Raspberry Pi under voltage warning
 

Hi there,


I don't know if this is the right place to post it, but I did not get answer from the official forum.


I am using a Pi 4B with 8G, I got under voltage warning when booting with USB. I am using a phone charger capable of producing 3A@5V same as the stock adapter that I don't have. The Pi works normal when booting with MicroSD, but on and off I got under voltage warning when booting with different made of USB HDD, flash and SSD, before I order the original adapter I want to make sure my Pi has no h/w problem. Since I don't have the tool to check the current drawn at the moment I can't tell if I really need a high capacity adapter, but I overclocked the Pi to 2.2Ghz, that will definitely drain more current, so I will try slowing it down to see what comes, but I still want to know if anyone has any problem like mine ?

yes, buy a better PSU. Usually phones do not require 3A (but only 2Amps). And also you can buy a 3.5A PSU if you really want to be on the safe side.

It depends on the type of phone charger. Some Iphone chargers are smart devices and don't output full current unless the phone "asks" for it. If so you will need a regular PSU.

Moderator Response
 

Moved: This thread is more suitable in <Linux - Embedded & Single-board computer> and has been moved accordingly to help your thread/question get the exposure it deserves.

I agree with the previous posts. I started out with a Pi 3B which is quite power hungry. I noticed that running pi on the windowsill during winter eliminated the undervolting and was way more snappy than in the summer. Later I also spliced two usb cables together and used two charging bricks for a while because I couldn't afford to get the 3amp one designed for the pi, not sure I'd recommend this but it does work if you are broke;) I finally found a charging brick that could actually supply the power I needed. No idea what it's off of but it packs punch.

More recently some friends of mine got the pi 4 and the OEM power brick, no problem with undervolting with that.

The problem with phone chargers is that they don't supply constant voltage/ampage, but a proper PSU does, it really is false economy trying to use a charger, & you could possibly lose data.

I've heard so many stories of people having problems with anything other than a 3.5A/5V PSU, especially as you load up your RPi with devices. Bite the bullet and get the proper one, when you can, if you want to save yourself aggravation that comes from underpowering your Pi.

TKS

With standard recommended power supply, I was fine with booting off an external SSD. Right now my RPI4-8G is running off a Samsung 500GB T7 in fact. However awhile back I plugged in a 4TB external HDD in the other USB 3.0 port and started having voltage problems. I solved it by buying another 4TB HDD that was self powered (power cord for external drive, and power cord to the RPI). Not the solution I was looking for, but it worked.... Probably could buy a powered USB3.0 hub to accomplish the same thing, but still two power cords to plug into the wall.

There are two considerations here. First, as others have pointed out, using the phone charger is probably not a good idea. If you can afford it, get one of these 3.5amp models:

https://www.amazon.com/CanaKit-Raspb...3247880&sr=8-3

https://www.amazon.com/CanaKit-Raspb...3248175&sr=8-7

Second, you should be aware that the two usb3 ports on the Pi 4 have a combined load limit of 1.2 amps which is lower than the usb3 standard spec for two usb3 ports of 1.8 amps(0.9 amps per port). What this means in practice is that your Pi 4 will begin to act erratically anytime you start drawing more than 1.2 amps from the usb3 ports. This can occur if you have more than one usb storage device connected to your RPI4. I've also had it occur under heavy I/O on some single usb storage devices and I have one of the above 3.5 amp psus. Worst offenders - an nvme pci drive in a usb adapter and standard 2.5 in hard drives in a usb adapter. These items just draw too much power, especially the nvme drive. Standard SSDs in an unpowered usb adapter are OK as long as you only plug in one at a time. Ultimately, I wound up getting a powered usb hub to resolve the issues that would pop up when using usb storage.

Under voltage warning
 

Many times the under voltage results from voltage loss in cable from source to board. The charging cables usually have very THIN wires 26 or 28 gauge. This can lead to substantial voltage drop by the time it gets to the board. I hardwired a little voltmeter to power on GPIO pins to see if the voltage drops across the board. Short USB cable used less power loss.

Thank guys for the response, the problem seems to have fixed when I use the original power adapter, I no longer get the under voltage warning. There is one more thing may not related to the power adapter, I found not all SATA SSD drives boot normally via USB adapter, it seems some adapter does not provide enough current to the drive, and some drive draws more current than others, WD green vs Verbatim for example. As far as I see SSD normally takes 0.7 Amp at 5V which is same as 2.5" mechanical drive, but Samsung EVO takes more than that so won't boot from the front USB port on Lenovo desktop, and I believe booting NVMe which known to be power hungry, via the Pi USB may be more of a problem too.

You might be interested in the work by the James Chambers : https://jamesachambers.com/best-ssd-...erry-pi-4-400/

I personally found that Samsung T5s and T7s (500GBs) work the best for me for booting RPI-4 from USB 3.0 . I've also had good luck with older 2.5s (128GB/256GB) with a sata to usb adapter as well.

Being a hardware techie, I feel your pain. I solved it with a 5.1V power supply.

That said, which supply is undervolting? There is a low voltage supply for the cpu cores, and it is adjustable on the later Pi 4Bs. That doesn't include my earlier model, unfortunately.I very much suspect the cpu core is what's undervolting. Look it up, but I think you can increment this cpu core voltage with a line in /boot/config.txt

overvolts=<number>

Articles about overclocking the Pi will give you the syntax :D.

EDIT: There are problems with the original "official" PSU. I think it's transformer based for 240VAC whereas the rest of the world uses 220VAC. That varies wildly anyhow. So the average install has very little overhead and comes out at 5.0V. By the time you've got down the wires and into the board, of course, you have lost some of that 5.0V. I got a switchmode power supply @ 5.1V.

Thank guys for the valuable input, my problem basically solved. in the pass I used phone charger and even backup battery that I already have to save some cost, while running at normal clock rate booting via microSD I've no problem at all, the under voltage problem started to show after I overclocked and boot via USB.
@business_kid : I got 220V AC here, and I suppose modern PSU are switchmode should be able to adjust for that, I will take a measurement with those USB meter thing to see what actually the Pi receiving, thanks for the tip !

You're welcome. I believe the fussy voltage is actually the CPU voltage, and you can use an overvolts= option to increase that. I have this in my RazPi I'm overclocking to 2.0Ghz, although it does go a bit higher. You could gradually start at 1 and just increment it to see if that loses the undervolts thing.