RPi5 low current message

[Tim ORourke]

I used a USB C pigtail and connected to 10 amp 5V supply.

I get the message that the supply current may not be enough for added accessories.

How does the RPi5 how much current is available?

Tim W4YN

[Paulh002]

I think it measures the voltage.

Here a script to check voltage and temperature throttling

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[dacooley]

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On October 28, 2025, at 06:15, Paulh002 <paul.hol...@gmail.com> wrote:

The Pi5 looks at the USB-C to see if it supports PD (Power Delivery).   They use resistors across several of the wires in the cable to let devices sense what is available.  A standard USB-C cable doesn't have equal those resistors, so the pi defaults to no PD.  You can override that by editing the /boot/firmware/config.txt and adding the line:

usb_max_current_enable=1

You will still get the warning because it doesn't see the PD resistors, but this forces the Pi to allow full current to the USB ports

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[Paulh002]

This setting is used for enabling USB boot. If you use a non standard psu this will allow USB boot.

My experience (with pi4) that under voltage message was related to the amount of ripple or voltage drop of the PSU.

I wanted to use a linear PSU but it was not fast enough to regulate the current increase of the pi4.

The PI5 is even worse, it needs a very stable psu.

At least that is my experience, 

As far as I know the resistors are at the PI side to instruct the PSU. The Pi5 is not a PD device like a laptop.

 

[David Cooley]

There is actually a very good explanation on the raspberry pi web site. It does support PD and that is how it senses a proper power supply that can deliver 5 amps or more.  This is different than the low voltage error message

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[Paulh002]

Did not know that, but it uses resistors not a PD chip?

[Paulh002]

It does support PD, thats then different compared to the PI4.

On Tue, 28 Oct 2025 at 15:15, David Cooley <daco...@gmail.com> wrote:

[Tim ORourke]

I did some research also, that is correct in that RPi5 uses C PD to determine if supply can supply 5 amps.

I can't   edit config says I don't have permission :(

Tim W4YN

[David Cooley]

Add sudo before your editor command

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[Joey G. (Bonehead)]

Does that effect m.2 drives and hats?  I had issues early on getting a m.2 working and most fixes I saw included turning on USB power boost. 

[David Cooley]

Not unless its connected  via the USB port

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[Paulh002]

What is a bit strange, that there are almost no PD USB power supplies that support 5V 5A, it is all 5v 3A.

Maybe someone knows a PSU that does support this other than the Pi PSU

[Tim ORourke]

The 45 Watt Raspberry supply is only one I have found that has PD and works fine.

Tim