Brad Ideas - Rethinking household/office power, beyond 60hz - Comments

I appreciate all your

gordman — Wed, 02 Jan 2008 05:02:57 -0800

I appreciate all your article, they are all very practical and quite useful for many of us. Rethinking the electrical system might be one of those ideas that can generate a new start. As the matter of fact this should be the main line for our protection and for the environmental protection. I don't see this happening any time soon but the least the we can do is to act smart when it comes to energy consumption. Household appliances have a major importance here, people need to understand how thing go. I just bought myself brand new washer parts and I can tell the difference on my electric bill. But it's not all about energy consumption it's also about radiations and many other factors that can harm us. Now I am thinking to replace all my appliances with "smarter" ones.

Rethinking House Wiring

Ian Robertson — Sat, 22 Jul 2006 03:43:27 -0700

We are indeed stuck with the electrical specifications our power companies send us. Here in the U.K. (and most of Europe) we are provided with 230vac @ 50Hz single or per each of three phase, mostly protective multiple earth (P.M.E.) which means the neutral wire is strapped to the earth conductor at, but not after the incoming main cable terminus. Transforming these voltages is well understood and inexpensive.

In an immoveable house the need is for high-speed very low cost data /voice transmission wherever it is required. WiFi even with MIMO is fine (or will be) but, to this writers mind, it is much better suited to a mobile environment, and it in no way eases the problem of delivering energy to a device. We surely donâ€™t want to run everything on batteries.

Rethinking house wiring probably requires the delivery of power and data simultaneously on the three-wire system we are already used to.

Two types of power are required, medium voltage (up to 400vac) and low voltage (up to +/- 50vdc). The international standard telephonic voltage is minus 48vdc (chosen when Henry Ford was friendly with Thomas Edison!). The rationale for this choice was: - 48 is a multiple of 1.5 (that voltage produced by a single LeclanchÃ© cell, and minus to earth potential so as to prolong the life of exposed copper wire on poles by causing electron flow to travel to the copper (clever eh?).

One type data transmission is required, the collection of packet switched protocols known as TCP/IP at speeds fast enough to cope with digital TV and VoIP. A Protocol now exists for data superimposed on power cables, so there is no need to reinvent the wheel.

The benefits of a combined system are legion: - no more Cat.5, TV or phone cables all over the house, power (medium or low) at every outlet, only one lead to any device, one can still have WiFi if one wants, much lower total cost of installation, the use of co-axial cable instead of twin and earth, the use of a ring-main (almost unique to the UK) could be continued, the Live conductor need not be connected if not required, etc.

One can envisage a mains consumer unit with connections for TV antenna, telephone /ADSL line and WiFi output to ones mobile devices (cell-phone, car, boat, bicycle, pram, etc.).

To invite further discussion, what would be the problems with providing say 230vac between the live and neutral wires and minus 48vdc between the neutral and earth wires? How would these voltages interact? Could any interaction be easily overcome? Only 2 wires in the USA?, one at plus 110vac the other at minus 110vac?

Ian Robertson
2006/07/22

It depends on the real goal

Anonymous — Tue, 03 Jan 2006 19:30:55 -0800

The goals that I see are

Be highly energy efficient
Replace the many custom power warts with one generic power cord

I think that we will be stuck with 100-240V AC distribution within the neighborhood and within the home. This meets the needs of the many high power devices and is the installed base. I had relatives who participated in the conversion of Boston from DC to AC. Given the immense work that it took then I cannot imagine replacing the current AC distribution systems. The need would have to be earth shattering.

For low power devices (under 10W and under 10V) I do expect the outcome to be a split power supply. The generic DC cord will provide up to 1A of variable DC. Then each device will take the variable DC and internally provide regulated power at the needed voltages.

This is much more energy efficient than any low voltage distribution will be. The generic DC cord can be made efficient, although the combination of generic DC with custom regulation is probably not a match for the best switching power supplies. But much of the waste in the low power devices is leakage waste, and that could be made quite low.

I have three devices that are close to this:

My antique Psion 5, whose custom power adapter is about the size of a 3prong plug.
My Zaurus CL3000, which has a really tiny little power adapter. It's 4x4x1.5 cm. It provides 1A at 5V nicely regulated. The size is a bit misleading because the prongs are pivot mounted and can fold into the supply. When folded, the whole thing is just 4x4x1.5
A mystery adapter. I wish it were properly labeled. 1x3.5x1.5 inches, producing variable DC (5-10V) and accepting 45-65Hz 100-240V.

A standard 3-prong plug is 2x1x1 inches. All of these exclude the actual prongs. So current products are close to meeting the size goal. I expect that the generic 10W DC cord will emerge. It can be introduced fairly easily because on one end it can use the existing 45-65Hz 100-240V power grid, and the other can be a generic 10W DC.

You could push the power rating up further but when you leave the domain of pure electronic devices and introduce motors you gain some difficult power supply issues. There are many reasons for the custom voltages when driving motors, and usually the cost tradeoff between custom voltages and difficult mechanical design ends up with custom voltages.

To make this more clear

brad — Tue, 03 Jan 2006 15:11:40 -0800

I am not proposing DC for high power devices, though I think it is suitable for low power devices. Most of what I have plugged in in my home are low power devices with power supplies. Higher voltages are required for higher power, and even higher than 120v makes sense was part of my point, with modern tech.

I am not proposing high-frequency for long haul though it might make sense for short-haul (from transformer to house).

For many devices, high-frequency modest voltage would be easy to convert to the power needed. At a minimum you would not need to do the rectify and chop portion of the typical switched mode supply.

