USB Power Delivery: Plugging into the Benefits

Posted by mooreds 6 days ago

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Comments

Comment by edent 2 days ago

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 decent travel chargers have NON-PD ports.

Amusingly, most of the buses I've taken recently also have USB-C ports on them for ad hoc charging. Perhaps one day EVs will use USB-PD-Max rather than CCS :-)

Comment by ElijahLynn 2 days ago

Same!

I've also returned a few USB devices that ship with a USB-A to USB-C cable and ONLY charge in that mode, they also MUST charge with USB-C PD.

The two so far were a therapy light and some Zippo hand warmers. Like, who in the hell would design a device that has a USB-C port on it where only a fraction of chargers will work on it. It feels even worse than proprietary charges, because you see a USB-C port on it and think, oh I have a plug that fits it, and then it doesn't F**ing work. Idiot engineering/product teams, making the world suck with their falsely advertised USB-C ports. If anyone of you are on a team that ever makes this decision, just know that it is a stupid decision, and jump ship when you can.

Comment by myself248 2 days ago

The thing is, making a 5v-only device PD-compliant is literally one resistor. It costs well under a penny.

It's pure ignorance, not a decision, but the lack of one. Lack of caring, lack of having an actual engineer involved, just slapping an oval-shaped port into a product where a trapezoidal port had been, and blindly thinking that magically makes it spec-compliant.

Or not thinking about the spec at all.

I return these devices too. Lots of them. My e-commerce returns over the last year are probably 50% PD non-compliance, 50% all other defects combined.

Comment by exmadscientist 2 days ago

It's two resistors, actually. But they cost $0.0003 each (that's 0.03¢, or just around 3,333 of them for US$1) from distributors. Though there appears to be a bit of a stock crunch right now.

So... yeah.

The bigger issue is not really the parts cost, it's the fact that it adds an extra part to the design that has to be purchased and tracked and assembled and blah blah blah. This is the real reason it often gets left off on the bottom-of-the-barrel products. Many times there is no other use for a 5.1kΩ resistor. And it might not even fit well at the cheap sizes (0603 or 0402), and going down to 0201-capable assembly factory flow just for these two resistors is not going to happen.

Comment by dotancohen 2 days ago

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 of) the other resistors will use that value.

Comment by exmadscientist 2 days ago

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. 4.7k, sure, but there aren't a lot of those either... 2.2k is just not close enough a lot of the time (or ends up as 1k), and same for 10k. So, sadly, it often does stand alone.

Comment by crote 2 days ago

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.

Comment by exmadscientist 2 days ago

The 4.7k "default pullup" is an old-school 5V TTL thing. It works really well for TTL inputs. But CMOS inputs don't really care very much, especially if they aren't toggling or if there's a bit of hysteresis on the input stage (which there often, but not always, is). There seem to be 10k resistors in every design so CMOS pullups often end up at 10k. If power savings are a concern, especially if you need a tie-off more so than a pull resistor, 10k-100k is a perfectly valid range, and I've even used 1M in extreme circumstances.

Usually 5k is a little too weak for I²C. Rule of thumb is that you want to be around 1mA, so for a 3.3V system you start at 3.3k. Generally 1.8k to 3.3k ends up being a pretty common range. More current is usually better than less current, so even at 5V where 4.7k might be OK (if you're even at 5V Vdd these days), going stronger is often a good idea. If power savings is a concern, or if timing's somehow important (did you find another touchy badly behaved I²C device? say it isn't so!) then it might be time to break out the active pullup structures (mostly current source type things). Once this is done and tested it tends to get fossilized, for good reason, so this one won't usually get swept up in a standard-effort cost reduction pass.

Comment by dotancohen 2 days ago

Interesting, thank you. That is an end of the market that I have not seen.

I wonder if PD will cause a comeback of that value as more and more legacy device refreshes move to USB-C plugs.

Comment by helterskelter 2 days ago

There's an otherwise decent shortwave radio out there that was originally charged with a micro-usb, then they released a "new" USB-C model...except it will only charge with a 5V brick because they literally just swapped out the ports. Really annoying.

Comment by dabluecaboose 2 days ago

Oh man, please tell me it wasn't the CC GP-7. I have the micro version and have been hemhawwing about updating it.

