jets
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How much power can Rpi throughput to USB?

Sat Dec 14, 2013 5:26 pm

I was sure this has been dealt and written a lot in forums, but either I was not good enough googler or something else.

I have a 3A power supply powering the Rpi. Of course, the 3A is plenty for Rpi. However, I am wondering, if I could power 3G Dongle and some other stuff from Rpi USB-ports? I mean, how much power does Rpi put through to USB? What is maximum?

I have a 930Ah battery bank at my off-grid cottage, where I run one Rpi taking care of number of functions. The PSU I use is a step-down PSU that is directly connected to 12V battery bank and puts power to singe USB which is connected to RPI via standard cable.

Now I power everything else by use of Inverter. I'd like to remove the inverter from the system when I am not on-site. Hence, it would be nice if I could power up 3g dongle, 1-2 usb-cameras and some other low power stuff by use of Raspberry Pi's USB.

So, how much is the max power Rpi can throughput to USB?

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redhawk
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Re: How much power can Rpi throughput to USB?

Sat Dec 14, 2013 5:34 pm

It doesn't matter if you have 100Amps powering the Pi there is a polyfuse (F3) that limits current consumption to roughly 750mA tops.
If you need to connect power hungry devices like USB hard drives then an externally powered USB hub is highly recommended.

Richard S.

jets
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Joined: Mon May 06, 2013 9:40 am

Re: How much power can Rpi throughput to USB?

Sat Dec 14, 2013 5:51 pm

redhawk wrote:It doesn't matter if you have 100Amps powering the Pi there is a polyfuse (F3) that limits current consumption to roughly 750mA tops.
If you need to connect power hungry devices like USB hard drives then an externally powered USB hub is highly recommended.

Richard S.
Aha. Thanks. But is it 750mA tops per USB or both USB's RPi has together?

I will now consider on some sort of USB-divider to power up a USB hub, which would then power and have all other stuff.

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rpdom
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Re: How much power can Rpi throughput to USB?

Sat Dec 14, 2013 6:02 pm

jets wrote:But is it 750mA tops per USB or both USB's RPi has together?

I will now consider on some sort of USB-divider to power up a USB hub, which would then power and have all other stuff.
It is 750mA total including the Pi itself, both USB ports, and any GPIO pins used. In practice you can get about 100mA on each USB port, or 200mA if you only use one of them (more on the model A's single USB port, probably about 400mA)

jets
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Re: How much power can Rpi throughput to USB?

Sat Dec 14, 2013 6:06 pm

rpdom wrote:
jets wrote:But is it 750mA tops per USB or both USB's RPi has together?

I will now consider on some sort of USB-divider to power up a USB hub, which would then power and have all other stuff.
It is 750mA total including the Pi itself, both USB ports, and any GPIO pins used. In practice you can get about 100mA on each USB port, or 200mA if you only use one of them (more on the model A's single USB port, probably about 400mA)
Oh. I have the B-model(s). Well, better direct myself to dividing the USB-cable from the PSU.

Thanks!

Btw, Should I have been able to find all this out by myself someway? I tried googling with all sorts of words and combinations..

EDIT: Corrected that I have B-model Rpis, not A.

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rew
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Re: How much power can Rpi throughput to USB?

Sun Dec 15, 2013 10:00 pm

Just power the USB hub from a 12V -> 5V stepdown regulator. Then connect things up. If you use a sturdy enough cable to the hub, the hub will reverse-power the raspberry pi!


(I'm powering a hub from a 5V 60A powersupply and the 'pi from there...) :-)
Check out our raspberry pi addons: https://www.bitwizard.nl/shop/

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mahjongg
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Re: How much power can Rpi throughput to USB?

Sun Dec 15, 2013 11:40 pm

jets wrote: Btw, Should I have been able to find all this out by myself someway? I tried googling with all sorts of words and combinations..
what about reading the FAQ?
http://www.raspberrypi.org/faqs#powerReqs

or the wiki.
http://elinux.org/RPi_Hardware#Power

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