USB PD is also a shit show. You might want to read this:
goughlui.com/…/tested-usb-c-barrel-connector-adap…
Which shows those USB PD negotiations can get dicey. It chooses voltages thought to be close enough to what’s requested.
I’ve run into a nasty problem where a USB-C appliance needed 9v. Says in the manual something like “only use Kenwood power supplies on this device”. I thought, fuck that, USB PD is a standard for a reason. I’m not going to blow money on a proprietary OEM Kenwood USB-C PSU. Then found that many power supplies actually skip 9v. The USB PD standard makes some voltage steps optional, and some mandatory. IIRC, 9v was one of the required ones, yet it was easy to find USB-C power supplies that skipped 9v but offered 12v (or 15v, I forget). And yet 12v or 15v was one of the voltage steps that’s optional.
So I have an adsptrt that goes from battel to USB-C
That’s joy part of USB spec as there’s no way to communcate requirements through the barrel. Hard to blame USB for when we side-step it’s design.
I do stuff like this too, but only for devices that just need power, nothing like a laptop or with circuitry that could get fried by the wrong voltage.
That’s no part of USB spec
Do you mean the USB PD spec? It does not violate the USB spec which sets a default voltage of 5v. The adapter /would/ violate the USB PD spec if it were to claim to be USB PD compliant. But the shit-show we have is that USB-C does not imply USB PD. And so the market is full of USB-C things that are not USB PD. And often they do not claim to be USB PD as consumers are not wise enough to demand it.
Note as well the adapter I mentioned is quite dumb – just hardwires pins for the situation that the appliance expects 5v without negotiation. But it would be possible to implement a USB PD-compliant adaptor with the smarts to handshake, which would then refuse to complete the handshake in the event that the voltage supplied is not that requested. Of course it would be a bit strange to put that much sophistication into it which would likely drive the cost to that of a whole compliant PSU anyway (thus defeating the purpose). But notice the opposite has been done, whereby the adapter negotiates a voltage on behalf of a barrel device.
as there’s no way to communcate requirements through the barrel.
IIRC, it’s disputed whether the hanshake negotiation is needed for 5v. Some appliances expect to do a handshake /no matter what/, and some 5v appliances are designed to skip the negotiation entirely. If you are in the camp that says even 5v must have a handshake negotiation, then you would condemn the simple barrel to usb-c adapter (but perhaps not one that is only for a fixed input and the circuitry to do the negotiation).
Hard to blame USB for when we side-step it’s design.
The blame was not pin-pointed. I pointed out a shit show in the marketplace. There are bits of the standard you can blame, and you can also blame market actors. You can probably also blame regulators for not preventing the shit show that I described.
I’m getting the sense from your comments that you think that USB-PD will deliver a higher voltage than requested. This is not accurate. A device can request any of the voltages specified by PD, and the power supply will supply that voltage if it is capable of doing so. If not, it will provide 5V. It’s very possible to get a sippy that won’t power your device, but a working, PD-compliant power supply will not damage a working, PD-compliant device.
Obviously, if you get a barrel jack adapter that requests 20V and then plug it into a 5V device, you’re going to let the magic smoke out, but that’s because barrel jacks don’t do negotiation. The power supply correctly supplies 20V as requested, and then you plug that 20V into the wrong thing.
I’m getting the sense from your comments that you think that USB-PD will deliver a higher voltage than requested. This is not accurate. A device can request any of the voltages specified by PD, and the power supply will supply that voltage if it is capable of doing so. If not, it will provide 5V. It’s very possible to get a sippy that won’t power your device, but a working, PD-compliant power supply will not damage a working, PD-compliant device.
That’s not true. See the experiment I linked.
Obviously, if you get a barrel jack adapter that requests 20V and then plug it into a 5V device, you’re going to let the magic smoke out, but that’s because barrel jacks don’t do negotiation. The power supply correctly supplies 20V as requested, and then you plug that 20V into the wrong thing.
Of course. Not sure what point you’re trying to make here but the conversation was about whether the barrel adapter is compliant with the standards. Not whether you can misuse it.
If 19.5v is requested, 20v is supplied.
You’re misreading the blog post. That adapter has 19.5V written on it, but it requests 20V. 19.5V is not a PD voltage.
You can have a USB→barrel and you can have a barrel→USB.
The latter is pretty much impossible to make to spec, because it can’t negotiate voltage. A barrel jack is single-voltage by necessity.
The interesting case is what I described, when the appliance and PSU are compatible in terms of voltage but still fail because of the protocol.
