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USB Power Delivery: Plugging into the Benefits

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Re: USB Power Delivery: Plugging into the Benefits

#61

Post by SchemaLoad »

dotancohen wrote: post #29
hazkoulia wrote: post #4

I'm looking forward to USB-C PD small format factor PC's. A decent amount of room in the PC cases is taken up by the power supply. And if USB-C could somehow provide a range of voltages to the motherboard, SFFPC's could be downsized even more

The issue is that a USB charger is not a USB power supply. A charger does its best, but makes no guarantee of constant power delivery or duty cycle. The power supply absolutely must provide its rated output at 100% duty cycle.

There's also the fact that devices would still need an internal PSU to convert the 28v USB-C to the multiple voltages that all the parts inside need. It would be smaller without the AC to DC conversion though.

Re: USB Power Delivery: Plugging into the Benefits

#62

Post by seba_dos1 »

SchemaLoad wrote: post #56
seba_dos1 wrote: post #52

Earlier quoted context omitted.

> The only slight snag is some cheaper itema refuse to use PD and insist on plain 5V/2A - buy most decent travel chargers have NON-PD ports. Every PD port will handle non-PD USB-C consumers correctly, so not sure why would you care about non-PD ports. There is no "plain 5V/2A" in USB-C though, it's either plain USB (100/150/500/900mA depending on enumeration state), 1.5A or 3A. If you want to advertise exactly 5V/2A,…

I think what they mean is not PD related at all, but the fact some cheap junk has a broken USB-C setup where it's missing the resistor that signals a device has been plugged in and to turn on the 5v power. While USB-A just have 5v live at all times. If you use a USB-A to C cable the device works because it results in a USB-C cable with an always active 5V.

That's why I said "non-PD USB-C consumers", as such junk isn't USB-C compliant - it's just USB-C shaped.

Re: USB Power Delivery: Plugging into the Benefits

#63

Post by tredre3 »

dotancohen wrote: post #15
Animats wrote: post #11

240 watts over a USB-C connector? What next, USB toasters and coffee pots?

That's only a single ampre at standard European mains voltage. It's still a lot of power for those tiny connectors and insulation, but an order of magnitude insufficient for those appliances. I bet that cable gets plenty hot at 200+ watts.

Toasters are frequently only ~750W. That isn't an order of magnitude away from the capabilities of current USB-C.

I doubt they'll ever increase the voltage beyond the current 48V (I was actually shocked that they didn't stop at 24V) so toasters are forever away. But not an order of magnitude away!

Re: USB Power Delivery: Plugging into the Benefits

#64

Post by seba_dos1 »

dotancohen wrote: post #40
Animats wrote: post #36

Earlier quoted context omitted.

USB-C is limited to 48 VDC. Above about 50V, electrical safety codes apply.

Yes, 240 watts is 5 ampres at that voltage - that's why I suspected that the cables get hot. I'm even surprised that a cable so thin is sufficiently insulated for 48 volts. I've seen 24 volt truck wiring arc out of dirty connectors.

You need a e-marked cable to get to 5A with any PD voltage, as a random crappy cable could get dangerously hot indeed. The limit is 3A and 20-21V otherwise.

Re: USB Power Delivery: Plugging into the Benefits

#65

Post by tredre3 »

smallmancontrov wrote: post #12

Speaking of which, does anyone know a line of PD Decoy modules to convert barrel jacks to USB-C without the atrocious behavior of "oh, the charger doesn't have 12V, here's 9V have fun!" that the early ones all did? Ideally I'd like a little red light to come on or something, but I'd settle for not silently browning out the device.

The vflex has a status LED that shows negotiation status. When it fails it will still output 5V, though, they don't seem to have any mosfet to switch the output off entirely.

https://werewolf.us/

I don't think I've ever seen one of those type of converters output anything but 5V upon negotiation failure. Which one did you use that did that? Their logic being "pick the closest available voltage" I presume?

Re: USB Power Delivery: Plugging into the Benefits

#66

Post by exmadscientist »

seba_dos1 wrote: post #54
mschuster91 wrote: post #42

Earlier quoted context omitted.