Comment by helterskelter 2 days ago

You mean the CountyComm? If so, I'm 99% certain that radio is a rebranded Tecsun PL-360, which is in fact a 5V. I love Tecsun, but why they would cheap out on the USB-C refresh is beyond me.

https://www.tecsun-radios.com/product/pl360-radio-receiver/

Comment by dabluecaboose 2 days ago

Looks more like the 368, but yeah. Good call!

Sounds like the juice may not be worth the squeeze on a USB-C refresh if I have to use an A-to-C cable for it anyway

Comment by dotancohen 2 days ago

I'd imagine that a significant portion of the shortwave radio community is capable of soldering in the two resistors.

Comment by wpm 2 days ago

If the board had unpopulated 0802 pads, I absolutely would be.

Comment by dotancohen 2 days ago

Is there not enough room for a through-hole resistor to just hang out in the air? Most devices I've opened seem to have more than enough room, so long as one is skilled enough with the small chisel tip.

Comment by myself248 2 days ago

Yeah, it's a significantly trickier proposition when the pads aren't there.

The contacts are in the connector, you just need to bring them out and get the resistor on them, which is frankly a pain I shouldn't have to endure when USB-C has been out for 12 years. None of this is rocket science, the manufacturers just aren't feeling the pain.

Comment by 21 hours ago

Comment by megous 2 days ago

Only if the device's consumption is < 2.5W, which is what a USB 2.0 computer USB-A's data port limit is. Anything above that, compliance gets a bit more involved and complicated.

Comment by seba_dos1 2 days ago

Yes, but that's the case with microUSB as well. In fact, refusing to work with underpowered source is easier with USB-C.

Comment by megous 2 days ago

It's certainly not easier. Type-c power sink can advertise USB default, 1.5A or 3A easily. USB default is not necessarily underpowered. You still have to use BC1.2 to see if the source is actually underpowered.

If you're just a microUSB device, you'll also check based on BC1.2. And you can ignore CC/Rp check. It's actually simpler.

I guess you can assume anything advertising itself as USB default is underpowered, but then you'd be wrong.

Comment by seba_dos1 2 days ago

It sure is. You can just spec it to require a USB-C 7.5W/15W source and then you can gate the operation behind a simple analog circuit and Bob's your uncle. No such way with microUSB until you implement BC1.2, which you don't have to support with USB-C (though it's certainly nice when you do).

> but then you'd be wrong

Not at all, it would just miss signaling it's not compatible with, just like with all sorts of proprietary signaling protocols out there. The point is that with microUSB you have no other way, you have to implement BC1.2 (or some proprietary spec) which is often more complex than a comparator on CC line.

Comment by megous 1 day ago

Yes, that way your type-c device will also be refusing to work with many sources that can provide enough power, that is with anything advertising USB default power.

For proper detection of actually underpowered source without awful lot of false negative results, you always need BC1.2. You're just adding type-c CC pins circuitry on top maybe to detect what power is availabe in non-default-usb-power scenarios. If you just use CC pins for detection, a lot of your users will not like you, and will not understand why they can't charge your type-c port featuring smartphone or whatever with a perfectly capable 2.1A/5V charger connected via USB A-C cable.

Been there done that.

Comment by seba_dos1 1 day ago

Yes, that's all true. It's also irrelevant, as USB-C devices aren't required to support BC1.2, and the same concern applies to any proprietary signaling method you won't handle. "This thing requires 15W USB-C power source" is easily understood, regardless of existence of >=15W USB-A power bricks using QC3.0 or whatever else.

Supporting BC1.2 in a smartphone won't make it any more complex than it already is (been there done that). We're talking about simple equipment here, where handling USB-C power correctly can be easily done without any ICs.

Comment by simoncion 2 days ago

> I've also returned a few USB devices that ship with a USB-A to USB-C cable and ONLY charge in that mode...

By "that mode", do you mean "1.5A @ 5V" permitted by BC, or do you mean "3A @ 20V" permitted by non-type-C PD?

> Like, who in the hell would design a device that has a USB-C port on it where only a fraction of chargers will work on it.

Who in the hell would design a charger that can do Type-C PD but can't do either pre-Type-C PD or BC? Does the charger in question also shit the bed when a USB 1.0 device attempts to draw 100mA @ 5V? I hope not! Were it me, I'd return that crappy thing for a refund.

