User avatar
Imperf3kt
Posts: 355
Joined: Tue Jun 20, 2017 12:16 am
Location: Australia

Re: Painfully slow performance

Thu Dec 07, 2017 8:11 pm

jamesh wrote:
Thu Dec 07, 2017 8:05 pm
Imperf3kt wrote:
Thu Dec 07, 2017 7:50 pm
The more I come across the undervoltage issue, the more I suspect it should be called undercurrent.
The circuitry on the board detects the VOLTAGE dropping below 4.63+=5%, at which point the icon will be displayed.
Yeah but is that caused by the cable being unable to handle the voltage or the cable being unable to handle the current, resulting in voltage sag.
Pi3b - 'normal use' temperature (25% CPU load) 76℃, ambient 21℃

User avatar
davidcoton
Posts: 2430
Joined: Mon Sep 01, 2014 2:37 pm
Location: Cambridge, UK

Re: Painfully slow performance

Thu Dec 07, 2017 9:08 pm

Imperf3kt wrote:
Thu Dec 07, 2017 8:11 pm
Yeah but is that caused by the cable being unable to handle the voltage or the cable being unable to handle the current, resulting in voltage sag.
The problem detected by the Pi is undervoltage, not undercurrent.
Undervoltage can have two (common) causes:
  • The PSU itself cannot generate enough voltage, sometimes it will be OK when not loaded (Pi shut down) but low voltage at the running load (current).
    This is common with supplies designed as chargers. They may be marked 5V 2A but cannot supply 5V and 2A at the same time.
  • The PSU generates enough voltage, but there is a voltage loss in the cable between PSU and Pi at the running current, due to thin and/or long conductors and Ohm's Law.
Both may be related to current draw but the problem in each case is the low voltage at the Pi. The solution may be to improve the current capacity of the PSU and/or cable.
If you must call it "undercurrent", it is "inadequate current capacity". From the PSU/cable POV, it is actually an overcurrent condition -- the Pi is drawing more than the PSU/cable can supply without excessive voltage loss.

An analogy:
Your water supply pressure is low. You need either a taller water tower, or a thicker and/or shorter pipe, or just use less water.
"If it ain't broke, fix it until it is."
“Raspberry Pi is a trademark of the Raspberry Pi Foundation”
The Pink Unicorn is a symbol of commitment to sensible discussion of future versions of the Raspberry Pi ™

abyssdj
Posts: 14
Joined: Wed Dec 06, 2017 9:32 pm

Re: Painfully slow performance

Thu Dec 07, 2017 11:19 pm

The voltage measured over the GPIO pins is >5. I am going to try a bigger power supply though. I can get a 12v - 5v/3a dc to dc transformer which I was going to use as an in car supply anyway so maybe that will help.

The problem is not heat, the sensor reads <50. The board does smell bad though, I may get it replaced based on that. Maybe a bad solder joint is causing the power issues.

User avatar
Imperf3kt
Posts: 355
Joined: Tue Jun 20, 2017 12:16 am
Location: Australia

Re: Painfully slow performance

Fri Dec 08, 2017 12:34 am

Are you measuring the voltage with a digital multimeter, or an analogue voltmeter?
A multimeter is not accurate/fast enough.
Pi3b - 'normal use' temperature (25% CPU load) 76℃, ambient 21℃

Return to “Troubleshooting”

Who is online

Users browsing this forum: asandford, portafreak and 42 guests