Many of the things that make sense in the car can make sense in the home or office.

It would be nice if plug in low power devices would all centralize on a voltage, but we can't seem to get them to do that. But maybe it can happen.

A somewhat long analysis

Anonymous — Tue, 03 Jan 2006 14:28:06 -0800

DC power has many problems as a household power distribution system, and there may be other answers to the wart problem. You need to consider the effects of wiring, efficiency, etc. There are good reasons why even remote PV powered residences use AC distribution within the home.

I was asked a similar question at a meeting about LED lighting. LED lights use 5V DC and are roughly the same efficiency as flourescents. So a normal bright room light needs 20W (it contains multiple LEDs). At 5V that is 4 amps.

Power loss due to resistance goes as I^2*R. For a 100ft run of 12 gauge copper (typical 20A rated home wiring) R is 0.3 ohms. If you operate at 5V that one light would consume an additional 5W (16*0.3) to heat the wires. If you move up to 10Amps (50W) you also consume a whopping 30W heating the wires. So DC wastes 20-50% of your power. That same 20W light on 200v AC has a wire loss of 0.003W, which is quite insignificant.

For more power hungry devices like PCs, microwaves, or air conditioners a 5V system would need 250amp service. That is utterly impractical. So you will also need 100V+ service in the house. Dual wiring is expensive so you need really compelling reasons to add DC.

AC has other advantages. It is easy to shift AC voltages with transformers. DC to DC voltage shifting is very hard for up, not so hard for down. Internally, CRTs and microwaves need 10-50KVolts. Other common needs are 40v, 10v, 5v, and 3v. It's easy to get all of these with transformers.

Similarly, variable frequency AC is superior for motors. DC is very simple, but unreliable and less efficient. Improvements in power semiconductors have made variable frequency AC motors affordable. They are much more reliable and efficient than DC motors. Railroad locomotives have largely shifted over to variable frequency AC and the proposal for next generation automobiles is variable frequency AC.

The automotive proposal is for the frequency to be up in the 5-20KHz range, and the voltage to be approximately 40V. That lets them replace hydraulics (brakes, steering) and mechanicals (air conditioner, valves) with electronic components. The variable frequency AC components are impractical without modern power semiconductors, but they are also more reliable and more efficient than the hydraulic and mechanical components that they replace. For the devices that need DC (radio, LED lights) the higher frequency AC lets the AC to DC converter be much simpler. It can be put onto a single hybrid chip and integrated into the LED socket or electronics card.

For the home market you have the problem that higher frequency AC has many problems for power distribution. The 50-60Hz AC is really very good for the metropolitan power distribution efficiency. The low frequency minimizes resonance losses to the earth.

The change that I see is different. Some of my newest equipment has AC to DC converters that are no larger than a typical 3-prong plug. They generate variable voltage DC (6-10v). It looks like a poorly filtered power supply, and is probably a diode bridge with modest filtering. That keeps the analog components small. Then there is a DC to DC down converter to 5V or 3V within the device. This kind of splits the power supply into an small AC cord part and a small device part. For power levels up to about 10W this size reduction seems feasible. Above that you need some breakthroughs in analog component sizes. If you pick just a few amperage ratings, e.g., 0.1A, 0.5A, 1.0A controlled off plug shape you end up with a simple DC powering environment where three common cords support any device that needs up to 10V and up to 10W. The device half deals with the particular device requirements.

The USB path is a dead end for higher power requirements. The tiny wires in the USB cable have a high resistance. They limit the USB power to under 0.5A for a reason. If you push it much further you end up with hot wires, significant voltage loss, or both.

Obviously you need to do

brad — Mon, 02 Jan 2006 17:06:23 -0800

Obviously you need to do this but their needs are simple. Clearly one of the primary things you have is an ability to plug in regular household voltage devices, and tiny cheap adapters that put out the DC voltages needed by our many DC devices.

I have a universal laptop adapter, for example. It takes many tips, and puts out different power based on the tip. I haven't examined it in detail, but the tips have 4 wires, so I presume the other 2 wires have something as simple as a resistor which the PS reads to figure out what tip is present and what voltage to provide. This can obviously be done quite cheaply. However, if you look at the price of USB driver chips today, you see that an active device can be very, very cheap too.

A relevant riddle

Anonymous — Mon, 02 Jan 2006 16:45:21 -0800

Q: How did God create the world in seven days?

A: He didn't have to worry about an installed base.

Rethinking household/office power, beyond 60hz

brad — Mon, 02 Jan 2006 13:14:58 -0800

I’ve written before about the desire for a new universal dc power standard. Now I want to rethink our systems of household and office power.

These systems range from 100v to 240v, typically at 50 or 60hz. But very little that we plug in these days inherently wants that sort of power. Most of them quickly convert it to something else. DC devices use linear and switched mode power supplies to generate lower voltage DC. Flourescent lights convert to high voltage AC. Incandescent bulbs and heating elements use the voltage directly, but can be designed for any voltage and care little about the frequency. There are a dwindling number of direct 60hz AC motors in use in the home. In the old days clocks counted the cycles but that’s very rare now.

On top of that, most of what we plug in uses only modest power. The most commonly plugged in things in my house are small power supplies using a few watts. Most consumer electronics are using in the 50-200w range. A few items, such as power tools, major appliances, cooking appliances, heatters, vacuum cleaners and hairdryers use the full 1000 to 1800 watts a plug can provide.

So with this in mind, how might we redesign household and office power…