Comment by duskwuff 2 days ago

> By "that mode", do you mean "1.5A @ 5V" permitted by BC

Neither - OP means devices with missing CC resistors which will fail to charge with a compliant PD source. (The A-to-C cable works because it provides 5V Vbus unconditionally.)

Comment by exmadscientist 2 days ago

The A-to-C cable often does not work because the resistors are supposed to be in there.

So if you are having complete charge failures, try a different cable.

Comment by ssl-3 2 days ago

That's close, but it's not quite complete. There seems to be lots of confusion here, and that's natural: It is confusing.

For just-getting-power from a USB A port into a USB C peripheral: There are supposed to be 2 resistors in the peripheral device [always], and also 1 resistor within the cable for USB-to-legacy cables[1]. That's 3 resistors, total, to get a relatively dumb USB-C equipped peripheral device to reliably charge from both USB A and USB C hosts/chargers/whatevers:

The cable itself: It gets an internal 56k pullup resistor between Vbus and USB C pin A5 -- which is the CC line [yes singular]). This resistor signifies the capabilities of the host/charger/whatever for devices that care (some do care, some do not care).

The peripheral: This minimally needs two pulldown resistors [commonly 5.1k], between each of CC1 and CC2 [yes a plurality] and ground[2]. This tells a compliant USB C host/charger/whatever "It's OK! Send the juice juice!" regardless of connector orientation.

[1]: https://www.usb.org/sites/default/files/USB%20Type-C%20Spec%... section 3.5

[bleh]: Again, it is a confusing thing. Nobody said that dealing with such flexible, ambidextrous connections would be simple. CC performs a lot of different tasks: It can be a bidirectional serial bus for active PD negotiations, and/or a resistor network for passively dealing with power, and it's the bit that performs detection of cable orientation for applications where that matters, and it probably does other stuff too.

That single little wire is clever AF. It'd be simpler to use multiple wires instead of just one, but that would take more copper. Copper is expensive, and we each save a tiny bit of money (or a large pile of money globally) by using less copper instead of more of it.

Comment by exmadscientist 2 days ago

My point, which matches what you've written out in more detail, is that there's supposed to be stuff (resistors) in the cable, stuff which is often not there. There are plenty of these abhorrent cables in the wild. And when you come across one, things get weird, because some sources and sinks deviate from the standard in ways that make them work with these bad cables. Others don't do that. (I believe there were a lot more abhorrent cables in the early days, and thus began the chain of accommodation....)

So unless your cable is known-good, if you are having trouble, trying a different cable should be the first thing you do. It really does often get things working.

Contrarily, if you have identified a naughty cable, it should be immediately widlarized.

Comment by ssl-3 2 days ago

I gathered that you knew that. I'm mostly just trying to complete the picture for those following along at home, who might find some of this resistor business to be a bit weird compared to the USBs of yore.

Except the old ways were weird in unseen ways, too. Some combinations of cable, phone, and charger worked well and some barely worked at all.

We're in much better shape with USB C and PD. It's generally a good, forward-looking way of doing all kinds of things.

I just wish the cables and ports were better-marked, and that manufacturers stopped fucking around by making non-compliant stuff, and that there were a clear way with two battery-equipped USB C devices to unequivocally declare that a particular one will charge the other (and not the other way 'round).

And yes: The non-compliant widgets should ideally be named, shamed, and Widlarized -- not simply tolerated or worked around.

Comment by megous 2 days ago

A-C cable assembly always works, CC signal is connected within the cable to Vbus via 56kOhm resistor, but that's only relevant to the downstream port, not to the upstream USB-A power sourcing port which does not have access to the CC signal. Upstream port provides power unconditionally within some limits depending on port type (CDP/DCP/USB3.0/2.0 data port/...).

Comment by exmadscientist 2 days ago

That's how it's supposed to work, yeah.

But there is some trash out there in the world. A lot of it, actually.

Some naughty cables work with some naughty chargers work with some naughty devices. Postel's Law in action, I guess?

Usually the best place to fix it is by getting rid of the bad cables. Usually.

Comment by mschuster91 2 days ago

> 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 it successfully negotiates via CC.

Comment by seba_dos1 2 days ago

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.

