How to tell charge-only USB cables from USB data cables

usb

Like most computer hobbyists and programmers, I've amassed boxes of USB cables to connect USB, Micro-USB, and Mini-USB to chargers, computers, and gadgets. These cables are a mix of phone charger cables, and cables that came with external hard drives, bike lights, GPS units, and other miscellaneous gadgets. The problem is, they all look the same, just plain black cables.

How can I tell if one of these cables is a charge-only USB cable instead of a USB data cable? Ideally, I would love to rely on some visual clue, but I have a multimeter I could use to test the cables with if I knew a good approach to this.

My goal is to label these cables so I can resolve this ambiguity so when I reach in to my box of cables, I know which cable to use for charging my phone and which one to use to synchronise my GPS with my computer.

Best Answer

The kind of cable you mean is missing the D+ and D- data lines. It simply doesn't have those wires inside the cable.

You can test for continuity or resistance using a multimeter. Probe between the corresponding data pins: D+ on one side to D+ on the other, or D- to D-. The D+/D- lines are the middle two pins of a USB connector. Just select one on one side of the cable, and test continuity to both of the middle pins on the other side.

You will see no continuity or a high/"infinite" resistance on your meter if the cable is missing data wires and is a "charge only cable".

Technically USB requires the data lines to request more power from a host device, so a cable missing these connections would, in theory, only let devices charge very slowly. In practice most USB hosts will not enforce such a limit. It is also possible that some phones will refuse to charge without data lines in the cable.