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Comment by bluGill | Hacker News Reader

USB-C never defined a Y cable and so they never figured out how that would work. If such a cable works anywhere it is either luck, or there is some chip inside that checks for power messages from either end but otherwise looks like a straight through cable. Even then it will be tricky because if the two devices want different voltages from the charger only one can get their way.

I can't blame the USB-C people for not working on this case. It is a lot harder than it seems to make work, and of limited use. Just get a USB-C hub if you need this ability.

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Isn't this exactly what USB-C docks are for?

I've seen plenty of those devices, where you have a female USB-C socket to connect a charger to, a range of other female USB-C, USB-A and other ports for peripherals and a short cable with a male USB-C plug to connect to a laptop. If everything works, the dock will act as a power source for both the peripherals and the laptop, but will act like a hub on the data lines, with the laptop being the host.

I wonder if it would work just the same if you connected a phone instead of a laptop to the "host" cable.

That is what a dock is for. OP wants a simple and cheap cable instead which isn't really possible in the generic sense (though it might work in some limited way)

I've connected my phone to the host cable of a dock before and everything worked. (I didn't try the HDMI output, but sound on the dock just worked)

This is known as a USB Accessory Charging Adapter of which a dock is one form but the old Battery Charging standard also anticipated it being in the form of a cabled adapter:

Battery Charging 1.2:

> An Accessory Charger Adaptor (ACA) is an adaptor which allows a single USB port to be attached to both a charger and another device at the same time.

Figure 3-1 shows the various configurations covered. The third one indicates the intent of having an adapter with data pass through to an accessory while powering from a third port fed by an external USB supply.

These exist today as USB-C splitters.

The docks we have around here at work all use Displaylink chips. So it would work if the phone had the (software) Displaylink driver, no Displayport video capability required on the USB-C port. But I'm guessing that's unlikely.

Hmmm, it occurred to me, I'm sitting in front of a laptop connected to a (power delivery) USB-C dock. So unplugged the laptop and plugged the cable into my phone instead (very basic, Moto G Play 2023). What happened? Almost nothing! The phone reported an audio output device, but did not charge, and the keyboard and mouse plugged into the dock did not get recognized either. Not encouraging.

Well, the Kensington dock at work did not work (for delivering power to the phone and letting keyboard and mouse be used) - in fact it did none of those things. But ordered this cheapie from Ali:

https://vi.aliexpress.com/item/1005007015739540.html

which does claim to work with various smartphones. We'll see.

Would be interested to know that as well. Good luck!

Dunno if anyone stil sees this but.. the gadget came from Ali.

Phone doesn't charge through it. However, my work laptop does. If this thing is plugged in between its USB-C dock and the laptop, it is powered, but the dock is not otherwise seen. So the USB-C socket is a full power delivery passthrough but that's all it is.

The USB-A port does work; a mouse plugged into it is seen by the laptop. Didn't test the HDMI output.

For the phone: Useless. Obviously this phone does not do USB-PD. It just expects the power adapter to deliver 5V. So a limitation with this phone; I'll never be able to simultaneously power it and also get an OTG USB connection.

Heh, if you want a really atrocious USB power violation... Costco sold some extremely bright flashlights (think car headlight bright, and also usable as a self-defense weapon in the spirit of the old D-cell Maglites) before Christmas, that have an USB charge socket. Needless to say they include a charge cable but no charger.

But this thing wants 1.5A at 5V. And doesn't do any power "negotiation" at all, as far as I can see. It happens to work because modern smartphone chargers can do 5V at 2A by default. But plug it into any older charger and the charger immediately shuts down due to overcurrent.

I have one of those USB passthrough voltage/current meter gadgets. Yes, it draws 1.5A. I guess what it should be doing is slow-charge unless it can negotiate for more power. It's a very decent flashlight otherwise.

Oh, it also has two USB-C sockets. A red one for charging, and a black one for using the flashlight's substantial battery as a power bank. I don't know what would happen if you plugged the charger into the wrong socket and don't have the courage to try.

> Oh, it also has two USB-C sockets. A red one for charging, and a black one for using the flashlight's substantial battery as a power bank. I don't know what would happen if you plugged the charger into the wrong socket and don't have the courage to try.

USB-C does a bit of negation before putting our any significant amount of power. There's a "dumb mode" that just uses a pair of half-cent resistors and is fine for up to 3A at 5V, and then the "smart" PD (Power Delivery) mode that does a digital negotiation and can do much higher wattage.

All that is to say that if you plugged the black USB-C into a charging brick it'd probably just fail the negotiation and nothing bad would happen. Both sides would have to be violating the spec for it to be a real hazard.

Annoyingly, some really cheap devices skip out on even the dumb mode resistors to save a penny, and so even though they have USB-C ports, you have to charge them with USB-A to USB-C cables (because USB-A ports always provide power, no negotiation required.)

Those devices are where the cheap Y-cables come in handy, because they usually include the required resistors + give you a USB-A port.

The flashlight comes with an USB A->C charging cable, as do the (low end) smartphones we have (along with USB-A power adapter for the phones). Thus probably no PD negotiation. Right?

A lot of flashlights and cheap gadgets have USB-C port but can only charge from USB-A port. The reason is that they cheaped out on including the resistors that signal legacy USB mode. The USB-C to USB-A cable has the resistors.

The smartphones should have proper USB-C port, I haven't heard of one with charging problems, and included USB-A cable cause cheap.

Aah, yes, the USB-A side always provides power, no negotiation needed for that aspect. There is still supposed to be some level of negotiation before drawing that much current (often just checking resistance, similar to the USB-C "dumb" mode), but obviously the device skipped that also.

No need for weird racism.

American companies like Skullcandy do this too.

Fair enough, edited.

> extremely bright flashlights (think car headlight bright, and also usable as a self-defense weapon in the spirit of the old D-cell Maglites)

Using a device which is mostly lithium ion batteries as a weapon? Even scarier than you expect, if you puncture a battery

First of all these flashlights are very sturdy, and second, if you need a self-defense weapon, I don't think a slight danger of the weapon bursting into flame, post-use, is a high priority concern. The battery pack is a relatively loose fit, slide-out item inside a metal tube. All the charge electronics including connectors are part of it. The flashlight actually comes with an alternative battery pack that takes (a lot of) AA cells.

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