It is frustrating to have older hardware just sitting around collecting dust or getting in the way, so if it can be repurposed and made useful once again, then it is a cause for joy. Today’s SuperUser Q&A post discusses the possibilities of repurposing an old USB 1.1 hub device for a curious reader.
Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.
Photo courtesy of Alexandros Kostalas (Flickr).
The Question
SuperUser reader user1049697 wants to know if it is possible to use an old USB 1.1 hub to charge his devices:
Is it possible to use an old USB 1.1 hub to charge devices?
The image below shows a hub similar to the USB 1.1 hub I have:
(Update) I did try this with some devices and the results are as follows:
My old Android 2. 3 device will charge, albeit very slowly. My iPhone 5S will not charge at all.
The Answer
SuperUser contributor Bob has the answer for us:
Have something to add to the explanation? Sound off in the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.
The vast majority of simple hubs do not really implement any sort of power control. They will just connect the USB power lines directly to either their host or an external (regulated) power supply, which means you would effectively be sharing the capacity of the power source over all ports.
In practice, however, USB charging gets quite complex. The bottom line is that your USB 1.1 hub will probably charge your peripherals, but at a reduced rate. This is not because the hub is actively limiting the current output, but because peripherals will limit the current they draw unless they can positively confirm the host is capable of supplying that current (to prevent damage to hosts that cannot).
This reduced rate depends on the specific peripheral and the specific hub, but it likely ranges from 100 mA to 500 mA, which is far less than a modern smart phone’s maximum (over 1,000 mA).
To elaborate:
If the host implements some kind of power control, then the peripheral must initiate a data connection and negotiate properly. Even though this is technically required by the specs (except the newer battery charging specs), some peripherals might not do so. I imagine most smart phones will at least try, but there are many ‘dumb’ USB peripherals that will not.
In the case of a hub connected to a USB power supply without a proper host, it might not work at all.
Negotiation is as follows:
Each peripheral is permitted to draw one unit load without negotiation. Each peripheral should communicate with the host to request more units. USB 1. 1 and 2. 0 define one unit load as 100 mA, with a maximum of 5 unit loads (500 mA). USB 3. 0 defines one unit load as 150 mA, with a maximum of 6 unit loads (900 mA).
Modern devices often need more power (smart phones often draw 1,000 mA – 2,000 mA).
There is a battery charging specification that deals with this. Read through the article “How USB Charges Just About Any Electronic Device” for details on how its negotiation and detection works, but that is not too important.
The charging limit is 1,500 mA, but only if the data lines are shorted together (or respond as if they have been). This is not the case with a data-capable host like a USB hub. There is an additional profile that deals with this, but a USB 1. 1 hub probably does not implement it. With a non-compatible host, most smarter peripherals will fail to detect a high-capacity source and will therefore fall back to charging at 500 mA at most. This means your USB hub will likely charge the device at a significantly slower rate than plugging the peripheral directly into the charger.
There are some other specs such as Apple’s protocol, Qualcomm’s quick charge protocol, etc. They all have their own detection and negotiation methods. They will also not work with a USB 1.1 hub.
There is a newer USB Power Delivery spec, but almost nothing implements it yet and it deals with all sorts of wacky things like different voltages.
