Can I use a Raspberyy Pi 4 PSU for a Pi 3+??

[Chris Wilson]

I am getting a new Raspberry Pi 3+ without a PSU. Can I buy a Pi 4 official PSU to use with it, or in future with a pi4? Thanks.

[sokoloff]

Raspberry Pi 3 power comes in over USB micro.
Raspberry Pi 4 power comes in over USB-C.

RPi3 should work with most regular USB power sources. You probably already have one lying around.

[Chris Wilson]

Ahh! I see, thanks for that, I probably have!

[SiliconWizard]

Yeah, if you are ready to butcher the RPi4 PSU to adapt its connector for the RPi3, have at it. The Pi4 is more power hungry than the 3, and its official PSU can definitely deliver more power, whereas many PSUs that were meant for earlier RPIs versions were a bit underpowered. I even think the official Pi4 PSU is the first official one that was sized correctly. They even went as far as setting the nominal output voltage to 5.1V instead of 5V, to make sure that the Pi would get high enough voltage even at full load.

"RPi3 should work with most regular USB power sources" => I would change that to "some". Make sure it can deliver at least 2.5A peak. Many also have horrible cables that yield significant attenuation at high currents, thus you end up with an supply voltage below what's recommended for the PIs. All the more that Pi3 and earlier were picky about that.

[Ian.M]

It very much depends on what you have hung off the PI's USB ports.   I have a Pi 3B running off a 2.1A micro USB PSU, with a 2.5" SATA drive (spinning rust, not SSD) in a USB enclosure, and I've only ever seen the low voltage warning if I've connected another power hungry USB device.

[Chris Wilson]

Thanks for the further detail, appreciated. If I could find a decent lead terminated in a micro USB plug I would build a small linear supply for various 5V "things". I suppose I could chop up a micro to USB A lead... Most seem very thin for the current they could potentially be asked to carry.

[Ampera]

If you want to build your own supply for fun that's one thing, but the pure abundance of generally not shit 5V supplies is like trees in a forest. Finding a USB power supply capable of 2.5A constant and a USB Micro-B cable should be dead simple. I have tons of them laying around.

[rstofer]

Do some research, some folks are using 5.1V
Amazon has some PSUs with an in-line switch.  This is really handy.

[SiliconWizard]

Do some research, some folks are using 5.1V
Amazon has some PSUs with an in-line switch.  This is really handy.

I second the "handyness" of a switch (make sure the PSU itself is of reasonable quality). When you have to power-cycle you Pi a lot (for instance when you're trying stuff), plugging and unplugging the cable is a royal pain, and will eventually destroy the connector.

[rstofer]

Do some research, some folks are using 5.1V
Amazon has some PSUs with an in-line switch.  This is really handy.

I second the "handyness" of a switch (make sure the PSU itself is of reasonable quality). When you have to power-cycle you Pi a lot (for instance when you're trying stuff), plugging and unplugging the cable is a royal pain, and will eventually destroy the connector.

Or, as is the case with the PiDP11, the Pi is inside a closed box and there is just a USB micro jumper to a micro USB jack on the back panel.  Plugging and unplugging the cable to the jack is a real PITA

It is also problematic when power is interrupted to a Pi.  You WILL scramble the file system if you don't issue a 'sudo shutdown -h now' command and wait for the green LED to quit flickering.  Or just wait about 30 seconds (way overkill) before turning the power off.  Of course, if the Pi is inside a closed box, you can't really watch the LED.  Hence the long delay - you're just guessing the system has finished writing...  Did I mention how little I like the Pi filesystem?  It's not unique to the Pi but that isn't very satisfying when you are building the system image for the <insert a number here> time.

https://obsolescence.wixsite.com/obsolescence/pidp-11  <== a really fun project.  Mine are running 2.11BSD Unix, a very complete distribution.

[station240]

Just get a USB-C to USB micro adapter/cable, if you still want to use the Pi4 PSU.

[HarryMan]

Since the connections are different, it is better to buy each Raspberry its own power supply. Moreover, they are not expensive