Comment by stephen_g 2 days ago

But it’s not what anyone was talking about. Such a cable should be really quite rare because it’s unlikely to work at all in most situations, whereas devices with USB-C ports that don’t work with PD chargers (due to a cent’s worth of missing Rd resistors) are irritatingly common, because they do work with USB-C to A cables!

Comment by seba_dos1 2 days ago

Huh? It seems clear to me that this is what exmadscientist was talking about, any other interpretation just doesn't make sense.

And no, such cables would still work in plenty of cases. You usually get them by having them bundled with devices they do work well with. In fact, they always work fine with the kind of devices you mention. These cables aren't as common as USB-C-shaped junk that's missing resistors on the receptacle, but I stumbled upon them anyway and I didn't really try to.

Comment by exmadscientist 2 days ago

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.)

Comment by megous 1 day ago

You may wish to re-read the type-c specification, especially 4.5.2.2.3.2:

"A USB 2.0 only Sink that doesn’t support accessories and is self-powered or requires only default power and does not support USB PD may transition directly to Attached.SNK when V BUS is detected."

or 4.5.2.2.5:

"A port that entered this state directly from Unattached.SNK due to detecting V BUS shall not determine orientation or availability of higher than Default USB Power and shall not use USB PD."

or 4.5.2.2.11.2:

"The port shall transition to Attached.SNK after tCCDebounce if or when V BUS is detected."

CC detection, let alone PD negotiation is not needed. You can draw up to 2.5W right away from Vbus and be standard compliant without wiring anything to CC signals.

Of course if you try this with a DRP device like a smartphone, you'll get no power. But that's not really an issue for type-c chargers or USB A-C cable assemblies.

Comment by 2 days ago

Comment by blacksmith_tb 2 days ago

I'm hoping we'll see most e-bikes at least use 240W usb-c pd charging (I figure I have about a decade until I will wish I had some assist and buy one, so probably by then, they'll have gotten there...)

I also have assorted products that won't charge c-to-c (some from respectable manufacturers even, like Philips), but I see you can get little adapters with 5.1K resistor you plug into said crappy devices to cover that, I will have to try some out.

Comment by seba_dos1 2 days ago

> 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, you need PD.

Comment by SchemaLoad 2 days ago

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.

Comment by seba_dos1 2 days ago

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

Comment by ianburrell 2 days ago

I think you are confusing the devices with USB-C that require USB-A, and devices that charge the standard USB-C 5V/3A/15W. The USB-A ones cheaped out in including the resistors that signal legacy USB mode, they work with the ones in the cable or adapter.

Lots of people assume that USB-C always uses USB-PD, but the basic signalling is done with resistors. Lots of devices only need 15W, and it is better than USB-A charging. If you want faster charging, buy more powerful chargers.

Comment by m463 2 days ago

For travel I have a bunch of cables with adapters on the end (choose usb-c, lightning, micro-usb). Can use usb-c, but have the ability to use the others.

It has helped out in a bunch of unexpected situations (usually someone else's device)

Comment by mcsniff 2 days ago

I'll bite. What type of watch do you have that has a direct USB-C port on it?

Comment by edent 2 days ago

This one - https://shkspr.mobi/blog/2025/08/i-bought-a-16-smartwatch-ju...

No need for a magnetic dongle. I literally shove a USB-C cable in there, charge for a couple of hours, then get a week+ of use. Does step count, notifactions, calls, etc.

There's more to the world than Apple and Android watches.

Comment by margalabargala 2 days ago

They may be talking about something like the OnePlus watch, which does not have a usb-C port on it, but the charger device for the watch takes usb-C.

Comment by dgunay 2 days ago

I have one and it's such a fantastic design. When I need to travel I just throw a tiny puck in my bag and it charges off the same brick that charges everything else I bring.

Comment by user_7832 2 days ago

> Amusingly, most of the buses I've taken recently also have USB-C ports on them for ad hoc charging.

I've been pleasantly surprised recently when I plugged in my OnePlus into the bus in a medium/small Belgian city and saw the supervooc animation. (And it was actually fast charging, a 8 minute ride gave about 15% battery.)

For anyone wondering about technical details, PPS chargers now show up as supervooc apparently.

Comment by codethief 2 days ago

What toothbrush do you have? I've been looking for a USB-C charger for mine (standard Oral-B toothbrush) but the only ones I've found were from no-name Chinese brands and didn't work at all.

