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eriktheitalian
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About Rpi2 usb power output (0.6Amp/1.2Amp switch)

Wed Mar 04, 2015 12:21 am

I'm added some switches to config.txt
They are:

"max_usb_current=1
safe_mode_gpio=4"

I'm using 1.2Amp usb power output now. I need information about disadvantages.
My power supply 2.0Amp.
is 0.8Amp enough for Rpi2 without usb ?
I cant using enough English language. My writings can be wrong grammer.$
"in micro$oft we not trust"

klricks
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Re: About Rpi2 usb power output (0.6Amp/1.2Amp switch)

Sat Mar 07, 2015 3:16 pm

eriktheitalian wrote:I'm added some switches to config.txt
They are:

"max_usb_current=1
safe_mode_gpio=4"

I'm using 1.2Amp usb power output now. I need information about disadvantages.
My power supply 2.0Amp.
is 0.8Amp enough for Rpi2 without usb ?
Use max_usb_current=1 only. The safe_mode command is obsolete, redundant and not needed.
The power setting for 1.2A is the maximum current allowed through all 4 port combined. The current actually used is of course determined by the USB devices themselves which can be UP TO 1.2A total.
The maximum power allowed into the RPi is limited to 2A by the fuse (F1) so if your USB devices draw 1.2A, then that leaves 0.8A for the RPi + GPIO.
If the USB devices use 1A then that leaves 1A for the RPi + GPIO...... etc

There is no disadvantage with using the 1.2A setting as long as you have a good quality 2A power supply.
0.8A is plenty, the RPi probably uses about half that..
Go here for my RPi writeup. Basic config, Serial Port add-on etc:
http://blackeagle12.net/Comp/RPi/Rpi.html Click contact icon then world icon --->

shadowofdarkness
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Re: About Rpi2 usb power output (0.6Amp/1.2Amp switch)

Sat Mar 07, 2015 7:30 pm

Is that true about the pi only allowing 2a in? Lucky I didn't finalize my payment yet but I was just about to buy a 5v 3.5a charger with a fixed cable for less loss. But now I'll stick with my 5.3v 2a one. If the extra amps will not actually help when I use max USB current I'll stick with the better volts.

klricks
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Re: About Rpi2 usb power output (0.6Amp/1.2Amp switch)

Sat Mar 07, 2015 8:28 pm

shadowofdarkness wrote:Is that true about the pi only allowing 2a in? Lucky I didn't finalize my payment yet but I was just about to buy a 5v 3.5a charger with a fixed cable for less loss. But now I'll stick with my 5.3v 2a one. If the extra amps will not actually help when I use max USB current I'll stick with the better volts.
Yes the input fuse F1 is a special self resetting type of fuse often called a 'polyfuse'. If more than 2A is allowed to enter then the fuse heats up and resistance begins to increase causing the voltage to drop. Above a certain point the fuse totally chokes off the voltage. The fuse if tripped will reset itself if left powered off for several hours.
Since the B+ and 2B now have a USB power control limiter, the only time you run into 'polyfuse' trouble is when using too much power by connections made to GPIO's. (If more than 1.2A is pulled by USB devices, then they may become unstable or crash but the system should remain stable in most cases).

The B model would crash if USB devices used too much power or you attempted to 'hot plug' a USB device etc. The input fuse on the B is only 750mA and was directly connected to the USB ports without control.
Go here for my RPi writeup. Basic config, Serial Port add-on etc:
http://blackeagle12.net/Comp/RPi/Rpi.html Click contact icon then world icon --->

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FTrevorGowen
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Re: About Rpi2 usb power output (0.6Amp/1.2Amp switch)

