There is a reason for USB-C extensions not to be part of the standard. They can be bothersome in the best case and dangerous in the worst.
So a standard cable needs to be chipped to show its rating to the device, its not that the device can pull what it wants or can get, but the cable itself tells it what it can supply. Extension cables can’t do that, because it doesn’t know what it’s plugged into, and that would be if they even bothered to put a chip in. They instead piggy back off the chip for the main cable. The problem comes when you you have a 240 watt cable hooked up to a cheap 120 watt cable, with the device being told it can push 240, and starts to super heat the extension cable
Brilliant thanks
5 sentences that inexplicably need a 9 minute video to say
Fuck YouTube
This sounds solvable, doesn’t it? Have the extension cable have a chip saying it can do X at maximum, then compare with whatever is to be extended and communicate the minimum of both upstream. Might not become a sleek cable-like design, but would extend the 240W cable with the extender safely staying at 120W
That’s an active extension cable, which is essentially a single port USB hub.
Shouldn’t it be possible to only do the negotiation part and otherwise bridge everything? Not having to do anything high-bandwidth actively should keep the silicon costs down.
Heh heh heh. Wait till you dive into the world of “That $15 cable costs 12c to make.”
Well, the source checks the cable using the CC line which doesn’t go through the cable (VCONN). So source only knows the cable directly plugged in. To make the extension cable visible, the sink would be required to check the cable plugged in using VCONN and then the tell max ampere to the source over the other CC that goes through the cable.
2 Problems:
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Sink devices normally don’t read or can’t read VCONN as far as I know
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No way of detecting if a third cable (extension in the middle) is present and what specs it has
Correct, except for your example. Firstly, 120 watt USB c cables don’t exist, only 60w, 100w, 140w and 240w. And only plugging in a 100w or higher cable into a 60w extension would be dangerous, since it would allow drawing 5 amps on a cable over an extension only designed for 3 amps. However, as soon as your extension is rated for 100w it is completely safe to use with any USB c cable, even those rated for 240w, as those only operate at a higher voltage but still only allow 5 amps max.
I have also never seen an USB C extension cable rated for less than 100w, so this is kind of a moot point. If 60w usb c extensions exist somewhere, they would indeed be dangerous, but I have never come across one
Interesting, I’d never trust any USB cable to push anywhere near 100 watts anyway haha good god, the most I ever do is maybe 20w at 5v.
I’ll keep that in mind when buying cables in the future though this is very useful info!
As a point of reference, Lenovo Thinkpad’s have something of a cult following for their reliability and versatility.
My T490s has a USB-C power supply which provides 45w (20v at 2.25a).
The thing is, when docked it’s not only pulling power through that cable, but also network, USB devices, and providing video for 2x monitors in 1920x1080. It’s kind of astonishing to me how much can be crammed in to one little connector. That said, it’s frustrating trying to find a usb cable that works reliably, because as you’d imagine not all USB-C cables support the same specs.
If you buy a Steam Deck, or the Lenovo laptop I have for work, the only charging options you have are USB C. Their standard chargers put out at least 60 45 W, and they aren’t particularly special. In fact, I’m pretty sure 20 W at 5 V won’t be enough to supply these while in use, so you will either be using battery with long charge times in between, using them with battery-assisted power for longer use times until you hit those long charge times, or using the 60 45 W or more at whatever voltage the chargers provide.
My laptop can do 240W over USB-C, I’m just waiting for a charger that can do it with a modular cable
It has a 240w charger but have you checked to see that it’s using all 240w?
Most laptops use (up to) 120w.
Safety regulations are written in blood. Electrical fires were indeed a problem. It’s why there are rules on how many outlets need to be in a room, how spaced out they need to be (to curtail extension cord usage even when the builders are trying to be cheap and stingy with outlets). It’s the reason why we have breakers and GCFIs and RCBs and AFCIs. It’s the reason why we have electrical certification bodies like UL which won’t certify your cable or appliance if the cords are too thin.
There’s a lot of smart stuff we do behind the scenes to make dumb cords safe because even smart people make dumb mistakes.
“Dumb” power cords have thicker gauge wire than USB-C cables and much larger contacts.
