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I never knew that USB-C extensions are not allowed for a reason
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this post was submitted on 26 Dec 2024
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Anybody care to sum this up for people who can’t watch videos?
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.
Yes, and such cables already exist, like this splitter cable:
https://www.amazon.de/dp/B0CRZ6JJ6D (not an affiliate link)
It's not an extension cable, but it does exactly what you are suggesting. It gets the available PD profiles from the charger and then intelligently negotiates a profile that will work best to split the power to the 2 devices connected to it. The charger thinks it's just connected to 1 device, and the connected devices think they are directly connected to a charger.
Doing the same for with a USB C extension would be trivial, but it's probably hard to market such a cable when passive USB c extension cables are available at a fraction of the cost, even if those aren't compliant to the USB standard
I wish there was a clearer explanation or nomenclature for this. With things like cables and converters everything always seems to have a black box layer.
I don’t understand why there are so many PD profiles either. Maybe Cat-1 USB-C, Cat-2 USB-C, etc? Maybe just having a smaller set of voltage-defined profiles that have a safe maximum current rating? Maybe that’s already how it is? I don’t know
There are technical reasons for why so many PD profiles exist.
In fact they were not enough, which is why the USB Standard was extended with the "PPS" extension recently, which let's the attached device freely choose a voltage between 3V and 21V in steps of 20mv, and more importantly it let's the device freely change this voltage without interrupting the charge process. This change makes it possible for devices to bypass their own but in charging electronics and just directly forward the voltage coming from the charger to the device, improving efficiency and significantly decreasing how much the device hears up during charging
Sadly PPS is not found on many devices or chargers yet, and makes the already complicated USB C charging situation even more complicated for consumers
Heh heh heh. Wait till you dive into the world of "That $15 cable costs 12c to make."
Getting $30 cables for $3 with my employee discount was almost the only good thing about working for Best Buy in the early 2000s.
I'm right now in China and those cables cost $0.50 shipped to your address, so not surprised
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:
Sink devices normally don’t read or can’t read VCONN as far as I know
No way of detecting if a third cable (extension in the middle) is present and what specs it has
Soon on Amazon..
1m USB-C CABLE HEATER!! 0.99c
($5.99 shipping)
Pretty much this, thanks for the summary
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
Going to take a wild guess and say the same reason you shouldn’t chain extension cords. USB can carry over 200w these days.
what if I don't know that either
It all depends on current draw vs wire size over distance.
No, that's not the reason at all. The actual reason is a phenomenon called "loop impedance", which increases exponentially with each additional plug connection you chain together, regardless of the wire guage and distance of the extension
Too high loop impedance can cause your RCD to no longer trigger if you accidentally touch an exposed live connection, which is a major electrocution risk
Are you referring to AS/NZS 3000? I've never come across that here in the states, that's some interesting reading and makes perfect sense.
On the practical side without engineering calculations, daisychaining extension cords will simply exacerbate voltage drop, which coupled with increased line resistance, will just cause increased current draw and increased thermal dissipation on the cord (those cords everyone's dad has where the outer jacket is shrunk to hell against the internal wires), and poor reactance of (especially motor driven) equipment. This can be alleviated by using thicker cords (eg #10), but it still has limitations over excessive distance. A small battery charger will probably continue to work, whereas a table saw will have problems.
On the safety side, even sticking your finger on the load terminal of a 20a breaker will not trip it, even barefoot, as the human body doesn't draw enough current, it just zaps the hell out of you. OCPDs are typically designed for system and equipment protection. GFCIs are more effective at protecting a person, but only if the current deviates to a different ground path. As far as I can tell from preliminary reading, the purpose of calculating loop impedance is determining the effectiveness of the grounding (earthing) conductor in relation to distance from the actual transformer. In a real world scenario, this is more going to be say if a cord were to be cut or equipment faults to ground, and whether the impedance exceeds the physical limitations of the wire to trip the breaker (or fuse).
Chaining regular extension cords isn't a problem by itself, connecting too many things in parallel and exceeding the rated max is a problem (and chaining extension cords "just" increase the risk that ordinary people will decide to connect more than they should, especially because the lowest rated cable in the chain sets the total limit)
The issue of chaining extension cords is that you can physically plug a 10 amp extension cord into a 30 amp cord. If you don't know what amps the device will pull, the 10 amp cord can overheat.
It's an almost identical problem to USB c.
Why in the everloving would your electrical code allow sales of extension cords that can't withstand the whole of the plug/socket rating. If it's an adapter from a higher amperage plug to lower amperage socket you need a fuse.
That's just rephrasing what I said. You can plug in too much for a single extension cord even if there's no chaining. A chain "just" increase the risk.
Yes but I was emphasizing the parallels to the USB c problem.
In USBC if you use a 200 watt cable that has 200 watts going through it and then extend it with a 15 watt USB c cable, the 15 watt cable will over heat.
If you plug a 30 amp load into a 30 amp cable and then extend it with a 15 amp extension cord, you will get overheating on the 15 amp extension.
You could also just plug in the 10 amp cord and plug the device into it. The chaining doesn't change anything here.
Yeah, I think in this case there's a lot more tiny conductors sharing what can add up to pretty high current loads on PD connections. Adding extra connectors adding resistance to low (5-20v) voltage high current connections is adding an extra failure point and increasing resistance on the whole cable run.
Not inherently unsafe, but just not a good idea to promote because you know someone will try to run a 200w charging cable for 30m with like 5 connected cables.
This is what AI says about this video:
As always AI doesn't quite get it. One of the main points is that it could catch on fire and burn down your house. Plus you'll run into other problems as well. You're not supposed to buy extensions for USB. Buy a longer cable instead.
You're a bold one. Lemmy hates videos and AI both.
I asked the AI if it was wrong or you were wrong. It said you were wrong.
Who am I to believe?
I'm sick of stuff that should be ~2 paragraphs of text being a video. I do not want to watch a person or hear a narrator, I interpret written information much more effectively, and being text I can retain significant portions of the document as necessary.
The AI got most of it vaguely right, but unsurprisingly a lot seems to go above its head. Kinda like reading a shitty tech journalist writing about something they don't understand at all.
The risk isn't usually the device you connect a bad cable to (they have internal limiters), it's the cable itself. You can easily overload a cable if the extension cord can't signal the lower limit if it's own rating and the other cable's rating.
The USB 2 part is also misleading.
Extensions aren't part of the official spec, so they aren't actually certified as proper USB-C.
Same risks as any other janky no-name gear you see online, even if it SAYS it's rated for a specific throughput or power rating, that may not be the case.