Sat Mar 07, 2015 9:28 pm

shadowofdarkness wrote: ... I was just about to buy a 5v 3.5a charger with a fixed cable for less loss. But now I'll stick with my 5.3v 2a one. If the extra amps will not actually help when I use max USB current I'll stick with the better volts.
Unfortunately there's no guarantee that a charger labelled 5.3V 2A is any better (or worse) than one labelled 5V 3.5A - generally all the label means is that they may supply 5 or 5.3 V and 3.5A or 2A but not necessarily at the same time.
FWIW, you may be interested in the load characteristics of quite a few PSUs or chargers that I've measured:
http://www.cpmspectrepi.webspace.virgin ... plies.html
http://www.cpmspectrepi.webspace.virgin ... dPSUs.html
Trev.
Usually running Raspbian Jessie on up to 12 of 13 Pi's (an A, B1, 2xB2, 2xB+, A+, P2B, 3xP0, P0W) and Stretch on my P3B. See: https://www.cpmspectrepi.uk/raspberry_pi/raspiidx.htm

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eriktheitalian
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Re: About Rpi2 usb power output (0.6Amp/1.2Amp switch)

Mon Mar 09, 2015 11:07 am

Thanks for important knowledge. I'm realy satisfied. Maximum power input is limited for 2amp. 5v with 2amp supporting can be not possible at same time from power supply.

I'm understanding some power supplies supporting system like 5v or 2amp. Some 5v with 2amp.

I cant easily prepare power test unit. But i can try pi2's maximum overload ( without overclock ). Like overclock stress test. I can do stress test load for all SOC units at same time. I need same for usb devices at same time. ( default raspberry pi2 + 2 max 0.5 amp usb device ). And, i can wait for rainbow square.

I'm only facing "rainbow square at bottom left" when usb hot-plugging.(main micro usb power plug sensitive for moving card). But im not realy care. Pi2 pretty stable. Never randomly locking.
Last edited by eriktheitalian on Mon Mar 09, 2015 11:11 am, edited 2 times in total.
I cant using enough English language. My writings can be wrong grammer.$
"in micro$oft we not trust"

Baguda
Posts: 7
Joined: Tue Sep 15, 2015 3:43 pm

Re: About Rpi2 usb power output (0.6Amp/1.2Amp switch)

Sun Jun 05, 2016 4:57 pm

Hello Pi Community!
I am using a Pi 3 which is fused to 2.5A. However, I am planning on powering the unit via the GPIO 5V pins, which should power the whole 5V rail. I am using a regulated and protected 5.0V 5A supply. I want to be able to power at least two "high power" usb devices (>500mA), as well as two low power devices. Seeing how the GPIO 5V pin bypasses the 2.5A fuse, I am wondering if the full 5A capability of the power supply will be made accessible to the USB devices. I am not planning on pulling in excess of 3A peak, however, I am curious if operating the pi in this manner would be harmful to any of the on-board hardware.

gregeric
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Re: About Rpi2 usb power output (0.6Amp/1.2Amp switch)

Sun Jun 05, 2016 5:18 pm

You may have bypassed the polyfuse when powering via GPIO, but you have not bypassed the USB current limit switch. Your USB devices will still be limited to 1.2A nominal across all four ports on the Pi3. If you must have more, then you can modify the AP2553 USB current limit switch with a lower value of Rlim

MAHAD93
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Re: About Rpi2 usb power output (0.6Amp/1.2Amp switch)

Mon Oct 24, 2016 3:53 am

And, How would one go about doing that ?

klricks
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Re: About Rpi2 usb power output (0.6Amp/1.2Amp switch)

Mon Oct 24, 2016 5:13 am

MAHAD93 wrote:And, How would one go about doing that ?
Read Page 10 of the data sheet: http://www.diodes.com/_files/datasheets/AP255x.pdf
Note the USB limit chip is U13 and the ILIM resistor on pin 5 is R50, located near GPIO pin 39.

Changing to a higher current however would defeat the purpose of the USB limiter which is to keep the rest of the RPi from brownout and crashing when USB device(s) use too much current.
Also the traces may not be able to handle higher current if a single high current USB device is used.
Go here for my RPi writeup. Basic config, Serial Port add-on etc:
http://blackeagle12.net/Comp/RPi/Rpi.html Click contact icon then world icon --->

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