Powered HUB feeds RasPi?

[charlesanjos]

Hi. Since it was recommended to acquire a powered hub, i went and did it. But something funny happens when I connect the powered hub to a RasPi's USB port: it turns on! That i wasn't expecting!
Is this normal?
So if I have a 1A PSU powering my Pi via default source and a Powered USB Hub also with a 1A PSU connected to it via USB, theoretically my Pi is receiving 2A?
Would 2A be sufficient to hold a Pi with LAN, a WLAN adapter and a keyboard? Each USB port outputs 500mA power right?

[calebzulawski]

Are you saying the Raspberry Pi turns on, or the USB hub? I wouldn't be totally surprised if a powered USB hub's indicator light showed that the port was "powered" when it really wasn't, it would be drawing the current from the Raspberry Pi's USB ports, which is much less than the 1A the hub is rated at. Also, no matter what the power supply is rated at, the onboard USB ports have polyfuses limiting the current (140mA sounds right off the top of my head, but it could be more). The RPi will only draw whatever the main board is drawing, plus whatever the onboard USB is drawing, which is at most the rating of those polyfuses (which overall should be significantly less than 1A)

[bursar]

It seems to be a known problem with some hubs that they backfeed power to the Pi. The suggested solution seems to be to open up the USB cable that runs between the hub and the Pi and the snip the wire that provides voltage (I believe it's the red one - but double check before attacking the cable!).

[calebzulawski]

Also, regarding your question, the RPi's onboard ports would be able to handle a keyboard and LAN just fine on 1A. A USB wifi card should work fine as well (assuming it is compatible: see http://elinux.org/RPi_VerifiedPeriphera ... i_Adapters). Just make sure the USB wifi card is plugged into the powered hub, as it will draw more power than the RPi can handle, but the USB hub will be able to handle it fine.

[charlesanjos]

It seems to be a known problem with some hubs that they backfeed power to the Pi. The suggested solution seems to be to open up the USB cable that runs between the hub and the Pi and the snip the wire that provides voltage (I believe it's the red one - but double check before attacking the cable!).

Thanks for the tip man. Think that it could generate some sort of energy anomaly, like consuming more power from the Pi if it is already powered by it's own PSU?

Also, regarding your question, the RPi's onboard ports would be able to handle a keyboard and LAN just fine on 1A. A USB wifi card should work fine as well (assuming it is compatible: see http://elinux.org/RPi_VerifiedPeriphera ... i_Adapters). Just make sure the USB wifi card is plugged into the powered hub, as it will draw more power than the RPi can handle, but the USB hub will be able to handle it fine.

Thanks for the info. I'll keep experimenting.