flautze
Posts: 3
Joined: Thu Oct 19, 2017 2:37 pm

USB not detected with VCC pin taped and active hub. Normal?

Sun Jan 13, 2019 12:17 am

Hello,
Before I describe my problem here is an overview of the setup I want to run.

Pi Model 3B+.
Official PI power supply feeds active 4 port USB Hub.
The USB Hub is hooked up to the Pi (top right port).
1 of the HUB ports goes into USB-SATA converter with 2.5 HDD.
Second HUB port goes via MicroUSB cable to power port of Pi.

First issue I experienced was that afer shutdown I unplugged the Power of Pi, but red LED remained lit. Ok it seems my Hub feeds back. I read a lot about that and wanted to remove this 'issue'.
Instead of cutting the red line in the USB I used tape to cover the right pin in the plug (VCC).

After then again powering up the setup the Pi does not recognize any USB devices hooked up to the Hub.
Neither the HDD nor a Logitech Unifying dongle. When I plug those directly into thePi, no problem.

So now I have removed the tape, everything works normal. Since I now used the top left port suddenly the red LED is not turned on anymore after I shut down my Pi... what the heck? (2nd isue).

How can that be? Maybe someone can explain/help.

What do I want to achieve? Use the current Hub with HDD without backpowering...

Thanks and Best regards.

hippy
Posts: 5607
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: USB not detected with VCC pin taped and active hub. Normal?

Sun Jan 13, 2019 12:21 am

flautze wrote:
Sun Jan 13, 2019 12:17 am
Instead of cutting the red line in the USB I used tape to cover the right pin in the plug (VCC).
Which exactly is the "right pin" of a USB plug ?

That depends on which way it's pointing, which way up it is. I suspect you might have insulated out the 0V pin. Or perhaps the insulation meant other pins were not making good contact.

W. H. Heydt
Posts: 10611
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: USB not detected with VCC pin taped and active hub. Normal?

Sun Jan 13, 2019 6:14 am

I have yet to see a USB hub that I would trust to power a Pi3B. Even the ones that have a "high power"/"charging" port usually won't provide the kind of current a Pi3B will need.

I'm also curious how you power a hub with the RPF PSU. I don't recall seeing any hubs with a micro-B connector. Plus, normal power allocation from a hub is 500mA per port, and at 2.5A, the RPF PSU isn't going to have enough power to provide that *and* power a Pi3-class board. To do that, you'd really want at least a 4A power supply. (2.5A to the Pi, 500mA for each of the other three ports.)

flautze
Posts: 3
Joined: Thu Oct 19, 2017 2:37 pm

Re: USB not detected with VCC pin taped and active hub. Normal?

Sun Jan 13, 2019 9:06 am

I am using this Hub.
https://www.amazon.de/CSL-Verteiler-Ult ... sb+3.0+hub

It comes with microUSB power.
I ham not using the accompanying PS (2A), but the 2.5 A.
The description even states that it protects host PC from back current, but my experience tells me otherwise.

Runs fine with HDD connected + Pi. Well actually I am not sure. HDD goes into readonly mode several times.
I might just try hooking up both independently, but then I would want to make sure there is no backpower...

Which brings me back to my original problem. Why does the Pi not recognize the devices (powered from Hub with isolated VCC to Pi)?
Only thing I could think of is that the Hub does not (activate the ports if the VCC is not connected... does that mamesense?)

Edit: by the way I taped VCC pin according to this layout, so when the Hub is plugged into Pi the tspe is on the RJ45 port side.
http://md380.blogspot.com/2015/06/tyter ... m.html?m=1

BR,
Flautze

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