Apple sells two camera adapters for the iPad, one with a USB port on the end and one with an SD card slot. For 30 pin iPads these two come as a package deal, while the new Lightning connector iPads require the more expensive versions, sold individually. These adapters used to be really useful, but a couple of years ago Apple put a software restriction in place, limiting the power output of the adapters from 100mA to 20mA.
Ever since then, most USB flash drives connected to the USB version of the adapter have just prompted a “Cannot Use Device: The connected USB device requires too much power.” You can always use a powered USB hub, but adding AC power dependency to the package isn’t ideal. That has rendered the USB adapter much less useful than it used to be, and I didn’t even bother buying one when I switched to the Lightning-equipped iPad mini. That changed a couple of days ago, when a thread on MacRumors alerted me to a trick that YouTube user withapacketofsweets discovered. Turns out, connecting an unpowered hub between the flash drive and the adapter somehow makes the whole power issue disappear.
After hearing about this trick, I ran out and bought a Lightning to USB Camera Adapter and a cheap unpowered hub. Sure enough, the drives that triggered the power warning with just the adapter, work perfectly when connected via the hub. I can even connect several drives at once, and it still works. Drives light up, and can be accessed just fine. If your device is jailbroken, you can load up iFile, and access the full file system on the drives, including all files. This means you can transfer documents to or from the drive, play video or audio straight from it, and so on. Each drive shows up in the sidebar in iFile, and everything’s just dandy. If your device is not jailbroken, however, you’re stuck only accessing photos and videos.
Since this uses unpowered hubs, which don’t add any power to the equation, it seems a bit illogical that it should work, but I think it has to do with the 20mA limit being a software limitation. I’m guessing the iPad supports hubs natively, and actually grants 20mA of power to each resulting USB port on the hub. It then delivers the total amount of power this comes out to (80mA on a 4 port hub, for instance) to the hub, allowing the hub to grant more than 20mA per port. This is just a theory, but at least it explains why this trick works.
The lack of proper USB drive support has been a major complaint about the iPad for years, especially from educators and other people who need to be able to connect a USB drive. With this trick and an available jailbreak for all iPads right now, that problem is solved for anyone who actually wants to solve it, which I think is great.