Comment by edent 2 days ago

This one. No separate charger, just plug the USB-C cable in to the toothbrush.

https://www.amazon.co.uk/gp/aw/d/B0F8BD3922

Comment by XorNot 2 days ago

I bought this one and it works: https://www.amazon.com.au/gp/aw/d/B0BS1VXS6L?psc=1

Comment by cainxinth 2 days ago

I’m almost fully converted, except my Gen 1 AirPod pros are somehow still kicking and thus I still need a Lightning cable.

Comment by MrBuddyCasino 2 days ago

You can always use a „PD Decoy“ if the voltage is USB compatible. A 5 / 9 / 12 / 15 / 20 Volt barrel plug is trivially USB powerable.

Comment by dreamcompiler 2 days ago

TIL you can treat bug bites with something electrical.

Comment by PetitPrince 2 days ago

Yeah it uses a tiny ceramic heating element to heat the bite area up to uncomfortable temperature. It's supposed to denature the toxin and/or counter inflammation. Either way it does reduce moskito itchiness with me.

Comment by sieabahlpark 2 days ago

[dead]

Comment by JMiao 2 days ago

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.

Comment by vel0city 2 days ago

The number of times I went on a week-long vacation as a kid only to find out I didn't have just the right cable to charge my whatever-portable-entertainment thing was way too high. Oops, not the right cable for the portable DVD player. Oops, not the proprietary Gameboy SP adapter. Oops, not the right cable for the camera. Oops, not the right cable for the Genesis Nomad.

Forget that noise. Now its all one cable. Laptop, game console, phone, wireless headphones, reading device, even things like flashlights and lanterns. All one cable, can all work with the same extra battery packs and the same power cords.

Comment by tredre3 2 days ago

Assuming your comment is only about proprietary cables that have usb a/c on the charger side, I tend to agree. Sometimes the device's form factor or function simply cannot accommodate usb-c without trade-offs.

I did lose my shaver's cable whilst travelling once, so I had to go to the barber to look presentable before a meeting. Not a big deal, but it goes to show that it happens. Had it been USB of any description, I could have bought one anywhere.

But then again I could have just as easily lost/broken the device itself and be in the same situation, so shrugs.

Comment by TulliusCicero 2 days ago

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!

Comment by itnerd 2 days ago

Does PD include a specification that allows a client device to share its current battery level? How does Apriv know which device “needs” a high output level?

> Using dual-port modules, the system recognizes that, say, one smartphone battery in the vehicle is at 5 percent of capacity and a second phone is at 75 percent. The programming module gives the former device 100W and the latter 25W.

Comment by mtabini 2 days ago

USB-PD 3.1 provides both a Get_Battery_Cap message, which asks the sink to tell the source the capacity of its battery) and a Get_Battery_Status message, which asks the sink to inform the source about the current charge of its battery.

Here's an example capture of an exchange between my MacBook Pro and iPad: https://imgur.com/a/8rZlN9X

The iPad responds to Get_Battery_Cap with Battery_Capabilities, which reports the total capacity in Wh:

USB Vendor ID: 0x05AC Product ID: 0x0000 Design capacity: 280 Last full-charge capacity: 280 Battery reference: valid

And then when the MBP asks for battery status, the iPad returns a Battery_Status message:

Battery is present. Present capacity: 14.2Wh Charging state: charging.

Later on, as the charging continues, the iPad will issue an Alert message:

Reported alerts: Battery status changed. Affected batteries: Fixed battery slots: 1

And then the MBP will send a Get_Battery_Status again, and so on. (Example capture here: https://imgur.com/a/TI5maV0

What's really cool is that this exchange happens both ways—the iPad also sends a Get_Battery_Cap message to the MBP, because it is also capable of acting as a source, and, if the laptop's battery drops sufficiently low, the source/sink roles may swap (using a DR_Swap message) so that the iPad ends up charging the MBP!

Comment by seba_dos1 2 days ago

I think you meant PR_Swap rather than DR_Swap.

Comment by mtabini 2 days ago

I did, you're absolutely right. Thanks for the correction!

Comment by seba_dos1 2 days ago

Yes, since PD 3.1 (see "Get_Battery_Status" request).

