@ mahjongg: I replaced the F2 fuse with a 500ma and it indeed will run a RasPi back-powered without problems.mahjongg wrote:I'm not quite sure there is a question in your post somewhere, but here are the pertinent facts.
* Current trough the PI's USB port is limited by polyfuses, which will "blow" onwards from about 140mA (depending on several factors, such as temperature and/or whether the fuse has "blown" before.
* Because of the polyfuses the USB ports are not suitable to power the PI through them
* The PI will not be damaged, when you apply unsuitable (too low) power, but it might behave erratically, and the contents and even the SD-card itself might become damaged if you do for an extended period.
* Some, but not all powered HUB's simply connect their internal 5V also to the input port, in the hope that this will also enable them to behave as unpowered hub's (which is against USB spec).
* if you power the hub, but not the PI the PI may get unsuitable low power from the hub, because of the polyfuses that are "in the way".
* One solution is to simply turn on hub an PI at the same time.
* The other solution is to power the PI from the hub, thereby "bypassing" the polyfuses, the hub must be able to deliver enough current to the PI, the PI normally needs 700mA of which 200mA is reserved for USB devices, so if you do not use USB devices on the PI (other than the hub, obviously) then 500mA should be enough, and most hubs should be able to deliver this from a single port.
I think you need to cut the red wire in the connection from RPi to USB hub so that USB hub does not attemp to back-power RPi.vinntec wrote:The bit I don't understand is what stops the hub causing trouble on its USB connection with the RPi - or does this need to have the cables cut as described elsewhere? If so, I can't find the photos that showed this very clearly anywhere - does anyone have a link if this mod is needed? If not, why not and is this an official RPi recommendation, or just current thoughts?
Thanks to all - Peter
That's very good to know, thank you!Wire cutting. The power input socket doesn't have the data pins connected, so it's not necessary to cut the data wires.
Any better indication of how to tell if my RPi is that 'latest'? A photo would be best. In my current setup I can't see the bottom side of the pcb without powering everything down and doing some disassemblyThe situation just got more complicated. The latest RPi has jumpers [...]