External 5v Source

A Former User

At the moment you have a PSU that switches on when a pin is pulled low,

he said the opposite in his last post? which i assumed is what all the fuss with the meanwell psu's a while back was all about as well

GoremanX

@achrn With M80/M81 reversed, I can connect the + (plus) from the remote control to the EXT_5V pin, and the - (minus) to the ps_on, and then switch the power supply off by switching its - (minus) between pulled low and floating, no pullup resistor needed. In fact, this already works when I wire it up that way. M80 turns off the power supply and M81 turns it on (which is backwards)

achrn

@GoremanX Thanks, I understand now.

GoremanX

@dc42
Out of curiosity, how much current can the ps_on pin sink? Am I stressing that circuit by running 23 mA through it almost constantly? I'm trying to find a spec for it, but I'm failing

A Former User

23mA? Thats nothing (0.023A). Don't recall of the top of my head which type of connector it is, but iirc 6 amps if its the big type used for motors on the Duet3 and 2-3 amps if its the smaller type used on the Duet2. So in any case you're at or below 0.1% of its rating with 23mA.

Edit: its the mosfet; right. Ehm, max raing is around 4A. But should probably stay below 2A without cooling.

GoremanX

@bearer I vaguely remember reading something about 200ma, but that may have been for drawing power from the 5v_ext pin (which is essentially what I'm doing, and shunting it to the ps_on pin)

A Former User

That is indeed a different question than how much current the ps_on pin can sink.

On the Duet3 I guess if you don't supply external 5v you'll be pulling internal 5v through a 0.25w 220R resistor.

As long as you don't exceed 5v you can't exceed 50% of that 0.25w rating so not an issue, but sounds like you'll be loosing a lot of your 5v across that resistor.

On a Duet 2 you can't source any current from that pin, ints purely an input afaik.

Nuramori

@javitopia said in External 5v Source:

Just think of the mosfet (the device controlling the pin) as a switch between the pin and GND.

...

and lastly @oliof YES if you feed 5v via the ext 5v header you have to remove the int_5v jumper.

Is there a danger by not removing the int_5v jumper if you supply 5v to the external header on the duet3? I think I had it that way (jumper removed), then one day things stopped working until I jumpered it again. The supplemental PSU (meanwell rp65A) does 12v and 5v and works fine.

dc42

I am late to the party, but unless you are powering LED strips or other high current 5V devices from the Duet, then I suggest you power the Duet 5V from the Pi 4 using the 5V SBC->Duet jumper, and use the official Pi PSU or similar to power the Pi. The Duet only draws around 200mA from 5V.

GoremanX

@dc42 That's what I ended up doing and it works really well

dc42

@GoremanX said in External 5v Source:

@dc42
Out of curiosity, how much current can the ps_on pin sink? Am I stressing that circuit by running 23 mA through it almost constantly? I'm trying to find a spec for it, but I'm failing

PS_ON can sink about 1.5A, same as the fan outputs; but it doesn't have a flyback diode built-in.

GoremanX

@dc42 Perfect, thank you