Comment by hazkoulia 2 days ago

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

Comment by ranger207 2 days ago

I have a couple like that in my mini rack. The problem is the power supply: these take 65W, so I figured I could get a quality 140W charger and power them both, but it turns out that things like "unplugging something else" would kill their power. I had to spend a lot more on a StarTech charger to get the performance I needed

Comment by crote 2 days ago

Yeah, it's due to power renegotiation.

It wants to supply the maximum power possible as you don't want a device which can charge faster stuck at a lower rate, so it wants to renegotiate with the sink, and the lazy way to do that is a full reset.

Comment by chocolatkey 2 days ago

Which startech product did you end up getting? One of the hubs or chargers? I have a similar issue with various USB-C rack devices

Comment by ThatPlayer 2 days ago

Jeff Geerling has done a review and follow-up on one: https://youtu.be/twoAW0eLiXY

I've considered just getting a bunch of 65W USB-C buck converters and DIY one.

Comment by wongarsu 2 days ago

A lot of SFF PCs already come with a power brick. Just with a 12V barrel jack instead of a USB-C port. Compared to that design you really wouldn't safe much space. Though I admit that USB-C would be convenient. Maybe with a tiny battery

Comment by dotancohen 2 days ago

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.

Comment by SchemaLoad 2 days ago

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.

Comment by crote 2 days ago

This is already the case today. Those mini pcs often take 19V, so it can use cheap and abundant laptop PSUs, which use that voltage for battery chemistry reasons.

Literally nothing inside it uses that voltage, so it'll just get downconverted to the single-digit voltages the chips actually need.

Comment by exmadscientist 2 days ago

> And if USB-C could somehow provide a range of voltages to the motherboard, SFFPC's could be downsized even more

You reeeeeeally don't want to do that. Cable inductance is a big deal, among other issues. You want the main DC-DC regulators on the board, usually right at the load, for the main loads. Most of the PSU bulk is for dealing with mains itself: handling 50/60Hz or mains isolation is just physically large. Getting in secondary 20V DC (or so) from a single connector and then regulating it down on board is pretty much the ideal solution.

(I can't even begin to comprehend the horrors of a USB-PD negotiation involving multiple voltages. It's already the worst standard I've ever had to deal with.* Don't make it worse!)

(* Not hyperbole, it is truly, truly awful. At least things like 60601 are bad because, you know, they're covering lots of stuff like lifesaving medical devices. USB-PD is... holy hell, it is just bad.)

Comment by seba_dos1 2 days ago

I quite like PD 2.0 when ignoring the legacy USB-A stuff. It's semi-elegant. 3.0 and further made it an abomination though.

Comment by mschuster91 1 day ago

> I can't even begin to comprehend the horrors of a USB-PD negotiation involving multiple voltages. It's already the worst standard I've ever had to deal with.

Yeah but usually you don't have to deal with that yourself but have some sort of chipset that handles all the USB-C PD and, optionally, even data-lane muxing stuff.

Comment by contingencies 2 days ago

Existing solution @ https://github.com/vk2diy/hackbook-m4-mini

Comment by omh 2 days ago

There are some SFF PCs that can take USB-C power.

Lenovo have some,but sometimes require adapter cards. And a few of the Chinese N150 units will take PD power

It's great for hot swapping and more portable than a laptop.

Comment by quotemstr 2 days ago

I'm appreciating this recent spate of "Why Underappreciated Technology X is Good" articles. (For example, the recent EXIF one.) It's way too easy focus on the bad and foment outrage. But the world we inhabit is pretty good, and it's good to understand why it's pretty good.

Comment by smallmancontrov 2 days ago

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.

Comment by tredre3 2 days ago

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?

Comment by miladyincontrol 2 days ago

iirc theres ones that do. However I dont recall there being any clean fix to the amperage constraint issues. Especially when a lot of usb-c chargers will vary output as they heat up with usage.

Which is kinda part the issue, usb-c charging bricks, they aren't usb-c power supplies, there is no expectation of sustained output capacity. Thankfully at least some the multiport ones have renegotiation more or less solved cleanly rather than what is essentially rebooting the PD controller.

Comment by SchemaLoad 2 days ago

You ideally want to get a USB-C brick that's over specced and from a reputable brand. Like if you get a macbook 140w usb-c brick it will work fine with everything.

