Can I power a RPI4 from the duet 3 mini?

[nikscha]

I want to power the pi from the duet because I want to have as few wires as possible and because of how the ribbon cable positions the pi, the micro USB cable would be in an awkward position.

I understand that the 5V regulator on the duet is not sufficient to power the pi, but what if I feed 5V from an external source via the PS_ON / 5V_IN header?

[dc42]

You cannot power the Pi from the Duet 3 Mini. The ribbon cable connector does not include a connection for 5V power.

[Serbitar]

@dc42 It must do? The Duet Mini 3 has a jumper to select the SBC as power source.

I haven't tried but did theorise that I could feed 5v in externally, bridge all three pins of the +5 Source jumper and add jumper to "internal 5v disable" jumper.

More recently I have created a custom cable for the SBC interface so i can fee the SBC and Duet Mini 3 separately from the same external supply.

[nikscha]

@dc42 the ribbon cable definitely carries 5V from the pi to the mini.
@serbitar I had the same Idea.
The 5V_SBC pin is connected to 5V on the RPI.
When I power the mini via the PSon header, there will be 5V on 5V_EXT_IN.
With a "triple jumper" I can then connect that to 5V_SEL and 5V_SBC at the same time, therefore applying 5V to both the duet and the pi (int 5v disable is fitted)
In the same manner I can connect a normal jumper over 5V_SEL and 5V_SBC and NOT fit the int_5V_disable jumper to power the pi via the 5v regulator (which will probably not be powerful enough).

[nikscha]

I did some testing and I can confirm that powering the Pi from the duet mini is possible.

This is my setup:

• 5v/GND from PSU into EXT_5V_IN/GND
• jmper on int_5v_diable
• jumper on 5V_EXT_IN and 5V_SEL
• F2F dupont cable from EXT_5V_IN (neopixel) to 5V_SBC

Pi is booting up fine and I can access DWC but I get a low voltage warning from the Pi

[CNCModeller]

@nikscha said in Can I power a RPI4 from the duet 3 mini?:

Pi is booting up fine and I can access DWC but I get a low voltage warning from the Pi

I believe that's because that connection on the Duet board isn't rated to output enough current to run the Pi so you're getting a voltage drop. You're probably going to kill the Duet over time if you do. Hence why @dc42 said it wasn't possible.

[nikscha]

@cncmodeller I doubt it actually.
I get continuity from EXT_5V_IN right to the Pi's 5v pin. So as long as there's no trace that can't handle the current requirements of the Pi, the duet should be fine.
I suspect the low voltage warning was due to my psu setup:
I had my PSU set to 4.9v and a current limit of 2A

[CNCModeller]

@nikscha

Hey all I'm saying is that @dc42 designed this thing so personally I'd expect he knows what's the score.

If you're not getting normal behaviour from your Pi I expect there is a reason. Continuity doesn't mean it's designed to power external devices.

But feel free to do what ever you think is right, it's your equipment, and nothing to do with me what you do with it.

Hope it all goes well

[dc42]

it seems that the 5V regulator on the Raspberry Pi isn't a true Low Drop regulator, because the RPi prefers 5.2V input rather than 5V.