fosslinux
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Joined: Sat Apr 13, 2019 1:45 am

questions about max_usb_current=1

Sat Apr 13, 2019 1:54 am

Hi!

I have a portable hard drive attached to my raspberry pi. At intermittent times, when writing and drawing the most power, it will suddenly fall off the system. Every error I have found related to it is power problems. The PSU seems to be fine, the specs are:

INPUT: 100-240V ~ 50/60Hz 0.5A
OUTPUT: +5.1V - 2.5A

It seems to be specially designed for raspberry pi, it has a raspberry pi symbol on the front.

I saw the config.txt option

Code: Select all

max_usb_current=1
, which seems to be the solution I am looking for.

I've got a few questions about this option:

1. Is there any chance it could fry my pi/a port/my external hard drive?
2. Is it reversible?
3. Are there any cautionary actions I should take?
4. Any other caveats?

Thanks,

~fosslinux

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HawaiianPi
Posts: 4206
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Location: Aloha, Oregon USA

Re: questions about max_usb_current=1

Sat Apr 13, 2019 7:51 am

Is your power supply this one: https://www.raspberrypi.org/products/ra ... er-supply/ ?

What model Pi?
What make/model/size hard drive?
Are you booting from the HDD or just using it as storage?
What kind of cable connects the HDD to your Pi, and is it the cable that originally came with the drive?
Can the drive be externally powered (does it have a power jack)?

EDIT: max_usb_current=1 is the default now (putting that in config.txt has no effect).
My mind is like a browser. 27 tabs are open, 9 aren't responding,
lots of pop-ups...and where is that annoying music coming from?

fruitoftheloom
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Location: Delightful Dorset

Re: questions about max_usb_current=1

Sat Apr 13, 2019 7:54 am

adieu

My other Computer is an Asus CS10 ChromeBit running Chrome Operating System.
HP Envy 4500 Wireless Printer supported by HPLIP software in Raspbian Buster.
Raspberry Pi Model 2B v1.1

fosslinux
Posts: 3
Joined: Sat Apr 13, 2019 1:45 am

Re: questions about max_usb_current=1

Sat Apr 13, 2019 8:40 am

sure is, but in black
What model Pi?
Pi 3B (not the 3B+)
What make/model/size hard drive?
Segate Expansion 2TB, 5400rpm
Are you booting from the HDD or just using it as storage?
using as storage
What kind of cable connects the HDD to your Pi, and is it the cable that originally came with the drive?
just the one that came with the drive
Can the drive be externally powered (does it have a power jack)?
no
EDIT: max_usb_current=1 is the default now (putting that in config.txt has no effect).
oh, maybe i'm out of luck.

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procount
Posts: 1651
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Location: UK

Re: questions about max_usb_current=1

Sat Apr 13, 2019 9:45 am

You could plug your HDD into an externally powered USB hub to power it, but make sure the hub will provide sufficient power for it.
Some USB cables for HDDs have 2 USB plugs: one is power+data, the other is just for power so that you can draw the max current from 2 ports instead of just one.
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klricks
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Re: questions about max_usb_current=1

Sat Apr 13, 2019 12:55 pm

procount wrote:
Sat Apr 13, 2019 9:45 am
You could plug your HDD into an externally powered USB hub to power it, but make sure the hub will provide sufficient power for it.
Some USB cables for HDDs have 2 USB plugs: one is power+data, the other is just for power so that you can draw the max current from 2 ports instead of just one.
Using a dual USB cable will have no benefit when used on a RPi.
The 5V USB power to all 4 ports are wired together in parallel. So if a USB device draws 1A with one cable then with 2, the current will be split equally between the 2 (not doubled). 0.5A + 0.5A = 1A total.... The result is the same.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

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procount
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Location: UK

Re: questions about max_usb_current=1

Sat Apr 13, 2019 1:27 pm

Yes, sorry I should have been clearer that I was still talking about use with a hub. Thanks for clarifying for the OP.
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drgeoff
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Re: questions aboutIu max_usb_current=1

Sat Apr 13, 2019 3:38 pm

Using both cables with a RPi will reduce the voltage drop through connectors and cables but in virtually all cases the change will be negligible and yield no practical benefit.

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HawaiianPi
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Re: questions about max_usb_current=1

Sat Apr 13, 2019 6:55 pm

So, official PSU on a 3B with a Seagate 2TB external HDD connected with its OEM cable. That should work. The Raspberry Pi 3B can output up to 1.2A from it's 4 USB ports, with no per-port limits (all 1.2A can come out of 1 port if no others are in use).

Seagate drives are power pigs, but 1.2A should drive even a USB 3.0 HDD (900mA).

Do you have any other power hungry accessories (HAT, backlit keyboard)? What else is connected to your Pi 3B?
My mind is like a browser. 27 tabs are open, 9 aren't responding,
lots of pop-ups...and where is that annoying music coming from?

fosslinux
Posts: 3
Joined: Sat Apr 13, 2019 1:45 am

Re: questions about max_usb_current=1

Sun Apr 14, 2019 5:52 am

Firstly, my apologies, it's actually not the OEM cable. I'll try to find it after I'm back from holidays (this Thursday).

No, I don't have any other power hungry devices; only another hard drive in a powered enclosure.

Sorry if this wasn't made clear, but the vast majority of the time it works fine. It's only after it's been continuously writing for 6 hours plus that it fails out. It works fine on other devices.

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