peripherals needing powered hubs

[geffers]

Folks,

I've read that some TV tuners need a powered USB hub to work.

Why would this be? If the PSU can supply the amps why would the tuner require a powered hub?

Geffers

[klricks]

Folks,

I've read that some TV tuners need a powered USB hub to work.

Why would this be? If the PSU can supply the amps why would the tuner require a powered hub?

Geffers

Depends on which RPi version you are referring to.

For B Rev 2 there is a input 'polyfuse' which limits the total current of RPi + GPIO + USB devices to 750mA
(The early B rev1 also had fuses on the USB ports which limited output to 120mA or so each port).

The input fuse on B+ is rated 2A. In addition the B+ has USB power controller which will give a maximum output of 1.2A to the USB ports (combined). So 1.2A for USB port(s) + 0.8A for RPi + GPIO.

If you attempt to draw more current than the fuses can handle then the RPi will become unstable........... Brownouts.... Crashes.... rebooting etc.... The USB devices are the first to suffer when power is not sufficient.

I have no idea the power requirements of a TV tuner? But many devices such as USB hard disks which could not run on a B without a powered HUB can run OK on a B+ or RPi2.

[ktb]

I don't know about tv tuners either. My guess is that a powerful one will require external power.

My dual band WiFi adapter will only work correctly on 5 GHz if powered by an external hub with my B+ (even with max_usb_current=1, 5 GHz doesn't work directly). It will do 2.4 GHz fine directly from the Pi.

[Redfez]

If you are getting a powered USB hub then make sure you get a decent one. I've seen tear downs of some of them and the insides of some of them are shocking, if not downright dangerous for the Pi or any other equipment hooked up to them (all sorts of shorts, damaged wires, etc). A lot of them seemingly look flash on the outside but are the cheapest garbage inside. Hopefully some of the folk here can recommend some good ones out there that are safe and capable of being up to the job.

[geffers]

Folks,

I've read that some TV tuners need a powered USB hub to work.

Why would this be? If the PSU can supply the amps why would the tuner require a powered hub?

Geffers

Depends on which RPi version you are referring to.

For B Rev 2 there is a input 'polyfuse' which limits the total current of RPi + GPIO + USB devices to 750mA
(The early B rev1 also had fuses on the USB ports which limited output to 120mA or so each port).
.

Thank you for good explanation.

Geffers

[geffers]

I don't know about tv tuners either. My guess is that a powerful one will require external power.

My dual band WiFi adapter will only work correctly on 5 GHz if powered by an external hub with my B+ (even with max_usb_current=1, 5 GHz doesn't work directly). It will do 2.4 GHz fine directly from the Pi.

I'm thinking it is probably the firmware as it doesn't work either on my Ubuntu laptop running 14.04.

Geffers

[geffers]

Thanks for advice. I'll get one from a proper Pi retailer.

geffers

If you are getting a powered USB hub then make sure you get a decent one. I've seen tear downs of some of them and the insides of some of them are shocking, if not downright dangerous for the Pi or any other equipment hooked up to them (all sorts of shorts, damaged wires, etc). A lot of them seemingly look flash on the outside but are the cheapest garbage inside. Hopefully some of the folk here can recommend some good ones out there that are safe and capable of being up to the job.