Duet 3 powering via ext 5v

frontofit

@nurgelrot I will be sure to post as soon as I find out! You are correct about the starvation on the Pi side when it comes to a Pi 4 as the power requirements (for the Pi) are somewhere in the ballpark of 5A whereas the Duet is only able to supply 3A max on top of any other peripherals that require a 5v source. The symptoms usually show up as a warning on the Pi.

I have also read about solutions where the SBC can power the mainboard but something about it just feels wrong, also since that LRS-100-5 can supply up to 18A, I figure why not use it to also supply the duet.

I figured with all of the people on this thread it should have been a slam dunk to get an answer by now. I will post my findings if I decide to give it a go on my own. Hopefully I don't cook any boards haha

gtj0

@frontofit Yeah it's a little confusing and I believe the schematic isn't actually correct with respect to the power control jumpers. Anyway, the +5V pin on the EXT_5V connector is really meant for control only. It has a 220ohm resistor in series and is meant to supply voltage to an external SSR. This way, when the PS_ON pin goes low, the SSR is energized and turns something (presumably an external 12/24V PSU) on. You can't really provide power to the board via this connector.

There is no dedicated pin for providing external 5V power but you still have a few options...

If you don't plan on using the PS_ON pin to control an external 12/24V PSU and you're going to have your 12/24V PSU on all the time, then you can use the internal 5V regulator to power the logic.

If you are, then you can do what I do... Remove the MIDDLE jumper from the power control header and connect your 5V supply to the middle left pin on that header. That's the same pin that would be supplying power to the Duet from the SBC if the jumpers were in place. Note though that there's no protection on those pins so your supply has to be fairly stable. Since it's the same one powering the Pi, then that should be no problem.

One other thing I do that you might find handy is run the Duet's 5V supply through a relay or switch so you can quickly power off the Duet if you have to.

gtj0

@gtj0

oops, had an error in the original pic.

You need to jumper the two bottom pins and provide power to the middle left pin.

Nurgelrot

Sigh. All I want to do is trun on and off the 24v supply with M80/81 while the pi keeps running... So friggin confusing...

gtj0

@nurgelrot said in Duet 3 powering via ext 5v:

Sigh. All I want to do is trun on and off the 24v supply with M80/81 while the pi keeps running... So friggin confusing...

What's still confusing? Jumper the two bottom pins and provide power to the middle left pin.

Alex.cr

@Nurgelrot
The following write up applies to the Duet 3 as well.

https://duet3d.dozuki.com/Wiki/Power_Wiring

Apply 5v and ground to the respective pins of the 5v header, run 5 v power from your supply to the control pin on the SSR and ground to the ps-on pin. Everything will work, this is what I am doing. I removed all jumpers for 5v power.

Edit: M80/81 will drive the SSR like you are looking for.

Also one downside I have noticed is if you are using expansion boards they will not have power on start up and this will cause all kinds of errors upon start up. You can put M80 in your start code but I am also using this to cut power if my mains heated bed has an SSR runaway. Still have to find a work around for that.

gtj0

@alex-cr said in Duet 3 powering via ext 5v:

@Nurgelrot

https://duet3d.dozuki.com/Wiki/Power_Wiring

Careful, that link actually doesn't apply to the Duet3.

Nurgelrot

@alex-cr Thank you that finally makes sense. It's working as expected. So no power going to or from the SBC. EXT_5v powering the board (or at least enough of the board to open the relay for VIN).
@gtj0 I don't need the whole duet powered since the SBC is handling DWC just need that PS_ON to work when called from the SBC which is powered from 5v all the time. I'm working on a plugin DWC to just do it all with a network connected mains relay. Tired of messing around with all the configs on the boards. One of the great things about Duet is how configurable they are... but at times that can also be a pita
Thanks every one.

gtj0

@nurgelrot I think I understand... If you have an SSR or other low current control mechanism of the 12/24V PSU, then you can set the Duet to use the internal 5V regulator and switch the psu control directly from an SBC GPIO. The SBC can then turn on the PSU which will automatically power on the Duet.

Alex.cr

@gtj0

Careful, that link actually doesn't apply to the Duet3.

It works for my Duet3 6HC without major issues. The only piece of information missing is to pull the SBC jumpers.

gtj0

@alex-cr said in Duet 3 powering via ext 5v:

@gtj0

Careful, that link actually doesn't apply to the Duet3.

It works for my Duet3 6HC without major issues. The only piece of information missing is to pull the SBC jumpers.

Yeah you're right. Every time I look at the schematic, I get a headache.
The description for the PS_ON header says...

3-pin KK labelled PS_ON: open drain mosfet output for controlling an ATX-style power supply or a SSR. The +5V pin can also be used to provide external 5V power. A small amount of 5V power can be drawn from this pin (through an internal 220 ohm resistor), so that the control terminals of an SSR can be connected directly between the +5V and PS_ON pins. Note: on the v0.5 board this connector is rotated 180 degrees compared to the intended orientation on later version boards.

It doesn't actually say that you can PROVIDE power via that header.

The schematic does show that you can input 5V from that header but if you try to draw 5V from it, it goes through the 220ohm resistor.

The power options do seem to be spread out.
https://duet3d.dozuki.com/Wiki/Duet_3_Mainboard_6HC_Hardware_Overview#Section_Power_distribution doesn't even discuss the PS_ON header.