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So basically my Alienware R4 17" 2017 model has USB C ports. I think USB C ports are a standard and operate at 20 volts, 5 amps, and 100 watts for power and charging.

I have a Pi 3 and Pie 3 Model B+. Is it possible to power and use serial communication from a USB C port? (I am using a USB C to USB adaptor on that port).

In this situation which device would govern the power delivery? Because on this below article they state too much power draw can fry the motherboard of the laptop (source).

USB-C cables are playing Russian Roulette with your laptop (TheVerge.com)

Josh Mustillo
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2 Answers2

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The USB sockets on the laptop/PC are typically designed to provide power to low power devices such as keyboard, mice, USB WiFi/BT dongles or communicate with externally powered devices like USB hubs, printers etc.

While the USB standard might support the limits you indicate, expecting the laptop to deliver on entire range that might not work in all cases (the current/power requirements are negotiated when the USB device is plugged in and gets enumerated).

The RPI 3B/3B+ requires 5V/2.5A or better which might be border or exceed the specs what typical laptops connectors are designed for.

As long as you don't plug anything power hungry into the RPi's USB sockets, you might not fry your laptop and/or RPi but that would be tempting fate (IMO).

The recommended way to power the RPi is to

OR

  • Use one of 5V/2.5+A capable wall wart with either a micro USB connector

OR

  • Or use an externally powered USB hub.

Also using a thick USB cable would be best to carry the required current to the RPI.

You can then use a USB to TTL adapter to connect to PC.

Shreyas Murali
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  • Ahh appreciate it, yeah I think it might just be best to power it with a wall adaptor and communicate to it with serial connection. – Josh Mustillo Jun 01 '18 at 02:57
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TL;DR:

If you power your Raspberry Pi from your laptop using something like a USB-C to USB hub you will not fry your Raspberry Pi

In response to this part of your question:

In this situation which device would govern the power delivery?

Every device that supports USB-C will have sort of a descriptor table of what voltage and current it can both sink (take in) and supply (give out).

For example, My phone can sink either 5V @ 0.5 - 2A or 9V @ 1A, It can supply 5V @ 0.1A. When my phone is attached to a USB-C capable power plug the phone and the power plug will negotiate with each other about what will work best.

I just looked up a USB-C power brick on Amazon and it advertise this:

"...Charge faster, power delivery fast charge your MacBook, laptop or cellphone at the adjustable voltage and current 5V/ 9V/ 12V/ 15V/ 20.3V/ 3A, or 5V/ 2.4A, this USB C..."

If my phone were to be plugged into this device it would interrogate the power brick and find that it can supply 9V @ 3A and then request 9V @ 1A. If your laptop, that can accept 20V @ 5A, were to be plugged into this device it would request the maximum of 20V @ 3A.

Unfortunately all the pre USB-C cables cannot negotiate power this way so if you ever have a USB-C to a pre USB-C cable the maximum that will be supplied is 5V @ 0.5A (2.5W). Unfortunately, this isn't enough to power the Raspberry Pi and any devices attached to the Raspberry Pi's USB ports (which should all be able to supply 5V @ 0.1A).

Dave
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