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The humble USB cable is part of an electrical revolution

economist.com

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Re: The humble USB cable is part of an electrical revolution

#11

Post by srinivasanv »

em3rgent0rdr wrote: post #8
pkulak wrote: post #4

Anyone know how this standard actually works? I think right now Android phones tend to short the data lines and Apple uses some system of voltages to communicate that it's high power, which means that the other device usually gets stuck pulling 0.2 amps. How does this new standard tell the device it can supply 100 watts? And does this mean that iOS and Android will be stuck on 0.2 amps? Can you plug a legacy device o…

http://www.usb.org/developers/powerdelivery/ USB has both power and data lines. This new standard can use data lines to negotiate power delivery, I believe. I'd expect will still be backwards-compatible of course. I would think the only allowable voltage would be 5V, as is currently.

100W at 5V would be a 20A current, which is sort of high.

http://www.usb.org/developers/powerdelivery/PD_1.0_Introduct... Page 9. There will be different voltage levels: 5V, 12V, and 20V.

Re: The humble USB cable is part of an electrical revolution

#12

Post by em3rgent0rdr »

srinivasanv wrote: post #11
em3rgent0rdr wrote: post #8

Earlier quoted context omitted.

http://www.usb.org/developers/powerdelivery/ USB has both power and data lines. This new standard can use data lines to negotiate power delivery, I believe. I'd expect will still be backwards-compatible of course. I would think the only allowable voltage would be 5V, as is currently.

100W at 5V would be a 20A current, which is sort of high. http://www.usb.org/developers/powerdelivery/PD_1.0_Introduct... Page 9. There will be different voltage levels: 5V, 12V, and 20V.

yup, I had read that and corrected exactly same time as you :)

Re: The humble USB cable is part of an electrical revolution

#13

Post by quesera »

simcop2387 wrote: post #2

With the new USB Power Delivery spec this can finally make sense to really start thinking about. Being able to power things that are "non-trivial" as far as power goes would make this go a long way. Imagine your sound system being powered off of a very clean DC power source, would be an audiophile's dream. 20V and 100W would make for a lot of nice options for powering things.

> 20V and 100W would make for a lot of nice options for powering things.

Requires a pair of 17AWG stranded wires for a 2m run, allowing 3% cable loss.

For comparison, cat6 is 23 or 24AWG stranded, and US residential power wiring is typically 12 or 14AWG solid core. Smaller numbers are bigger, less flexible wires.

I guess it won't work with microUSB contacts, or at least not at full power.

Re: The humble USB cable is part of an electrical revolution

#14

Post by em3rgent0rdr »

kabdib wrote: post #3

It's going to be interesting, from a security standpoint. One of the original cracks on the PS3 was via the USB stack. I'd not go plugging my computers or phones into jacks that I don't necessarily control. I can see a market for buffering devices that allow power through, and perhaps do power negotiation for you, but that do not allow data traffic. I believe these devices already exist. though I don't know how sophi…

surely this could be a software fix: tell usb driver to use special mode that is only allowed to use data line to negotiate power levels, before you plug into an untrusted power source.

Re: The humble USB cable is part of an electrical revolution

#16

Post by sigvef »

kabdib wrote: post #3

It's going to be interesting, from a security standpoint. One of the original cracks on the PS3 was via the USB stack. I'd not go plugging my computers or phones into jacks that I don't necessarily control. I can see a market for buffering devices that allow power through, and perhaps do power negotiation for you, but that do not allow data traffic. I believe these devices already exist. though I don't know how sophi…

There are USB condoms http://www.usbcondoms.com/

Re: The humble USB cable is part of an electrical revolution

#17

Post by nine_k »

em3rgent0rdr wrote: post #14
kabdib wrote: post #3

It's going to be interesting, from a security standpoint. One of the original cracks on the PS3 was via the USB stack. I'd not go plugging my computers or phones into jacks that I don't necessarily control. I can see a market for buffering devices that allow power through, and perhaps do power negotiation for you, but that do not allow data traffic. I believe these devices already exist. though I don't know how sophi…

surely this could be a software fix: tell usb driver to use special mode that is only allowed to use data line to negotiate power levels, before you plug into an untrusted power source.

That special mode code and negotiation code is what malware authors will target.

For hostile / high security environments, I'd rather have it in a special charging-only hub (good luck pwning such a device) that physically lacks the data wires on the output socket.

Re: The humble USB cable is part of an electrical revolution

#18

Post by GammaDelta »

ams6110 wrote: post #6

One problem with low-voltage DC is that according to Watt, to achieve equivalent power (watts) at a low voltage, current is higher. And heat is proportionate to current squared. So you can't send a lot of power at low voltage because you lose a lot to heat. That means low-voltage runs have to be kept fairly short, or very low power, limiting their usefulness.

Funnily enough USB's inability to work over longer cable lengths works in its favour here. Generally we don't rely on anything working over 3 metres.

Wikipedia says "the maximum power supported is up to 60 W at 20 V, 36 W at 12 V and 10 W at 5 V" [1]. For a typical 3 metre 20 gauge USB cable 10 W power delivery will cause a voltage drop from 5 to 4.6 V. This is within the +0.25/-0.55 specified for USB 3 [2].

Since nobody can rely on the 5 V from USB to be exactly the charging voltage they need, there will probably be switchmode regulators in-line anyway. Device manufacturers will just have to spec these up a bit to accept higher input voltage if they want more than 10 W.

[1] http://en.wikipedia.org/wiki/USB_Power_Delivery_Specificatio... [2] http://en.wikipedia.org/wiki/USB

Re: The humble USB cable is part of an electrical revolution

#19

Post by sliverstorm »

x0x0 wrote: post #5
kabdib wrote: post #3

It's going to be interesting, from a security standpoint. One of the original cracks on the PS3 was via the USB stack. I'd not go plugging my computers or phones into jacks that I don't necessarily control. I can see a market for buffering devices that allow power through, and perhaps do power negotiation for you, but that do not allow data traffic. I believe these devices already exist. though I don't know how sophi…

(I'm not an engineer). I a similar article; iirc android phones could be owned by plugging them into a hostile usb connection. I wonder, though, if you couldn't produce a simple adapter that just drops some of the pins? Maybe I don't know enough about usb.

You can make a power-pin-only USB connector, but I believe that precludes requesting high-current mode (i.e. you are stuck in 100mA mode)

Re: The humble USB cable is part of an electrical revolution

#20

Post by jcampbell1 »

kochb wrote: post #15

This was posted a month ago as well, discussion: https://news.ycombinator.com/item?id=6591186

I find it notable that this article entirely ignores the EU's Common Electrical Power Supply law (http://en.wikipedia.org/wiki/Common_External_Power_Supply), which effectively mandated that all smart phones sold in the EU use micro USB for power. This had a swift and noticeable effect in the diversity of connectors in phones (basically Apple is the only maker that doesn't use micro USB and this change happened at the exact time of the law). The emergence of USB as The Way Phones are Charged didn't happen as a magic emergent property, but via considered government regulation. Government: it can actually work.
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