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

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.