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Re: RPi 3B+ 5 volt lines

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In message <NLy*uFPHz@news.chiark.greenend.org.uk>
          Theo <theom+news@chiark.greenend.org.uk> wrote:

> David Higton <dave@davehigton.me.uk> wrote:
> > The upshot is that I'm going to have to reconsider power supply and
> > distribution for this one, which is used as NAS, so it needs to power
> > some spinning drives.  The incoming supply is rated at 8 amps, but its
> > output voltage is just 5V, and it appears that its transient response may
> > leave something to be desired.  One thing I can try is whacking several
> > 1000uF capacitors, via short leads, on the 5V line on the GPIO
> > connector. I can also see where I would need to interfere with it so
> > as to increase the output voltage to about 5.1V.  I've cut the output
> > cabling as short as it can reasonably be made so that cable resistance
> > genuinely can be neglected.
> 
> FWIW I've just installed a 3B in my 3D printer to run Klipper.  It's
> powered off the main 24V PSU via a Chinese '5V 5A' DC-DC module, which
> outputs 5.2V under no load.  Klipper was running fine but reporting a
> number of power supply dropouts, despite no USB devices connected.
> 
> I fitted a 330uF electrolytic and a 22uF ceramic (for low ESR) across the
> power rails at the power input to the Pi (here via GPIO) and that resolved
> the dropout problem.  I'd guess the DC-DC just has insufficient capacitance
> to hold up the rail when the Pi takes a gulp of current, and so needs a bit
> of help.
> 
> I don't know the frequency response of the Pi's PDN (whether the gulps of
> current are seconds, milliseconds or microseconds) but maybe try a range of
> capacitors to handle them - not just big electolytics, which can have high
> ESR and so a slow frequency response.

I've just tried 9000uF (9 1000 uF capacitors in parallel) this afternoon.
I didn't see a restart in the logs when Clonezilla did a backup to OMV,
but the backup failed anyway, and now I don't know why.

I'll have to get the DSO on the job.

I've also got a bench PSU with enough current for this job, and of
course that enables me to set the voltage where I want.

David

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RPi 3B+ 5 volt lines David Higton <dave@davehigton.me.uk> - 2024-04-11 21:59 +0100
  Re: RPi 3B+ 5 volt lines Theo <theom+news@chiark.greenend.org.uk> - 2024-04-12 10:12 +0100
    Re: RPi 3B+ 5 volt lines David Higton <dave@davehigton.me.uk> - 2024-04-12 21:21 +0100
      Re: RPi 3B+ 5 volt lines Theo <theom+news@chiark.greenend.org.uk> - 2024-04-13 11:32 +0100
        Re: RPi 3B+ 5 volt lines David Higton <dave@davehigton.me.uk> - 2024-04-13 18:42 +0100
          Re: RPi 3B+ 5 volt lines David Higton <dave@davehigton.me.uk> - 2024-04-14 22:35 +0100

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