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This is a nice little helper for everyone trying to use an express card usb3 controller with bus powered harddisks.

As sometimes the express card slot does not provide enough juice to run bus powered devices, and the solution provided by the manufacturer requieres an external supply from mains would prevent mobile use, I came up with this cable to add some extra energy from one of the regular usb ports.

From experience I knew that the built in usb ports of my laptop are capable of running harddisks and external dvd/blueray drives. To prevent overload on the usb port in the moment of drive spinup, I added a capacitor next to the plug which goes into the usb3 express card.

You would need a plug fitting the power input of the USB3 Express card.
Furthermore a USB Plug and some Cable, or you cut a USB cord and use half of it. Wikipedia has the pinout, or measure if you can.
Last but not least a capacitor which can handle the 5 volts, i used a 100uF which was literally lying around on my desk.

Please note that the capacitor is sensitive about polarity. You might want to plug the cable into a USB power supply first, instead of potentially frying your computers USB port.

The plug polarity is also an issue when the manufacturer does not provide this information somewhere on the card. Usually the pin is hot, but you should measure to make sure there is something positive coming from the pin (might be less then 5v due to a diode inside) and that the outer contact is GND.

This would be the advised order in which to connect your hardware:

1. Install USB3 Express Card. Your computer should indicate once the card was initialized and the driver loaded.
2. Connect the cable to the USB port of your laptop. This allows the capacitor to charge before being connected to the load.
3. Plug the cable into the USB3 express card.
4. Connect the Harddisk to the USB3 card.
5. Enjoy!

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