How big a 5v power supply needed for Duet 3 and RPI4?

A Former User

here is a pic of the Rpi-4 GPIO pin out if you need it

A Former User

if i'm not mistaken that would put a diode drop in the path of the Pi, but if you can account for that then why not; I'd still prefer to have the Pi running if the Duet is disconnected, thus custom wiring.

Luke'sLaboratory

I use a 24V ATX supply to power my D3 + SBC setup, and wound up just directly soldering the 5v rails to the power in on the RPI and letting the duet power itself. I power USB devices from the PI, so I couldn't use the "only" 3A 5v Standby rails, which would allow me to turn off the duet w/out turning off the pi digitally.

Wally

@CaLviNx - which connector are you using for "external 5v in socket" ?
I'm having trouble locating this connection in the diagram here, https://duet3d.dozuki.com/Wiki/Duet_3_Mainboard_6HC_Wiring_Diagram#main

oozeBot

@Wally it's circled in red.. but you'll need to modify the jumpers right below it.

Wally

@oozeBot - Thank you for the help. I'm using that currently to control a solid state relay to power on/off 120VAC input to my main power supply. So explains my confusion...

oozeBot

@Wally note that this is what I asked above for clarification on if this is still a recommended setup..

Wally

Ahh, thank you - yes this is a good question..

So, the big question is where else can we connect 5 VDC input to the Duet 3 if "EXT 5V" is consumed for PSON (power supply on)? In my case, applying 5 VDC here would power the solid state relay and defeat the PSON feature.

Currently, I power the Duet 3 via the micro USB connector (5 VDC) - is this they only work around? I'm not keen on soldering stuff to the expensive Duet 3 board.

oozeBot

I literally have one set up this way right now on my desk.. it appears to be the ideal setup for us. I just want @dc42 blessing after reading a few of his comments..

edit: and my photo is upside down.. lol

Wally

@oozeBot - thanks for the picture - literally worth a 1000 words....
PS: I have a very similar setup too!

T3P3Tony

This is the current documentation on the 5V options for the 6HC:

https://duet3d.dozuki.com/Wiki/Duet_3_Mainboard_6HC_Hardware_Overview#Section_5V

Please let me know if it needs further expanding.

To answer the specific question of providing external 5V to the Duet and also to the RPI

While this is possible in theory:

EXT 5V -> Duet, and then Duet -> Pi over the ribbon cable

~~you then have multiple diode drops in the protection circuits~~
Edited as there is only 1 diode drop
its not recommended.

If you want to use an external 5V (suitably rated) to power both Pi and the Duet then you connect them in parallel:
EXT 5V -> Duet (on the EXT 5V header)
EXT 5V -> Pi

The safest way to power the Pi is through the USB C socket, the 5V pin on the SBC header bypasses some of the internal protection.

oozeBot

@T3P3Tony thank you for this clarification.. it was a concern we had that we had not been able to find a clear answer on.

A Former User

@T3P3Tony said in How big a 5v power supply needed for Duet 3 and RPI4?:

This is the current documentation on the 5V options for the 6HC:

https://duet3d.dozuki.com/Wiki/Duet_3_Mainboard_6HC_Hardware_Overview#Section_5V

Please let me know if it needs further expanding.

To answer the specific question of providing external 5V to the Duet and also to the RPI

While this is possible in theory:

EXT 5V -> Duet, and then Duet -> Pi over the ribbon cable

you then have multiple diode drops in the protection circuits so its not recommended. (and probably wont work)

If you want to use an external 5V (suitably rated) to power both Pi and the Duet then you connect them in parallel:
EXT 5V -> Duet (on the EXT 5V header)
EXT 5V -> Pi

The safest way to power the Pi is through the USB C socket, the 5V pin on the SBC header bypasses some of the internal protection.

@T3P3Tony

This being so are the 5v lines on the SBC header pins considered dead when you only have the jumper "Int 5V EN" shorted ?

Edit i have just remembered ( I will try to find the thread) that there was a thread about this very thing when the first batch of Duet-3 boards were pre-released .

EXT 5V -> Duet, and then Duet -> Pi over the ribbon cable

you then have multiple diode drops in the protection circuits so its not recommended. (and probably wont work)

It does work i have one wired that way (and wired it that way after the it was being discussed previously)

oozeBot

I just measured a .33v drop at the RPi based on the way its wired in the photo I posted above. By adjusting the 5v power supply, I was able to deliver 5v to the Pi. I do understand this is bypassing the RPi's power regulator though.. so I'm torn. If this was just for myself, I think I'd trust it, but if Duet can't recommend this setup, I am afraid we'll have to rethink it..

A Former User

@oozeBot said in How big a 5v power supply needed for Duet 3 and RPI4?:

I do understand this is bypassing the RPi's power regulator though..

Pi doesn't regulate 5v, within lies the problem

T3P3Tony

I have edited my reply as i was working from memory and thought there was another protection diode where there is not (thanks oozebot for checking the voltage drop).

There is only one diode drop and its thus possible to have 5.x volts on the 5V exp header and then have 5V on the pi header (x depends on the exact diode drop).

T3P3Tony

And regarding using the GPOI header to power the 5V on the Pi (like the Duet does). Connecting an unregulated 5V supply to those pins is not recommended (see a long discussion about it here)

https://raspberrypi.stackexchange.com/questions/1617/how-do-i-supply-power-through-the-gpio

In the case of the Duet powering the pi the internal 5V regulator is regulated with over current protection, however as has already been printed out a RPI4 with HDMI screen and other peripherals will be too high current for the internal regulator which it why powering the Pi from its own official supply is the safest option.

oozeBot

OK, great! This makes me feel much better about the direction we took as we are not recommending any peripherals other than a webcam.

And to the OP - if interested, the 5v power supply we are using in the photo I posted is a Meanwell LRS-50-5

https://www.meanwell.com/productPdf.aspx?i=399

Thanks

Nuramori

I use a meanwell RD-65a to supply 5/12v, combined with a meanwell 150w 24v psu (I have a ac heated bed). The Ed-65a works extremely well and is fanless so it’s quiet.