Raspberry Pi 3B+ low voltage

[N6NG]

I’ve tried 4 different power modules for the Pi 3B+ and no matter which I use, I get the Low voltage warning --Please check you power supply messages. I tied to use a Pi4 supply but which is 3 instead of the 2.5 but that doesn’t fit.
Anyone else see this behavior?
Thanks all mostly Sam
Dennis N6NG

[sdetweil]

@N6NG I ordered a 6 amp ps for my p4
and a 5 amp for my pi3

[N6NG]

@sdetweil Where?

[MillerM]

The power supply you are using must provide 5V and 2.5A to satisfy the voltage and amperage requirement of the Raspberry Pi 3B+.

[sdetweil]

@N6NG Amazon…

[Fozi]

@N6NG The key is to have a power supply which provides constantly and reliably the specified VOLTAGE. Thus, the warning states “Low Voltage”. The amperage, which the power supply can provide is of secondary interest.
The PSU can deliver a much higher amperage than the 2.5A, but that doesn’t mean that the RPi will also draw them. This is the maximum amperage that the PSU could deliver. The RPi draws only as much current (amperage) as currently need (depending on attached USB devices, read/write cycles to SD card, processor loads, Wifi usage, etc.), while voltage remains constant. So, the power and amperage drawn from the PSU varies lineraly over time (at constant voltage).

For example:
Power = voltage x amperage, also known as P=U x I
The maximum deliverable power for the RPi is: 5V x 2.5A = 12.5W.
But as said before, the RPi doesn’t consume that much power. Usually it hovers something around 1W - 3W, depending on usage (or calculated in amperage 0.2A - 0.6A).

That said, amperage is sufficiently provided by the PSU, what you want is constant voltage at minimum 5V. Higher amperage will not solve the problem. You could also try to find a PSU which provides 5.1V or 5.2V for the RPi. That small increase in voltage can be handled easily by the RPi. A search on Amazon might be successful.

EDIT: And stay away from mobile phone chargers connected to the RPi with a USB cable. That will hardly work reliably.

[sdetweil]

@Fozi i went with more amps = more watts, cause I am constantly changing/adding the attached devices… (and the cost difference is noise)

[Fozi]

@sdetweil LOL…right, I do the same:beaming_face_with_smiling_eyes:
I tried to explain to @N6NG that the amperage the PSU delivers is not decisive for his problem, esp. for the RPi, which practically never reaches the max power spec of a PSU. It is the linearity and constancy of the voltage.
I see too many post e.g. on reddit, where people have similar problems with their 3D printers and attached RPis and unfortunatelly every time the get the advice to get a PSU with higher amps.

@N6NG : Oh, by the way…If you are using a USB extension cable, then remove it and plug the PSU directly into the RPi. Depending on the quality of the extension cable (which is commonly low), there might be a voltage drop of due to the resistance of the cable, which results in lower input voltage on the RPi.

[N6NG]

@Fozi I’m using the psu that came with the RPi 3B+. I have no extension cables. The only things I have attached is the HDMI monitor, Bluetooth keyboard and the SD chip. I wouldn’t think that would be too much for standard psu I’ll take a look at Amazon and get something with a little more umph. Thanks all for the lessons. Dennis