every manufacturer in the world to make there stuff run on " X " volts dc. That is far from standardized right now.

........and since this thread is 6 years old...apparently the idea hasn't caught on yet!

 

I was trying to convince some folks at work that a centralized rectifier and a 48v DC bus made sense in our server rooms, but no bite yet, and we have a huge amount of gear that can actually run on 48v DC power, almost all network/server equipment have a DC power supply option for TELCO deployments. I don't see it gaining much ground in the consumer space though. It does seem like it would make more sense for an OFF GRID type of installation where you are going to have a DC power source that is inverted to AC rather than going the other way around :-/.

Something else that looked interesting (off topic) was 440v 3phase, meaning L-N 220, vastly simplifying the PDU (and thus making it thinner).

 

Not always the case with 480 ( 440 ) volts system there are quite few diffrent verison of connection depending if that is single phase or tri phase supply and grounded or ungrounded delta system or wye system

This kinda info useally out of the DIY scope but I know few may have some experince with it but most electrician in this forum are pretty well versed myself I am master electrician and work anything from basic home set up to complex industrail electrical system which they have much more than 480 volts avabile

{ I know couple electricians in this forum three of them I know for sure they are commercal / resdentail electrician but others not for sure I will ask them later }


Merci,Marc

 

Even if the voltage dropped down to 5 volts, the LEDs would still turn on due to the low turn on voltage for most of them.

I see it quite a bit on industrial control panels where induced voltages from nearby wires can cause an LED to come on dim (but still bright enough to see) even when the power source to the LED is off.

 

Also Luna being an engineer I'm sure you remember why the original test of a trans-Atlantic cable failed and won' duplicate that experiment.

 

Voltage drop is a result of load on the wires and the resistance of the wire. That 500 feet of 18/2 will run a single (typical 20ma) LED at 5vdc over that distance. I've run 3vdc and 5vdc IR emitters well over 300 feet on Cat5 to control devices and have never had a problem. Heck, Cat5 itself holds its spec to 100 meters, and the voltage that carries data to that distance is just under 3 volts.

If the voltage drop is too great -- and the wires will handle the amp load -- just step up the voltage so you get what you need at the other end.

As for the various voltages required of a whole-house DC system, it's not a big deal to use either a multi-tap transformer, divider networks, or several v-regs. Manufacturers have standardized somewhat to 6, 9, 12, 18, 24 and 28 volts DC. The highest wattage devices also require the highest voltages.

We're used to pulling home-runs to a central location for ethernet and TV cabling, so why not LVDC power as well? Each Cat6 could power four devices.

For that matter, we could spend about the same amount of money on a whole-house AC isolation transformer for the electronics. The xformer is connected to incoming 120VAC and neutral and gives us two 60-volt legs with neither referenced to ground. Plug any electronic device into a receptacle and it sees standard 120-volt AC power. There is no ground with all of its nasty side effects.

 

I was reviewing my old posts and came across this one. I never did that experiment so I tried it tonight. I do not know how much cable is left in that 500 foot roll but I do not recall using much more than maybe 25 to 35 feet.

I connected one end to a 500 milliampere 12 volt MR-2 LED bulb and the other end to my Tektronix power supply. I then connected my Fluke multimeter to the bulb. I had to run the supply voltage up to 17.6 volts to get 12.1 at the LED bulb. With 12 volts at the supply I only had 9 volts at the bulb.

Then I shorted the 2 leads at one end and measured the resistance at the other end and it was 11 ohms. Using Ohm's law that works out to about a 5.5 volt drop with a 12 volt supply and a 500 mA load so the observed numbers coincide closely with the theoretical.

 

Voltage drop is by far the biggest problem with a low voltage whole house system.

For a given piece of wire the voltage drop within depends on the amperes flowing and not on the system voltage. Losing 3 out of 120 volts is almost never a problem but losing 3 out of 12 volts almost always is a problem.

You do not want to jack up the voltage at the source end so you have enough volts at the destination end. For a changing load (turning different things on and off) the voltage drop in the wires would change also and the net voltage at the destination would not be stable.

You would need much fatter wires to carry the same number of watts in a lower voltage system compared with a higher voltage system. Telephone systems use currents in the microamperes range or small milliamperes range to reach subscribers about the city so the voltage drop using 22 or so gauge wire is not a problem.