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Edison’s revenge DC Power Distribution Via USB

The Economist has an article on the increasing popularity for using USB connectors for DC power distribution, declaring "The humble USB cable is part of an electrical revolution. It will make power supplies greener and cheaper" - Edison’s revenge.

Most phones and other small gadgets can charge from a simple USB cable plugged into a computer or an adaptor. Some 10 billion of them are already in use. Hotel rooms, aircraft seats, cars and new buildings increasingly come with USB sockets as a standard electrical fitting.

Now a much bigger change is looming. From 2014, a USB cable will be able to provide power to bigger electronic devices. In the long term this could change the way homes and offices use electricity, cutting costs and improving efficiency. ...

The big change next year will be a new USB PD (Power Delivery) standard, which brings much more flexibility and ten times as much oomph: up to 100 watts. In his London office Simon Daniel, founder of Moixa, a technology company, charges his laptop from a prototype souped-up USB socket. The office lighting, which uses low-voltage LED (light-emitting diode) lamps, runs from the same circuit. So do the monitors, printers and (with some fiddling) desktops. Mains power is only for power-thirsty microwaves, kettles and the like.

That could presage a much bigger shift, reviving the cause of direct current (DC) as the preferred way to power the growing number of low-voltage devices in homes and offices. DC has been something of a poor relation in the electrical world since it lost out to alternating current (AC) in a long-ago battle in which its champion Nikola Tesla (pictured, left) trounced Thomas Edison (right). Tesla won, among other reasons, because it was (in those days) easier to shift AC power between different voltages. It was therefore a better system for transmitting and distributing electricity.

But the tide may be turning. Turning AC into the direct current required to power transistors (the heart of all electronic equipment) is a nuisance. The usual way is through a mains adaptor. These ubiquitous little black boxes are now cheap and light. But they are often inefficient, turning power into heat. And they are dumb: they run night and day, regardless of whether the price of electricity is high or low. It would be better to have a DC network, of the kind Mr Daniel has rigged up, for all electronic devices in a home or office.

This is where USB cables come in. They carry direct current and also data. That means they can help set priorities between devices that are providing power and those that are consuming it: for example, a laptop that is charging a mobile phone. “The computer can say ‘I need to start the hard disk now, so no charging for the next ten seconds’,” says Mr Bhatt. The new standard, with variable voltage and greater power, enlarges the possibilities. So does another new feature: that power can flow in any direction.

This chimes with another advantage. A low-voltage DC network works well with solar panels. These produce DC power at variable times and in variable amounts. They are increasingly cheap, and can fit in windows or on roofs. Though solar power is tricky to feed into the AC mains grid, it is ideally suited to a low-voltage local DC network. When the sun is shining, it can help charge all your laptops, phones and other battery-powered devices.