Currently using the ATXRaspi r3 with a Mean Well RS-25-5 power supply, rated 5v 5a.
The RPI is running MainsailOS with Klipper for my 3d printer setup and is not overclocked.
Problem; Under Voltage (UV) warning on the RPi 4b.
I have resoldered the power pins on the ATXRaspi making sure the pins have a good connection.
Main power supply cable size is AWG24 from PSU to ATXRaspi approx 150mm in length (6")
Powering the RPi from ATXRaspi to the RPI GPIO 5v and Gnd pins with AWG24 cables and approx 120mm in length (5").
Devices connected the RPI:
A single Wyze webcam connected via USB.
Devices connected to the ATXRaspi:
A single Winsinn 4010 5v 0.17a 0.85w fan to the 5v output pins.
Solutions I found are:
1. Removing the ATXRaspi from the circuit eliminates the UV warning.
2. Removing the 5v fan from the ATXRaspi eliminates the UV warning.
Why would the draw of 0.17a connected to the 5v output pins on the ATXRaspi cause the under voltage?
There is always some voltage drop through the ATXRaspi. It was designed with components that should keep that to a very minimal value (ie minimal ON resistance resulting in minimal voltage drop).
Usually the biggest culprit in voltage drops (resulting sometimes in voltage warnings if the drop is more significant) are the power connections.
Poor connections, thin / low quality wires, corroded/oxidized or just poor contacts between the PSU->ATXRaspi and ATXRaspi-Pi will act as more resistance added on the way to the Pi (and consequently more drop).
AWG24 sounds like a pretty thin wire IMO. That's where removing the fan's small load can actually make the difference between a warning and no warning, it goes back to how much voltage drops across that thin wire. Depending on the composition (stranded, solid, copper or copper plated aluminum) these wires could easily cause an issue.
I would go with beefier wires on the Power lines.
And in terms of solid connections, soldering is the top choice. High quality dupont jumpers are good and I offer some in my store. USB connectors are also OK, but I have seen some crappy cables and/or crappy USB connectors on these chinese cables so stay away from such cables.
Hi Felix,
Thanks for your reply and advice.
I have since increased the main power supply cables from AWG24 to AWG18 leading to and from the ATXRaspi r3.
I attached the 4010 fan back to the 5v output on the ATXRaspi to test again however this resulted in the warning once again.
The only thing I have not done is soldered the cables directly only because I like the convenience of disconnecting quickly, however.... because I'm only getting the warning when a fan is connected to the ATXRaspi I have now powered a smaller 5v 3010 fan from RPi GPIO pins, with no warning appearing.
I'll leave it connected this way for now as all seems quite stable with the fan powered this way.
Thanks again for your help.
Ah, that's quite a revelation. It could be that the fan is causing ripple which is being picked up as undervoltage depending how the voltage monitor is sampling the supply.
That could be confirmed if you hook up a scope to the 5V rail on the Pi in question.
:( unfortunately I do not own a scope, but thank you.
Could be the cheap 4010 fan I used, however I never swapped the fan to check if that was the culprit.
I will keep investigating.