Even for actual PSUs it's always been the advice that you want a decent amount of headroom to avoid issues.

Comment by m463 2 days ago

sounds like someone needs to create a DC-DC charger

Comment by smallmancontrov 2 days ago

I mean, so long as it cuts off and throws a red light I'll figure it out, especially if the brick got toasty, and then I can find a new brick. My problem is that "best effort" seems to be almost universal behavior among PD triggers and it multiplies the failure modes.

Comment by Havoc 1 day ago

Don’t think you’ll find it cause it’s not an issue with the decoy - that’s the expected behaviour. 12v isn’t mandatory. Which is insane but here we are.

On the plus side some of the bottom tier anker chargers will do 12v.

Plus I think the very new PPS ones should too

Comment by smallmancontrov 1 day ago

Transistors exist. Load switches exist. Looking at Digikey, the expensive ones cost $1 in quantity. I'd pay considerably more than $1 per unit to have this feature that I consider necessary for a minimum viable adapter. Based on these comments, though, TAM is probably tiny.

Comment by Havoc 1 day ago

Think with these low end decoy triggers you’re lucky if it implements standard never mind the optional parts.

You could always request a non optional feature and convert it up/down yourself

Comment by smallmancontrov 1 day ago

Yes, this is one of those "I can't believe I'm considering making it" things. I might actually go forward if I had the slightest confidence I could sell it and amortize my time, but looking at the comments here, who not only didn't understand the problem but didn't understand the problem after having it explained to them -- TAM is tiny, it'll never amortize. Sometimes you just have to scratch an itch, though.

Comment by ianburrell 2 days ago

Those are called trigger boards. I haven't found one with buck converter to make 12V. 12V is in earlier PD standard so lots of chargers support it but you have to check each charger and lots don't say. The guaranteed solution is PPS chargers that have variable voltage.

Comment by s0rce 2 days ago

There are things like this: https://www.adafruit.com/product/5501 haven't used it, trying to find one for my mini pc, mostly so I can use a usb c power bank as a tiny DC ups.

Comment by smallmancontrov 2 days ago

The description explains (in bold, multiple times) that it has the awful behavior I am looking to avoid.

Comment by dotancohen 2 days ago

Actually, that was 5v, not 9!

Comment by userbinator 2 days ago

IMHO this is a classic example of extreme overcomplexity leading to fragility and regulatory capture along with increased opportunities for antiuser hostility. Practically all devices needed nothing more than +/- on a robust barrel jack, but now we have negotiable voltage (with disasterous consequences if there is a bug in the inherently software-driven process --- which will certainly happen) pushing insane amounts of current through a tiny effete connector with barely-visible pins, "authentication" schemes to enforce vendor lock-in under the guise of protection, and entire regions legally mandating this flustercuck.

Comment by mtabini 2 days ago

Can I offer a counterpoint? Much like OG USB put a 5V supply within everyone's reach, USB-PD has made programmable, higher power supplies available to everyone. That's a big deal, because PSUs are an expensive portion of a product, especially for small manufacturers and hobbyists. Having a dedicated standard that supports multiple voltages and currents allows small players to take advantage of the same economies of scale as the largest electronics manufacturers.

Case in point, IKEA will happily sell you a very well built 20W power supply that provides 5, 9, 12, or 15V for less than $5 here in Canada, and you can get a similar price from legitimate Asian distributors, even when buying in limited quantities. If you're working on a small-batch electronic product, that's a boon to your BOM; if you had to go out and source a dedicated barrel-jack PSU with the same capabilities, it'd cost much more, and you don't know what kind of quality you'd be getting.

Where the standard really falls on its face, IMO, is in its opacity. You can get a chip that does the PD negotiation for pennies, but there is no way to inspect the protocol without shelling out thousands for a dedicated analyzer, so when things don't work, it's really hard to troubleshoot the reason.

(Disclaimer: I'm working on an open-source protocol analyzer, so this probably colours my view on the matter a little.)

Comment by mmastrac 2 days ago

The consequences of plugging the wrong voltage or polarity into a barrel jack, most of which are compatible enough, is pretty bad. Ask me how I know.

Comment by userbinator 2 days ago

That's still far simpler and more obvious than the insanity of USB-C. Looking at all the complaints about "noncompliance" makes it much clearer.

