[emarkd]

So as many of you know, the factory USB option (6FL) is underpowered and won't properly spin many hard disks. BMW says it only supports ipods and flash drives, but I wanted to use something bigger. The solution that most people use is to purchase a USB power adapter to plug into the 12v socket in the armrest and power the drives using a y-cable. This doesn't work very well because the socket there doesn't power up until the car is started, but the iDrive powers up the USB cable before then, so your drive is not always seen. Plus the area under the armrest is quite small.

I decided to replace the power supply directly in the USB cable. It works great. I'm writing this so that others who feel comfortable trying this know that it can work, and maybe I can save you a little trial and error in the process. Notice that I'm not calling this a DIY. These are just a few notes to help someone who understands this procedure, not full instructions. Doing this incorrectly may fry your car's computer. If these instructions are not detailed enough for you, you probably shouldn't be attempting this.

1. All of the 6FL wiring can be accessed from the back of the center console. Removal instructions can be found in calvino's DIY for adding the rear power outlets. His car doesn't seem to have the 6FL option, but the wiring will be clearly mounted in the center just underneath the opening for the vents. The USB cable is the larger, 4-conductor DIN-style cable with a round connector in the center. You can unplug it safely to make it easier to work on. The driver's side goes up to the plug and is therefore out of the circuit if unplugged.

2. Inside, the cable has a layer of foil followed by a mesh shield, with the four conductors inside. Slit the cable lengthwise and fish out the orange wire, leaving the others inside the shielding. That's the +5V lead. You'll cut this wire and put your new circuit in series here.

3. Build your circuit. The one I used is attached below. It's actually very simple. The 5v lead from the car's USB cable is used to trip the coil of a relay. The relay acts as a switch that supplies power to turn on a 5v power converter. The power converter then supplies 5v down the USB cable to power the disk. I've left the power converter out of the schematic. Check google. They're simple to build or you can buy one pre-made. I used a Radio Shack 275-0232 reed relay and built everything on a piece of Radio Shack perfboard that I had laying around.

4. Install it. I put mine in a 270-1802 enclosure because it fits in the gap between the vents and the ashtray. You'll have to remove the retainer clip for the 6FL wires and leave them loose, but otherwise things fit fine. Wrap everything in some thin foam and you won't have any rattles.

That's it. I hope these notes are helpful to someone, but if you're uncomfortable trying this, don't. Not my fault if you burn something up.

[emarkd]

For those who are interested, here's a bit of an update:

My wife and I just returned from a car trip. I drove over 1500 miles in the past 9 days with my mod installed. The drive I carried was a 160 GB Maxtor OneTouch 4 Mini containing 21792 songs, totalling 107.5 GB. At first, the system still seemed to act up a bit. A few times on the first day of the trip, it jumped back to FM after starting back up, just like it used to before the mod. Maybe this is related to the indexing? Shortly though, the issues went away. For the rest of the trip, we only had one other anomalous issue. We got out for lunch one day and, after restarting the car, it started playing a completely different song than we were listening to before stopping. Pretty weird. Other than that, things worked great. We stopped many times for varying lengths of time and the playback restarted just where it left off. We also jumped around to the satellite and local FM stations and back to the drive and it all worked really well. This mod may not solve all of the issues with using a large disk drive, but it seems to help a lot.