Respectfully, I’m going to have to disagree. It’s much more interesting when it catches fire, and I’d rather have a protocol that sometimes doesn’t operate in order to avoid the excitement of one that sometimes explodes
Also consider that a 20v barrel PSU could feed a dumb usb-c adapter which then fries a 5v device.
No matter what charging standard you use, some idiot could cut off the end, wire it to a stun gun, and send 100,000V into your phone. That doesn’t make the standard bad, it makes the adapter bad.
And in both situations (usb→barrel and barrel→usb), it’s not foolproof.
If you do it correctly, a USB power supply being adapted to a barrel jack won’t destroy any device that can tolerate 5V. It may not operate the device, but as long as nothing breaks, I’d consider it as foolproof as anything reasonably can be.
Countless consumers cannot handle the voltage matching task so if the plugs fit, they will try it.
That’s just how electricity works. You can get 5V devices that use 5.5x2.5 barrel jacks and you can get 20V 5.5x2.5 power supplies. You can get C13 leads that connect to 240V wall outlets and you can get C14 devices that only accept 100V. If someone plugged things in without reading before USB, they broke things and started fires. PD simply doing nothing when incompatible devices are connected is a massive upgrade over that, even if it can be frustrating sometimes.
You’re misreading the blog post. That adapter has 19.5V written on it, but it requests 20V. 19.5V is not a PD voltage.
That is not what the blog post said. We know the /result/ is 20v, not what was requested. It’s a lie and abuse to print 19.5v on an adaptor that is actually just requesting 20v. It’s certainly /possible/ that is what is happening, which obviously proves my point nonetheless. It’s yet another demonstration of the USB PD shitshow. Either way in fact. Whether the negotiation is a lie, or whether the source is saying “close enough, will send 20v”, it’s a shitshow either way.
But now it’s worse because consumers who know how to pay attention to voltage are getting a product that’s not what they signed up for.
The latter is pretty much impossible to make to spec, because it can’t negotiate voltage. A barrel jack is single-voltage by necessity.
First of all, the adapters exist. Not impossible. If you meant to say a smart negotiating one is impossible, that’s not true either. It could detect whatever the barrel passes and use that result to negotiate only for that available voltage. It could even have a voltage converter that supplies voltages that differ from the source. In fact I have a DC-DC adaptor. You probably have one and don’t know it. A USB charger that plugs into a car’s cigarette lighter converts 12v to 5v. I have one that has a variety of tips and a range of voltages. Detecting the source voltage may not be cheap, but not impossible. It would also be possible to have a cheap manual switch to specify input voltage.
Respectfully, I’m going to have to disagree. It’s much more interesting when it catches fire, and I’d rather have a protocol that sometimes doesn’t operate in order to avoid the excitement of one that sometimes explodes
If you find explosions interesting, you can go play with fireworks or watch war movies. It’s not academically interesting that tech illiterate consumers find countless ways to shoot themselves in the foot. When engineers — who /should/ know what they are doing, push a shitty standard that burns even consumers who have the basic knowledge to match devices, that’s academically interesting because it’s people we expect to be smart fucking up. When a whole industry fucks up, that’s academically interesting. I cannot charge a 5v bicycle light using a USB PD spec’d PSU because the industry fucked up on the meaning of “default”.
No matter what charging standard you use, some idiot could cut off the end, wire it to a stun gun, and send 100,000V into your phone. That doesn’t make the standard bad, it makes the adapter bad.
Dumb consumers are not in short supply. It used to be that only tech-illiterate consumers were getting burnt. Which created an incentive for consumers to gain knowledge. The nannying attempt at a remedy has enabled informed consumers to get burnt. At the same time, it dumbs down society. When expert consumers can get burnt, of course it reflects a poor standard.
And poor practices. A good standard anticipates what the market will do. They did not anticipate different product makers having a different interpretation of “default”.
but as long as nothing breaks, I’d consider it as foolproof as anything reasonably can be.
It’s now clear why you have no problems with the standard – you have a low expectation. The Lenovo PSU that supports 5v /should/ be able to charge a 5v appliance. But they botched the negotiation and absence of it.
That’s just how electricity works.
I was describing how /people/ work.
cmnybo@discuss.tchncs.de 3 weeks ago
12V is optional now. It was part of PD revision 1.0 and dropped in later revisions, but many chargers still support it. 9V has been required since PD rev 2.0.
With the device that uses the 9V only USB adapter, I would either glue the plug in or replace it with something else. Its too easy to accidentally fry something with that.