Re: USB hubs; power; quick & dirty UPS

If would be fine if the powered hub actually powered each of the outputs with the rated USB power. Most of them don't.

A typical powered hub has barely enough power for a Pi, so when you connect other devices that require power as well you will normally run into trouble when you power the Pi from the hub.

Is that a problem with the hub or with the PSU for the hub? After all a 5 port USB hub ought to have a PSU capable of at least 2.5A without breaking sweat. How many hubs come with such a power supply?

A typical Chinese no brand powered hub just joins all the 5v and ground traces together to the input jack socket because a current limited switch costs money :) In that case current is limited by what the wall wart can deliver!

On Tue, 10 Sep 2013 12:00:31 +0100, Adam Funk wrote in :

Take a look at this article, and read the Comments section for other alternatives:

Yes. Just connect the down-link to the Pi and a standard usb to µUSB cable from the hub to the power in on the Pi.

Some hubs send power up the down-link wire too - in that case you can power a Rev 2 Pi from the USB port and save the extra cable.

The usual warnings about the power to the Pi no-longer being protected via the polyfuse, etc. apply.

Yes. You need a low-loss regulator, or a standard 7805 if you don't mind (a) burning yourself on the heatsink and (b) wasting batterys.

You also need some wizardry to do the switch over and stop one back-powering the other.

Gordon

Not many. Typically the power supply is 1A.

On Tue, 10 Sep 2013 14:30:14 +0100 (BST), "Dave Liquorice" declaimed the following:

The common USB specification is for only 0.5A distributed among all ports on a hub. One port eating it all, or four ports with 0.125A, or some combination in between.

There is now a specification for "charging ports", but they tend to only provide high current when the source device is "off" (no data flow). I've also seen a few devices with 1A ports (mostly on HDTVs for use in running slide-shows from USB powered hard drives)

ICBW but isn't that specification for a passive hub? I'm pretty sure that powered hubs are specified for 500mA per port or a total loading limited by its wall wart psu if that isn't rated for the totalnumber of ports times 500mA.

The modern laptop sized drives, despite their claimed lower current consumption tend to be far more problematic than their ancient counterparts (with current ratings sometimes as high as an amp) which worked without any bother when used in usb enclosures. The PR departments seem to have far too much influence on the drive labelling these days.

Correct but even worse passive (unpowered hubs) was 0.5A max from upstream to power the hub AND all the ports.

Powered hubs, if they wanted could take 0.5A from upstream and supply

only

Standards and interpretations by PR/Marketing departments and others has always been a 'joy'.

I picked up a Belkin 4-port hub recently (at Tesco of all places) - psu claims to be rated at 2.5A, and I've run both the pi and a dvd player (haven't tried writing yet). All of a tenner's worth of impulse buy.

The "LOGIK" one I got from PC world has a 2A PSU and it powers 2 Pi's without any issues, so it seems there is a huge variance.

Gordon

Interesting, thanks.

In other words, reinvent the laptop power supply, more or less, with

This one?

Indeed.

Thanks to everyone who replied for the interesting points.

That's the one. Had it since day 1 and it's still going strong.

Yes, it "back-powers" the Pi - which for me in the early days wasn't an issue as I was connecting a regular usb to micro usb cable from the hub to the Pi - as well as the link cable, not really an issue at all. On the Rev 2 Pi's I have, they power directly from the link cable without the additional "power" cable. (Rev 1's have 140mA polyfuses to limit the current through the USB ports)

I use it to power 2 Rev 2 Pi's ('headless') via their USB sockets.

Gordon