benoit_f
Posts: 4
Joined: Sat Nov 02, 2019 5:13 pm

Under-voltage when using USB storage

Sat Nov 02, 2019 5:45 pm

I use a RPi3B+ for remote backup.
It's powered with a 5.1V / 2A Asus power supply.
2 USB hard disks, with their own power supplies, are connected to the RPi.

At my home, it was OK.
When I installed the RPi at my mom's house, it rebooted after some hours, even without any load.
I replaced the default USB cable with a Rampow Nylon Braided cable. No more reboot.

Unfortunately, as soon as there is I/O, reboots occur again.
I tested very high CPU load, and it's OK.

For now, the only solution I found is to limit I/O to 100 kBps. Far from satisfactory!

I previously used a SheevaPlug, with the same USB hard disks, without any issue.

Do you have any idea?

Thanks

pfletch101
Posts: 634
Joined: Sat Feb 24, 2018 4:09 am
Location: Buffalo, NY, USA

Re: Under-voltage when using USB storage

Sat Nov 02, 2019 9:45 pm

You are using a 'power supply' (probably really a charger) which is under-specified for your Pi, even if one assumes that the specifications are valid in this context. Why are you surprised that you are having power problems? Buy and use an official Pi power supply.

benoit_f
Posts: 4
Joined: Sat Nov 02, 2019 5:13 pm

Re: Under-voltage when using USB storage

Sat Nov 02, 2019 10:18 pm

From the start, I assumed that RPi were to be used with any phone charger. And it was OK with my RPi 1B & 2B... That was great, cause it was cheap to reuse all that old phone chargers. ;) Of course, I made sure to use some branded stuff.

Can you please explain (or give me a link explaining) the differences between a charger and a power supply? Except from the official store, how to identify a power supply from a charger?

Thanks

epoch1970
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Joined: Thu May 05, 2016 9:33 am
Location: Paris, France

Re: Under-voltage when using USB storage

Sat Nov 02, 2019 10:48 pm

Chargers don’t mind varying voltage as well as intensity.
A PSU tries to delivers constant voltage, up to its limit.
The official PSU provides adequate power, is well built, and quite inexpensive.
"S'il n'y a pas de solution, c'est qu'il n'y a pas de problème." Les Shadoks, J. Rouxel

benoit_f
Posts: 4
Joined: Sat Nov 02, 2019 5:13 pm

Re: Under-voltage when using USB storage

Sat Nov 02, 2019 10:59 pm

I will order one, hoping this will solve my problem.
Thanks.

(But I still not understand why voltage shortage occur when there is high I/O, and not when there is high CPU load)

pfletch101
Posts: 634
Joined: Sat Feb 24, 2018 4:09 am
Location: Buffalo, NY, USA

Re: Under-voltage when using USB storage

Sun Nov 03, 2019 12:24 am

benoit_f wrote:
Sat Nov 02, 2019 10:59 pm
I will order one, hoping this will solve my problem.
Thanks.

(But I still not understand why voltage shortage occur when there is high I/O, and not when there is high CPU load)
I had missed your original statement that the USB drives had their own power supplies. However, even with external (typically 12V) power to run the hardware, they may well be drawing 5V power from the USB ports of the Pi to supply the logic chips. Since a standard USB port may be expected to supply 0.5A at 5V, a powered USB drive can reasonably expect only to have to 'top that up' to whatever it needs.

benoit_f
Posts: 4
Joined: Sat Nov 02, 2019 5:13 pm

Re: Under-voltage when using USB storage

Wed Jan 01, 2020 5:24 pm

I finally replaced my USB charger by the official PSU, and I do confirm it solved my issue. Thanks.

I am just a little disappointed RPi cannot be used any more with any USB charger as it was possible with RPi 1 or 2.

jamesh
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Re: Under-voltage when using USB storage

Wed Jan 01, 2020 7:23 pm

benoit_f wrote:
Wed Jan 01, 2020 5:24 pm
I finally replaced my USB charger by the official PSU, and I do confirm it solved my issue. Thanks.

I am just a little disappointed RPi cannot be used any more with any USB charger as it was possible with RPi 1 or 2.
Extra performance and features means extra power required - that's just the way it works.
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HawaiianPi
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Re: Under-voltage when using USB storage

Wed Jan 01, 2020 9:00 pm

benoit_f wrote:
Wed Jan 01, 2020 5:24 pm
I finally replaced my USB charger by the official PSU, and I do confirm it solved my issue. Thanks.

I am just a little disappointed RPi cannot be used any more with any USB charger as it was possible with RPi 1 or 2.
Then why aren't you still using a RPi1 or 2?

I'm going to guess you want the additional performance and features of the 3B+ model, and that requires more power. The Raspberry Pi 3B+ is more than 10X faster than the old Pi1. It also has built-in Bluetooth and dual-band WiFi. All of that requires more power.

Your assumption that "RPi were to be used with any phone charger" has not been true for any Pi after the original A(+) and B(+) models (except for the Pi Zero, which has the same single-core SoC as the original models). Even with the Pi 2B it was recommended to use the official power supply (the fact they you got away with using a phone charger was just luck).

benoit_f wrote:
Sat Nov 02, 2019 10:18 pm
Can you please explain (or give me a link explaining) the differences between a charger and a power supply?
Phones do not require precise voltage control for charging (most only need a little over 4.2V to charge). Because of that, many phone chargers do not have good voltage regulation and will allow voltage to sag under load. I used to have a "5V/2.4A" charger that dropped well below 5V at only a 1A load. It charged my phone and tablet fine, but it was a lousy Pi PSU.

In addition to that, many phone chargers use a separate micro USB cable to supply power to the device, and standard micro USB 2.0 cables are not designed to deliver much more than 500mA without voltage loss. So you not only need a charger with good voltage regulation, you need a USB cable designed for higher current charging (charge cables included with high-end smart phones are often rated for 2.4A).

So are all phone chargers crap? No, some have very good regulation, and with a good micro-USB cable they work fine. The problem is, you'll never know for sure unless you can properly load-test the charger and cable, and most people don't own adjustable constant current load testers. The charger might seem to work fine, and you may be able to run your system trouble free for a long time, only to have problems later when you subject the system to higher loads than before (run more demanding software, plug in a power hungry USB device or HAT, etc.).

This is why phone chargers are not recommended as power supplies for any of the multi-core models of Raspberry Pi computers. Some may work fine, some may not, and others are just trouble waiting for the right conditions to fail. The official power supply is a proven performer that works, and is usually pretty inexpensive (depending on where you live and who you buy it from).

There are other power supplies that may work, but many so-called "power supplies" marketed for the Raspberry Pi are just re-labelled phone chargers, so again, the recommendation is to buy the official one.

The older official power supply released around the time of the Pi 2B was 5.1V/2A. The newer one for the Pi 3B and 3B+ models is 5.1V/2.5A, and the very latest one for the 4B is 3A, but that has a USB-C connector that will not fit the older models (adapters are available). I've had very good results from the RPF Universal Power supply (picture below is link), but there's also a country specific (fixed plug) model that costs less.

Image
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