Comment by anon7000 1 day ago

Is it? DC barrel plugs look identical to most users. Just like USB C. Only one of them negotiates the correct voltage by default in most cases.

This is a non issue, IMO. Does it depend on the electronics being designed correctly? Sure, but that’s the case for all electronics, and most devices probably build on some widely-available standardized control boards from 3rd parties.

As a user, I’m sooo happy that I can bring a portable battery and a wall charger, and both can recharge every single one of my portable devices. From gaming handhelds to large, powerful laptops, to wireless earbuds, to cameras, to smart watches, to flashlights. All with very different power requirements.

Comment by Schiendelman 2 days ago

This is purely a standards problem. The working group had to say "you don't get the logo unless you do PD" and have logo. They waited a DECADE to do that, which missed the boat, and when they did it they focused on transfer speed and wattage markings instead of a single stamp.

Comment by sysguest 2 days ago

security-wise, usb-c is the worst scenario device I've ever seen -- unless you're Apple, you can't make a security-boundary without infringing patent US11205021B2

for laptops, a bad-actor usb-c cable/charger can do so much more, unless your laptop has AI that can distinguish "is this signal really coming from monitor/keyboard/etc ?" I'd rather have plain-old DC adapters (or usbc to dc)

Comment by v1ne 1 day ago

"USB data blocker" on AliExpress yields you very small adapters that enable you to run USB-PD, but block the data lines.

Comment by pjc50 2 days ago

What are the actual security issues, HID injection?

Comment by Animats 2 days ago

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

Comment by jeffbee 2 days ago

You joke, but this is enough to make recharging an e-bike practical. E.g. https://amplerbikes.com/pages/nova

Comment by theragra 1 day ago

This is my dream. To reverse engineer my bikes charger and create an USB pd to take with me on a self-sustained trips.

Comment by dotancohen 2 days ago

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.

Comment by wongarsu 2 days ago

A full sized European electric kettle is about 2000 watts, but if you limit capacity to a single cup you can get acceptable performance on 200 watt. A USB-C coffee pot or kettle scaled to 0.2 liters (7oz) could work. Would be a great option for travel

Comment by 2 days ago

Comment by Animats 2 days ago

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

Comment by gsich 2 days ago

You sure?

Those regulations go even higher.

https://en.wikipedia.org/wiki/Extra-low_voltage

Comment by exmadscientist 2 days ago

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.

Comment by dotancohen 2 days ago

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.

Comment by seba_dos1 2 days ago

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.

Comment by tredre3 2 days ago

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!

Comment by m463 2 days ago

I remember scoffing years ago at USB powered coffee warmers. Maybe the situation has changed.

Comment by Schiendelman 2 days ago

The Ember cups could have used PD! But the cables would have been more expensive, as would have the power brick (and you would have had bad user experiences plugging into less powerful USB power supplies)

Comment by ksec 2 days ago

I mean my electric Fan and standing lamp are both powered by USB-C.

There are things that shouldn't be powered by USB-C. But there are plenty of sub 100W consumer electronics devices that really should be USB-C. I waited years before Panasonic released their lamdash shavers using USB-C.

Comment by rpaddock 1 day ago

I have found this ST Discovery kit extremely useful in figuring out what my USB-C power sources could actually supply.

"The STM32G071B-DISCO Discovery board is a demonstration and development platform for the STMicroelectronics Arm® Cortex®-M0+ core-based STM32G071RB microcontroller and particularly the USB Type-C™ and Power Delivery controllers.

...

The STM32G071B-DISCO Discovery board discovers and displays USB Type-C™ port capabilities such as data role, power role, VBUS and IBUS monitoring. ..."

https://www.st.com/resource/en/user_manual/dm00496511-stm32g...

Around ~$70 US now. Was around $50 when I bought mine a couple of years ago.

STM32G071B-DISCO at Mouser or Digikey.

Comment by throwaway81523 1 day ago

Madness. USB C doesn't even let you control which way the power goes. Try to charge your phone by plugging in a USBC power bank? Oops, the phone is charging the power bank instead of the other way around. Sometimes you can't even make that stop without a USB-A cable. I can't imagine what kind of fools invented that.

Comment by bar000n 2 days ago

lots of hallucination or should i say misinformation in this article

Comment by infoinlet 2 days ago

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