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I have a Pi 4 connected to a Viewsonic Touchscreen monitor.

The monitor has a USB C output that the monitor user manual shows being used to power a laptop. I am trying to use this USB C output (nominally 57W from memory) to power the Pi and it does work but not well. The Pi has a couple of goes before it boots and then strange things happen like data being sent to the network being only intermittently sent.

I have seen other posts talking about powering the Pi from USB-C powerbanks etc. I am wondering whether the Pi correctly negotiates for the correct voltage and current? I also saw cables mentioned as possible problems but they seemed to imply that it would not work at all with the wrong cable ??

Suggestions please.

DG

David G
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2 Answers2

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The Pi only operates from 5V.

If it doesn't work it is likely the power supply can not supply sufficient current or more likely that the cable is inadequate. The official Pi supply has an inbuilt cable which uses heavier gauge wire than most cables.

The original Pi4 had a design flaw and was reported not to work with Emark cables.

Do you get a low voltage warning?

Milliways
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  • I can't see if there is a low voltage warning as the Pi boots into an app and I can't SSH into it. – David G Nov 24 '23 at 04:43
  • You claim to be using a monitor power supply so why don't you look at the monitor screen? You can also look at the logs to see any history of undervoltage. – Milliways Nov 24 '23 at 05:37
  • vcgencmd get_throttled will show if undervoltage has occurred. – Milliways Nov 24 '23 at 23:18
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There's no negotiation from the RPi side; the USB source either supplies the needed power - or it doesn't. If the monitor is actually capable of supplying 57W at 5V (±) then it should work fine... but I suspect that it does not - here's why:

USB-C power sources have the capability to supply high power, but they do so at output voltages up to about 20 volts! The RPi - although it has a USB-C connector - is unable to handle this part of the USB-C specifications. In other words, the RPi needs 5V - and only 5V - from the supply.

Much of this was covered in an old answer from 2019. I won't re-hash all the details here, but you may wish to read it. But the bottom line for your Viewsonic monitor is that you'll need to review the specs to see what its current capacity is for 5V, and you should use a proper USB-C power cable to connect your RPi (no data).

Finally, the old answer tells you which type of power cable (e-Marked vs non-e-Marked) you need depending upon the model of your RPi 4B.

Seamus
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