> Usually the best place to fix it is by getting rid of the bad cables. Usually. No. There is no USB-C to C cable that will charge a badly implemented device with a standards compliant charger. That is the entire point. An USB A to C cable is completely standards-compliant and safe, even if it always supplies 5V on the C end - any standards compliant USB-C device should not activate the MOSFET on its Vbus line unless…

They mean bad USB-A to C cables with no resistor on CC line. Of course this is broken junk which will work with some devices and won't with others. I've also seen cables with resistors on both CC lines, which is also broken but in a slightly subtler way.

Right. That phrase "standards-compliant" in the above comments is doing a lot of heavy lifting.

A lot of devices are not actually standards-compliant. Some are close. (This may actually be worse.)

My experience has been that if the source and sink are broken, they are often hilariously badly broken and it is pretty easy to figure out that they are the problem, if not quite exactly what they've done wrong. But if things are flaky and weird and don't really make sense, it's probably the cable. Try a known-really-seriously-actually-standards-compliantly-good cable and many problems go away, even if the source and sink aren't perfect.

(Many sources and sinks aren't standards-compliant because, even though they easily could be, they're trying to work around the other end not being standards-compliant itself, because that's what you've got to do to sell a product. So they're close but not quite there. This is not always ideal.)

Re: USB Power Delivery: Plugging into the Benefits

#67

Post by exmadscientist »

gsich wrote: post #48
Animats wrote: post #36

Earlier quoted context omitted.

USB-C is limited to 48 VDC. Above about 50V, electrical safety codes apply.

You sure? Those regulations go even higher. https://en.wikipedia.org/wiki/Extra-low_voltage

The controlling standard is usually 62368, and the target is usually being a "Limited Power Source", which is 60V or less, and 100 VA max.

Re: USB Power Delivery: Plugging into the Benefits

#68

Post by TulliusCicero »

JMiao wrote: post #51
edent wrote: post #2

I've basically stopped buying any portable electronics unless they take USB-C. Currently travelling with a laptop, watch, toothbrush, eReader, camera, bug-bite treater, and phone - all charging from the same power brick. I'm guaranteed of getting a replacement cable / charger wherever I am in the world if I need it. The only slight snag is some cheaper itema refuse to use PD and insist on plain 5V/2A - buy most decen…

we are talking about a lightweight charging cable. you can carry more than one. boom, redundancy. being ideological about a cable connector is the nerdy equivalent of jony ive obsessing over macbook thinness.

Nah, being able to reduce to a single cable type is great.

The thing, it's not just about what cables you have at home, or even which ones you bring on a trip. It means if you go out on a trip with a small bag and a battery, you only ever really need one cable. It means you don't have to think about "which cables do I bring?", completely removing a question. That's really nice!

Re: USB Power Delivery: Plugging into the Benefits

#70

Post by crote »

exmadscientist wrote: post #38
dotancohen wrote: post #28

Earlier quoted context omitted.

These companies are not manufacturing the device PCBAs, that is done by dedicated companies such as Flex. The PCBA manufacturing companies have warehouses of different resistors, and 5.1kΩ is extremely common. In fact, most PCB resistor values are quite flexible, to save on SKUs (in practice, to save on loading another carrier on the PnP machine) often if a specific resistor needs a specific value then all (or most o…

I was speaking a little more towards the AliExpress end of things, which is a sadly high proportion of the devices out there. For the midsize CMs and up, you're right, they've got piles and piles of stuff and don't charge by the reel loaded. 5.1k is a surprising resistor value, a lot of modern designs don't really have anything else in that area. I'm often not able to combine anything with it when I'm cost reducing.…

Heh, I would've argued the opposite.

5.1k is about the middle of the generic "some kind of pullup" range of 1k-10k, so it's a perfectly fine option for strapping resistors or for a non-critical I2C bus.

4.7k would of course have been better because it's an E6 value (+-20 via the spec) rather than E24, but it's still a value I would expect any PCBA house to have in stock at all times.

But I agree, 1k or 10k would be the obvious no-brainer. I reckon there's probably a technical reason for it, as it does act as a voltage divider together with the Sink pullup, so perhaps there are some restrictions there with the multiple values it needs to distinguish.

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