TeaAddict
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will non-powered USB hub work?

Tue Dec 18, 2012 7:59 pm

Hello I was wondering since the 100mA limit on the USB has been lifted, will a non self powered USB hub work? I am using a power supply capable of up to 1.8A, and although that wont power much on a non powered USB hub, it should have more than enough power for a keyboard and WiFi adapter. Will this work?
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Burngate
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Re: will non-powered USB hub work?

Wed Dec 19, 2012 11:19 am

Possibly.
But using a non-self-powered hub means that all the current required by the devices, including the WiFi adapter which is the most power-hungry, has to come through the poly-fuse on the input of the Pi.
Since that poly-fuse is only rated at ~700mA, and the Pi itself takes most of that, there's not much left for devices.

Also, if you try hot-plugging the WiFi adapter, you may find the inrush current to it may cause a reboot of the Pi

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Re: will non-powered USB hub work?

Wed Dec 19, 2012 11:36 am

I thought there still was a maximum power that the Pi would deliver of 100mA through each of it's USB ports. Isn't that still true? If so, then the answer to your question depends on how many mA is required by each device plugged in to the hub, as well as how much is required by the hub itself.

If the units do not say how many mA they use, not sure how you can find that out. I am running into the same issue, although the addons are different, concept is the same.
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Burngate
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Re: will non-powered USB hub work?

Wed Dec 19, 2012 5:32 pm

sdjf wrote:I thought there still was a maximum power that the Pi would deliver of 100mA through each of it's USB ports. Isn't that still true? ...
The original Pi had a poly-fuse in line with each USB socket, severely limiting the current available for devices. Later revisions removed those poly-fuses, so that the current limit is more relaxed on those.
There's still the input poly-fuse, so powering normally, you can't provide much current to devices.

But feeding power through the GPIO pins bypasses that poly-fuse, so you could use a non-powered hub with that should probably work.

The ideal is to use a powered hub and back-feed the Pi from it.

TeaAddict
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Re: will non-powered USB hub work?

Thu Dec 20, 2012 4:04 am

Thank you all for your response!

How would this (https://www.sparkfun.com/products/114) be for powering the Raspberry Pi through the GPIO?
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Re: will non-powered USB hub work?

Thu Dec 20, 2012 10:52 am

Hmm.
It uses a linear regulator, which just wastes power to keep the output constant.
If you feed it with, say, 12v, and your Pi is taking 1A at 5v, then the other 7v is dropped across the regulator, and that 1A is passing through it.
That's 7w, and it'll get very warm. It will probably want a heatsink to keep it in the land of the living.

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