Hacker News Reader

Comment by error503 | Hacker News Reader

Without USB-PD, existing phones will already limit their charge current, and Android at least will say 'charging slowly'.

The place to enforce USB-PD is at the source, which is what is happening in your described scenario.

Yes, sinks should definitely honour their power contracts, but phones generally already do this (they need to work with 500mA, 2A, and potential faster chargers without overloading them), and don't usually have power-sucking peripherals attached that will mess up their actual draw.

> Not too big of an issue at lower loads, but it will crash if I plug a hard drive in its USB port.

This hard drive probably violates USB spec, as most spinning disks do.

View on HN

> The place to enforce USB-PD is at the source, which is what is happening in your described scenario.

Which source? The charger or the device? Because either could be at fault.

> This hard drive probably violates USB spec, as most spinning disks do.

It's a SSD from a well-known manufacturer, with a power draw of less than 4W at full load.

> Which source? The charger or the device? Because either could be at fault.

Any device acting as a power source - but you need PD for this so you can create power contracts that are compatible with the root power source, and you're not describing a PD situation, so this is not possible.

Probably your router does limit downstream power, but due to many years of devices ignoring the 500mA limit, these limits are usually very liberal so as to avoid users complaining that the USB port doesn't work with device X. PD helps with this by establishing a way for sources and sinks to negotiate a clear power delivery contract that the source can be strict about limiting.

4W is more than non-PD USB can supply, so the fact that it doesn't work is not that surprising.

> 4W is more than non-PD USB can supply, so the fact that it doesn't work is not that surprising.

And still, it is an USB-C port with the label "storage" in it.

> ... these limits are usually very liberal so as to avoid users complaining that the USB port doesn't work with device X

It seems that there is an actual problem, then.

> It seems that there is an actual problem, then.

There was, and as a result almost no vendor actually strictly followed the standards prior to USB-PD providing a way for this to be managed reasonably and deliver more than 2.5W.

The modern standards are fine. As usual, implementation quality varies.

Reply on news.ycombinator.com