[Galaxy S III Q&A, Help & Troubleshooting] revolvingsoul:
I'm looking to be able to use my external HDD (1TB WD passport) on my phone via OTG. As I understand, ntfs support varies with kernels etc but I'll cross that bridge when I come to it as I think there's a more fundamental problem.

I've got an OTG cable, and my mouse, usb pen drive, keyboard etc work with it. The HDD doesn't, because the phone can't provide enough power to operate the thing. I thought I could get around this by connecting it via my usb hub (which runs off external mains power) but when I connected this up to the phone and plugged the HDD in nothing happened. Likewise, the mouse and pen drive etc could also not be recognised by the phone when they were each plugged in via the hub (one at a time, I wasn't trying to run 8 things at once!) even though they worked perfectly when the phone itself was powering them when they were directly plugged into the OTG cable (if that makes any sense).

So, assuming it was a problem with the hub, I instead tried the method in this thread http://xdaforums.com/showthread.php?t=1828032 and made my own y type cable so that now rather than the phone providing power to the OTG peripheral, the power now comes from a standard USB phone charger. I'm fairly confident that I did all the soldering correctly and there weren't any short circuits.

When I tried using this, I had the same issue as with the hub. None of the mouse, the pen drive etc could be recognised with the modified OTG cable, which was odd as physically nothing had changed from the point of view of the peripheral plugged into the OTG (the data cables connecting it to the phone were unchanged, and it was still getting 5V power, just from the wall rather than my phone) which makes me think perhaps the problem is a software one where the phone only recognises a USB peripheral/begins USB host mode if the peripheral is actually draining power, since the power leads running from the phone side of the OTG cable are now just an open circuit.

Just to confirm I hadn't just snipped a data cable by accident when modifying the OTG cable, I re-soldered the OTG cable to how it originally was and it worked the same way it had previously. This means all the data cables are still intact, so I think it must be a software issue.

I thought maybe a way of testing this would be to modify the y cable and connect the red and black power cables coming out of the phone to each other via a fairly hefty resistor (so you still get power flowing from the phone even though the USB peripheral is powered by the wall). But it seems a bit dangerous!

Has anyone else had trouble with this? I've read around on forums and for a lot of people USB hubs and y type OTG cables seem to "just work", although I've not seen anyone with an i9300 reporting success. I'm running the latest version of liquidsmooth, but have also tested on CM10.1 and have the same problem. It might be an AOSP thing that stock samsung firmware will fix?

Let me know your experiences!

TLDR: I'm pretty sure I've got a software issue where my i9300 only recognises a USB peripheral/begins USB host mode via OTG if the peripheral is actually draining the phone's power, and so doesn't work when a USB hub or externally powered (y type) OTG cable is being used.

Thank you!