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I never knew that USB-C extensions are not allowed for a reason (www.youtube.com)

submitted 3 months ago by quiescentcurrent@discuss.tchncs.de to c/technology@lemmy.world

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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.

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[-] MargotRobbie@lemmy.world 199 points 3 months ago

If you want a more detailed explanation, USB-C is a small connector that was designed primarily for data transfer, extended power range delivery (240w) was essentially hacked on to the standard. Electricity arcing between the contacts on the connector is the biggest challenge with this hack, since the contacts are small and very close together, which could burn out the circuit board and start fires. For EPR to work safely, there needs to be a lot of extra components on the circuit board/female connector side, which there simply isn't enough space for on an f2m extension cable.

As for why USB-C cables are so short, it's simply a matter of physics, carrying high speed data over larger distances would result in higher losses and requires thicker conductors and more shielding, which is why you don't see USB4 Gen3 cables over 1 meter unless they are optical, and longer "charging cables" are only rated at USB 2.0 speeds, because more often than not they don't even have the USB 3.x data pins on their connector.

[-] Agent641@lemmy.world 54 points 3 months ago

You are a brilliant woman of many talents, Margot Robbie!

[-] MargotRobbie@lemmy.world 37 points 3 months ago

That's esteemed Academy Award nominated character actress Margot Robbie to you!

Also, thank you.

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[-] rjek@feddit.uk 11 points 3 months ago

I don't seem to be able to upvote this twice.

[-] MargotRobbie@lemmy.world 20 points 3 months ago

You could always buy more copies of "Barbie" on Blu-ray for Christmas.

Just saying.

[-] gazby@lemmy.dbzer0.com 5 points 3 months ago

Absolute gold 🤣

[-] narc0tic_bird@lemm.ee 7 points 3 months ago

I have this cable: https://www.spigen.com/products/arcwire-usb-c-to-usb-c-cable-pb2202

It's 2 meters long, 240 watts and supports Thunderbolt 4/USB 4 (40 gbps).

I couldn't test the 240 watts charging as I don't have any device pulling more than 100 watts, but the Thunderbolt 4 part definitely works.

Apple sells a 3 meter Thunderbolt 4 cable (albeit limited to 100 watts of power) that isn't optical either (I think there's some special circuitry in the plugs though).

[-] MargotRobbie@lemmy.world 6 points 3 months ago

You're right. Those are active cables which I forgot to mention earlier that have special circuits that amplify signals, but are also a lot more expensive as a result.

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[-] NobodyElse@sh.itjust.works 180 points 3 months ago

Anybody care to sum this up for people who can’t watch videos?

[-] WraithGear@lemmy.world 268 points 3 months ago* (last edited 3 months ago)

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

[-] Mr_Blott@feddit.uk 38 points 3 months ago

Brilliant thanks

5 sentences that inexplicably need a 9 minute video to say

Fuck YouTube

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[-] TheChargedCreeper864@lemmy.ml 36 points 3 months ago

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

[-] Natanael@slrpnk.net 78 points 3 months ago

That's an active extension cable, which is essentially a single port USB hub.

[-] barsoap@lemm.ee 7 points 3 months ago

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.

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[-] fmstrat@lemmy.nowsci.com 27 points 3 months ago

Heh heh heh. Wait till you dive into the world of "That $15 cable costs 12c to make."

[-] PlasticExistence@lemmy.world 9 points 3 months ago

Getting $30 cables for $3 with my employee discount was almost the only good thing about working for Best Buy in the early 2000s.

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[-] FourPacketsOfPeanuts@lemmy.world 31 points 3 months ago

Soon on Amazon..

1m USB-C CABLE HEATER!! 0.99c

($5.99 shipping)

[-] quiescentcurrent@discuss.tchncs.de 12 points 3 months ago

Pretty much this, thanks for the summary

[-] dan1101@lemm.ee 12 points 3 months ago

Well I'm glad I know that now.

[-] Anivia@feddit.org 6 points 3 months ago* (last edited 3 months ago)

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

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[-] deegeese@sopuli.xyz 23 points 3 months ago* (last edited 3 months ago)

Going to take a wild guess and say the same reason you shouldn’t chain extension cords. USB can carry over 200w these days.

[-] lowleveldata@programming.dev 23 points 3 months ago

the same reason you shouldn’t chain extension cords.

what if I don't know that either

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[-] Natanael@slrpnk.net 14 points 3 months ago* (last edited 3 months ago)

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)

[-] Blue_Morpho@lemmy.world 8 points 3 months ago

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.

[-] barsoap@lemm.ee 8 points 3 months ago

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.

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[-] jordanlund@lemmy.world 7 points 3 months ago

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.

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[-] dual_sport_dork@lemmy.world 48 points 3 months ago* (last edited 3 months ago)

Technically extension cables were not part of the original USB spec, either, but that did not prevent oodles of them from appearing pretty much instantly. They solved a problem, there was a need, and thus they happened.

I.e. there never was supposed to be any such thing as a passive male USB-A to female USB-A cable, and yet pretty much every little MP3 player from 2001 to about 2005 came with one regardless.

[-] asbestos@lemmy.world 24 points 3 months ago

I never wondered about this, but it makes sense now. Off topic but man, the dry mouth noises he makes inbetween sentences are driving me crazy…

[-] Gormadt@lemmy.blahaj.zone 8 points 3 months ago

Yeah after looking into it it totally makes sense to me.

Off topic but you user name is the bestos.

[-] BombOmOm@lemmy.world 17 points 3 months ago

Seems negligent to not include extension cables in the spec. Lots of hubs have too short of cables, or one needs to expose a plug somewhere other than where the PC is.

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[-] AnUnusualRelic@lemmy.world 13 points 3 months ago

I'll have you know that I've been using a 2m extension on my deck power supply for a while and haven't had any fires to speak of. Almost none actually.

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[-] Magister@lemmy.world 6 points 3 months ago

I have a 240W extension from AliExpress, used with a 120W power for my laptop, it never gets hot even when using 100+W

[-] jayandp@sh.itjust.works 8 points 3 months ago

Because you made sure the cable is rated for more than what you're using it for. The problem is when somebody doesn't do that. A 60W cable hooked up to a 120W power supply, for example.

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this post was submitted on 26 Dec 2024

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