[Scandalous Ion Cannon]

I just bought a USB 2.0 hub that is POWERED and I was rather shocked to find out that if the computer is off it doesn't charge the shuffle. I would have thought that if the hub is powered it would always pump power through.

Is this a problem with just this hub or do they all act like this?

Firewire doesn't have this problem.

[ghporter]

I agree that it seems odd. My understanding is that a powered hub, with its own separate power supply, should provide +5V whether there's data or not. I think in your place I'd take the hub back to where I got it and see if others do the same thing.

Maybe there's something about iPods not charging if they aren't getting data?

[Scandalous Ion Cannon]

Originally Posted by ghporter

I agree that it seems odd. My understanding is that a powered hub, with its own separate power supply, should provide +5V whether there's data or not. I think in your place I'd take the hub back to where I got it and see if others do the same thing.

Maybe there's something about iPods not charging if they aren't getting data?

Even if you eject an ipod from your computer port though itunes it still charges.

I just want to know if anyone else has this problem or can recommend a brand.

[tooki]

Power draw on USB is supposed to be highly controlled. No USB device is supposed to draw power without first getting permission from the host computer. If the computer is off, the iPod can't get permission from the computer, and won't draw power.

Presumably, the iPod has some way of detecting whether it's connected to a USB bus (even one that's off) or to the AC adapter.

tooki

[Scandalous Ion Cannon]

Originally Posted by tooki

Power draw on USB is supposed to be highly controlled. No USB device is supposed to draw power without first getting permission from the host computer. If the computer is off, the iPod can't get permission from the computer, and won't draw power.

Presumably, the iPod has some way of detecting whether it's connected to a USB bus (even one that's off) or to the AC adapter.

tooki

So the simple answer is this is total normal behaviour that I am experiencing.

Damn I miss firewire.

[Diggory Laycock]

Originally Posted by Scandalous Ion Cannon

Damn I miss firewire.

Don't we all - My Powerbook looks rubbish with a PC-Card USB 2.0 thing poking out the side

[tooki]

Originally Posted by Scandalous Ion Cannon

So the simple answer is this is total normal behaviour that I am experiencing.

Well, it's the consequence for USB being able to tell you that the reason it can't run a device is because not enough power is available. FireWire can't do that -- if something's drawing too much power, it'll just malfunction. (Though I feel compelled to point out that the FireWire spec requires far more power be available on a 6/9-pin jack than USB can provide.)

tooki

[Scandalous Ion Cannon]

So I am guessing there is no hub that allows charging when the computer is off then?

[tooki]

It's not up to the hub to decide -- it's providing the power already, but it's up to the device to start drawing power once it has permission.

tooki

[ghporter]

Does that mean that the Apple-provided AC adapters are somehow signaling iPods to charge? I wonder how.

[itguy05]

Not sure.

I have an APC TravelPower case I use with my IBM Thinkpad (work computer). It has a USB port on the brick that allows you to charge cellphones, Palms, and other PDA's. It works great for my SE T637 and my Palm. I doubt it has smarts in it to tell those devices to charge.

In addition, my cellphone's USB charging cord seems to be nothing more than a wire from 2 pins on the USB bus to the proper pins on the phone.

Also, when building PC's (yes, I did that too) and hooking up a front panel USB port, you typically had 4 wires: Data +, Data -, +5VDC and ground. I have this feeling the +5DC is always available to devices. What may be happening is the iPod's circuitry won't charge until it can communicte with the USB bus.

[tooki]

As I already said, the power is there already.

Here's how USB is supposed to work (simplified, but a more or less accurate mental model):

1. You plug in a gadget.
2. The gadget draws just a tiny bit of power -- just enough to turn on its USB interface -- and declares to the computer "I am GadgetX! I need 500mA of power."
3. The computer talks to the USB controller and figures out if enough power is available.
4. a. If too little power is available, the computer tells the gadget "Sorry, buddy! Not enough juice to go around, you'll have to stay off! Come again!" and puts a message on the computer screen saying that the device could not be used because not enough power is available.
4. b. If enough power is available, the computer tells the gadget "A-OK! There's enough power, go ahead and power up!" and the computer load's the device's driver and lets it do whatever it does.


As I said, the power is there, but gadgets are only supposed to draw significant amounts of power once they have gotten permission to do so.

Because the power is always there, many USB charging cords for phones, etc, simply violate USB convention and draw power without asking. This has become common enough that it's almost a quasi-standard now.

AFAIK, USB hubs do link up with devices that are plugged into them (even if no computer is present). My hunch is that when the iPods link up with a USB bus, they follow the USB standard, and if they just detect power but no USB bus, they go ahead and charge.

tooki

[ghporter]

Originally Posted by tooki

AFAIK, USB hubs do link up with devices that are plugged into them (even if no computer is present). My hunch is that when the iPods link up with a USB bus, they follow the USB standard, and if they just detect power but no USB bus, they go ahead and charge.

That would follow Apple's habit of sticking to standards as much as possible, and it's both a simple and an "elegant" solution. ("Elegant" in computer design and programming usually means a combination of "clever" and "easy to do." )

[cindyding0412]

I have to say that it is strange,
I use hub my self,but never met such problem!

[Scandalous Ion Cannon]

Originally Posted by cindyding0412

I have to say that it is strange,
I use hub my self,but never met such problem!

Might help if you told us what hub that is and how you have things hooked up.

[teknoman]

I have a powered Belkin hub, and I use it to charge my iPod shuffle. And it definitely works with my computer off.

Here's a link to the hub I have, I got it for around $30 online:
http://catalog.belkin.com/IWCatProdu...duct_Id=158910

[analogika]

Originally Posted by tooki

Well, it's the consequence for USB being able to tell you that the reason it can't run a device is because not enough power is available. FireWire can't do that -- if something's drawing too much power, it'll just malfunction. (Though I feel compelled to point out that the FireWire spec requires far more power be available on a 6/9-pin jack than USB can provide.)

Which of course compels me to remind you of the SLEW of Powerbooks and iMacs that needed a farking MOTHERBOARD REPLACEMENT because Apple didn't comply with their own ****ing specs and spiking Firewire power would simply blow out the Firewire chipset on the logic board.

Happened twice to my gumdrop iMac with two different bus-powered hard drives, and three times in a row to my friend's tiBook with a Firewire audio interface, after which he walloped Apple into getting a new Powerbook where the issue had finally been fixed - three years after my iMac was produced.

[tooki]

I'm pretty sure that problem is more complex than you make it out to be.

tooki