Charging USB Devices via HUB with no host

[ratzlaff]

I have a few devices that I want to charge every night. I don't like using a lot of wall warts plugged into a power strip. I recently had the epiphany that I could use a powered USB hub as a 'usb power strip'. I just have one wall wart and I can charge multiple devices at once without clogging up my power strip.

I ran into some issues though.

When I don't have a host (PC) connected to the USB hub my devices will only charge with a 'power only' usb charging cable. But if I use a standard usb cable that can be used for data, I do not charge. Well that is not entirely true. I get a trickle...my phone doesn't even say that it is charging, but my power meter says that it is consuming about 1W...maybe less like 0.7W. Well under the 8W that it draws with a charging only cable or when I connect it to a host.

But when I connect it to a host it charges fine.

That does not make sense to me. I am a computer engineer. I would imagine that the hub should transfer power regardless of data being transferred. Clearly I am missing something though.

Does anyone know what is going on?

Thanks!

 

[FuzzyHarpyBug]

Honestly this just sounds like a bad idea all around. First of all, what sort of usb wall charger are you plugging the hub into? I guarantee you the amperage and voltage for all the devices you are trying to charge is not going to be the same, this is likely going to kill your battery life. Most USB hubs are controlled by a driver on your computer that will regulate the power to each device. They also use a certain amount of power themselves. Without the driver, the power output is likely to be erratic and potentially damaging.

As far as the cable difference, when not plugged into a wall charger the data cable will partially short itself causing a massive drop in efficiency, the unfortunate result of companies being unable to coordinate with each-other and conform any sort of standard.

 

[ratzlaff]

You have said some things that I have never heard before and find it hard to believe.

USB always supplies 5V. The power supply has a max current of 2A, but from my measurements it is less than that. I have not seen it vary whatsoever.

Where did you see that the driver controls the power? I have not heard that and would be thrilled to read up on that.

I would also be thrilled to read on how the data cable partially shorts. What pins are shorting? There are only 4 pins in usb (pre 3.0), Vcc, ground, and 2 data pins. How do they short?

I would love to read up on this. If you have any more links relating to this topic I would love them. I didn't see too much on wikipedia relating to this particular topic.

Also this hub is marketed as capable of recharging devices. QVS 13-Port USB 2.0 Hub UH2-13 - Micro Center

 

[carnageX]

You have said some things that I have never heard before and find it hard to believe.

USB always supplies 5V. The power supply has a max current of 2A, but from my measurements it is less than that. I have not seen it vary whatsoever.

Where did you see that the driver controls the power? I have not heard that and would be thrilled to read up on that.

I would also be thrilled to read on how the data cable partially shorts. What pins are shorting? There are only 4 pins in usb (pre 3.0), Vcc, ground, and 2 data pins. How do they short?

I would love to read up on this. If you have any more links relating to this topic I would love them. I didn't see too much on wikipedia relating to this particular topic.

Also this hub is marketed as capable of recharging devices. QVS 13-Port USB 2.0 Hub UH2-13 - Micro Center

I use a USB hub to charge around 4 devices. It's sitting by my bed, and my fiance and I both have our phones plugged into it at night, and occasionally our Nexus 7's. Haven't had an issue with any device in over a year. Albeit, it's slow charging... it's charging nonetheless.

As far as the pins shorting, this actually does happen. For phones for example, this is how they can tell if you're charging over USB or AC source. If the 2 data pins are shorted, that means it's charging over AC and your phone will usually pull more power (and charge faster). However, if the data pins are not shorted, the phone will think it's charging over USB and charge slower (not pull as much power).

This is why they make AC adapters for USB cables; the data pins inside the AC adapter are shorted out usually, and only provide VCC and ground. Whereas a standard USB hub will have all pins available and none shorted.

 

[petermarker]

As mentioned, the hub will simply not supply enough power (Amps) to actually charge multiple devices.

 

[carnageX]

As mentioned, the hub will simply not supply enough power (Amps) to actually charge multiple devices.

As my previous post stated, false. I've had 2 tablets and 2 phones plugged into a single hub just plugged into an outlet, and it's charged them. Granted its fairly slower, but it will indeed charge them.