New USB Specification Promises 100W of Power

Blacklaw writes "The group behind the USB 3.0 specification has announced a tweak which could lead to impressive new devices, including large-format displays, printers, and even laptops that are powered entirely from a USB port."

Re:PoE replacement

[fuzzyfuzzyfungus]

PoE, for whatever reason, is absolutely dead in the consumer space; but it is alive and kicking in corporate gear. Not quite 100%, of course, because a PoE switch necessarily costs more than a non-PoE one, and wasting PoE ports on desktops and docking stations doesn't make any sense; but some gigantic portion of the corporate world's APs, IP cameras, access control devices, and similar low-power-and-networked junk are PoE powered...

Re:Finally

[Anonymous Coward]

If you got a shock from your USB port it most likely means you have a broken/disconnected ground lead on your power supply.

This seems like a mess in the making...

[fuzzyfuzzyfungus]

Even with USB2, there was the persistent problem that certain applications(notably 2.5 inch external drives) were right on the edge of what the spec allowed. Some machines played fast and loose, and everything worked fine, some played to spec, and the device wouldn't spin up, or the bus would freak out, or whatever. Despite USB's formalized, standardized, power-request mechanism(100ma on connect, negotiate in units of 100ma for up to 400 more...), the, er... 'inventive'... nature of the peripheral ecosystem always created some uncertainty: Some devices just requested 500ma at all times, to avoid possible brownouts, leading to more spec-compliant busses freaking out about lack of power even when actual draw was well within safe limits, some devices (fans, LED goosenecks, humping dogs) just grabbed the +5 and ground rails and hoped for the best, without any negotiations. Some hubs report themselves as self-powered(and thus good for 500ma per-port) even when they were bus powered(and thus only good for 400ma across however many ports they had). Some others were self-powered; but with wall-warts that could only deliver 500ma to a number of ports smaller than the number available(7-port hubs with 1amp adapters, I'm looking at you...)

This new standard seems like it would simply be a polite codification of this confusion. Particularly at low voltage, 100watts is nontrivial current(and nontrivial power generally, most non-DTR laptop bricks are less than that...) Many PCB layouts would burn a trace trying to deliver that, and you can bet that your garden-variety 10-USB-ports boring desktop isn't going to ship with 1000watts of PSU headroom...

This will mean that, in effect, devices will be able to demand up to 100 watts in a 'compliant' way; but the capabilities of USB ports on the market will vary enormously by device. A laptop with an 85 watt power brick is hardly going to be good for 100watts out of a port. Worse, it might be good for 50 when lightly loaded and fully charged; but only 5 when charging its battery and flogging its CPU... Having a device that only intermittently functions is near worthless, even if it is all entirely standard... A desktop might ship with the ability to push a single port to 100; but then it will either have to beef up its traces significantly, or have the always-confusing-to-dumb-users-and-people-fumbling-behind-desks '1 special blessed "high power" port, and 9 identical-feeling-but-low-power ones' configuration. Fan-fucking-tastic...

While a bit more power on the bus certainly would expand the number of viable, bus-powered use cases, I'm just not sure that such a high 'standard' number can ever be usefully 'standard'. Hooray, it is now officially standard for specialized devices to shove 100watts across a USB bus. Doesn't change the fact that it won't work in 90+% of ports, and will probably burn a fair percentage of cheaper cables. Unless they come up with some sensible set of "tiers", so that people actually know what works with what, this seems like it is going to end in a mess of nominally-USB powered docking stations with wall warts and mini-B connectors, at best.

While its comparative obscurity, and the general lack of bus-powered devices made it less of an issue, Firewire flirted with this problem in its early days: Both available power and available voltage on a given 6-pin port were widely variable: A desktop could, if it so chose, be pumping out 24 volts and reasonably credible wattage. One of the(almost exclusively Apple) laptops with a 6-pin port might be limited to a handful of watts at whatever voltage its battery was set to provide. In practice, much firewire gear just skipped bus power entirely(despite the fact that charging over firewire would have been a very popular consumer camcorder feature, if today's flip-likes are anything to go by), the mixture of widely variable power availability, and the 'i.link' or just 'IEEE1394' connectors entirely without bus power pretty much doomed the widespread availability of bus-powered peripherals. USB's pitiful 2.5watts was rather limiting; but at least you could reasonably assume that it would be there...

Re:Finally

[tibit]

It had nothing to do with 5V, nor with the port being broken. It was an issue with electrical wiring (lack of proper PE - Protective Earth a.k.a. "ground"), most likely. Alternatively, there was no PE connection at all, and you were shunting power supply's leakage current to ground. Most PC power supplies have filtering capacitors between the case and the Live and Neutral conductors. Those capacitors form a voltage divider that puts the case at 50% of live voltage in absence of PE connection, that's the source of the leakage current.