Powered Hubs

Here are some results i ran into when using cheap powered hub.

Initialy they may seem incompatible with th PI, but it could be due to some compromise in the design/production run to cut pricr down.

I ordered some cheap 7 port power USB hub (like 3 for $12) with the power supply included.

on my 1rst attempt i connected my PI to the hub for both power, keyboard and mouse on the hub.

The PI would start to boot and then keept on rebooting.

I removed the keyboard and mouse, no change.

The supplied power supply was rated for 5v 1A only, clearly insuficient current rating. so i used a 5v 2A supply i had left over.

I reconnected everything back, then the PI booted till it got to the USB port detection and then it was looping into the USB detection sequence. Then i noticed the micro usb plug was NOT connected on the PI ????? The PI was receiving power from the normal USB jack instead.

I then connected the micro USB plug and reapplied power, now the PI booted normaly. But the keyboard and mouse where erratics.

I decided to look inside the USB hub case and i found a jumper that connected the external power supply to the +5v side on the incoming usb connector from the PI.

Then i proceded to remove said jumper. Now the PI would not power on from the hub, good.

So i connected the micro usb cable to the powered hub along the keyboard and mouse.

now they are all behaving properly.

So my theory is that when the jumper wire was installed in the hub and you use the same hub for both power and expansions some current loops may be created inside the PI and cause some undesirable behaviour.

Here are some results i ran into when using cheap powered hub.

Initialy they may seem incompatible with th PI, but it could be due to some compromise in the design/production run to cut pricr down.

I ordered some cheap 7 port power USB hub (like 3 for $12) with the power supply included.

on my 1rst attempt i connected my PI to the hub for both power, keyboard and mouse on the hub.

The PI would start to boot and then keept on rebooting.

I removed the keyboard and mouse, no change.

The supplied power supply was rated for 5v 1A only, clearly insuficient current rating. so i used a 5v 2A supply i had left over.

I reconnected everything back, then the PI booted till it got to the USB port detection and then it was looping into the USB detection sequence. Then i noticed the micro usb plug was NOT connected on the PI ????? The PI was receiving power from the normal USB jack instead.

I then connected the micro USB plug and reapplied power, now the PI booted normaly. But the keyboard and mouse where erratics.

I decided to look inside the USB hub case and i found a jumper that connected the external power supply to the +5v side on the incoming usb connector from the PI.

Then i proceded to remove said jumper. Now the PI would not power on from the hub, good.

So i connected the micro usb cable to the powered hub along the keyboard and mouse.

now they are all behaving properly.

So my theory is that when the jumper wire was installed in the hub and you use the same hub for both power and expansions some current loops may be created inside the PI and cause some undesirable behaviour.

Yvan Turcot wrote:

 

Here are some results i ran into when using cheap powered hub.

 

...on my 1rst attempt i connected my PI to the hub for both power, keyboard and mouse on the hub.  The PI would start to boot and then keept on rebooting... Then i noticed the micro usb plug was NOT connected on the PI ????? The PI was receiving power from the normal USB jack instead.

 

I then connected the micro USB plug and reapplied power, now the PI booted normaly. But the keyboard and mouse where erratics.

 

I decided to look inside the USB hub case and i found a jumper that connected the external power supply to the +5v side on the incoming usb connector from the PI.

 

Then i proceded to remove said jumper. Now the PI would not power on from the hub, good.

So i connected the micro usb cable to the powered hub along the keyboard and mouse.

now they are all behaving properly.

 

So my theory is that when the jumper wire was installed in the hub and you use the same hub for both power and expansions some current loops may be created inside the PI and cause some undesirable behaviour.

Interesting.  I can't figure out why USB would be erratic with micro USB connected and jumper installed.  I'd put a 'scope on TP1 and see if 5V is unstable.

The behavior of your first attempt is well known: the hub powers your RasPi through polyfuse F1 or F2, depending on which RasPi host port is connected to the hub.  F1/F2 is low enough resistance to start the boot process, but when it gets underway and RasPi needs more current the resistance of F1/F2 causes RasPi's 5V plane to drop and the boot to fail.  But then the SoC's current needs drop so 5V comes back and the process repeats.

Hubs should never supply current upstream.  Some hubs use a Schottky diode to provent this, but it adds a small voltage drop if the upstream host or hub is powering the hub.  Your hub uses a mechanical solution -- I hadn't seen this before.  You obviously must install the jumper if the hub is powered from the upstream connection (bus-powered) and remove the jumper if the hub is powered from an external source (self-powered).  So as long as the hub is configured correctly (is there anything is the hub's user instructions about this?) it works fine.  

Updating this thread by vendor request, to check date sorting.

Updating this thread by vendor request, to check date sorting.

Updating this thread by vendor request, to check date sorting -082212

Updating this thread by developer request, to check date sorting.