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by ProllyInfamous
42 days ago
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My lay understanding is that USB-C PowerDelivery isn't even initiated until comms have established the supported wattage? ...or perhaps some very low 5W USB-A-like amount. On sudden disconnect, I presume you're talking about a debouncer (RC) circuit? ---- The concern I have is less about initial arcing (i.e. intentional [dis]connections), and more about long-term sustained powerdraw (I have seen soooooo many melted neutral terminals on 120V receptacles) on a loose connection. Connections become loose for a variety of reasons (including but not limited to bad installation), particularly on thermal throttlers (e.g. small wires, corrosion, cycling). Does low voltage world have the same 80% derating as insidewireman-land (NEC/AHJ)? i.e. does a 240W PD USB-C allow continues 240W delivery (by protocol/standard/regulator), or is it neutered to 180W for "long-term loads" == 3+hr runtime (e.g. a computer display), with only ≥181W-peaking allowed..? I just cannot see how such a small connector/cable can deliver sustained 240W, in the realworld that I've lived in. |
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Correct that this is only a worry about disconnects.
> The concern I have is less about initial arcing (i.e. intentional [dis]connections), and more about long-term sustained powerdraw
I think devices usually monitor voltage to make sure there isn't too much loss, and you're probably not going to get enough loose pins at the same time to see dramatic issues.
It's a valid concern, but it's a concern you'd see on almost any type of plug, isn't it?
> Does low voltage world have the same 80% derating as insidewireman-land (NEC/AHJ)? i.e. does a 240W PD USB-C allow continues 240W delivery (by protocol/standard/regulator), or is it neutered to 180W for "long-term loads" == 3+hr runtime (e.g. a computer display), with only ≥181W-peaking allowed..?
They're not worried about heating that takes more than 3 hours, so that specific kind of derating isn't part of the spec.
The 3 or 5 amp limit is designed around continuous load.
> I just cannot see how such a small connector/cable can deliver sustained 240W, in the realworld that I've lived in.
Well for sustained current we're worried about the amps, right? You get the same resistance and heat in the plug regardless of voltage.
Before USB C, we were putting 3 amps over a single pin each way in a USB Micro connector. Now with USB C we're putting 5 amps over 4 pins each way, with the new pins almost as big as the old pins.