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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.

Peter Mortensen
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Benzo
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    I'm sure there might be exceptions, but I was under the impression that they are both the same. The data pins must be shorted to signal a higher amp draw, but I'd imagine this would be done on the charger end, not in the cable. – Jarrod Christman Nov 25 '14 at 20:34
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    @JarrodChristman - In my experience I've had cables that simply wont carry any data, but still charge the device (these have all been from phone chargers with removable cables, but they get mixed up, as they look exactly the same.) – UpTheCreek Jan 22 '16 at 14:10
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    Simply connecting a USB device you know is working is the fastest and most accurate test there is. – Dmitry Grigoryev Jun 23 '17 at 07:57
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    I'd throw out all the "charge-only" cables. As the other answers have indicated, charging over a cable with the data lines disconnected is slow at best, and overloads the port at worst. If you want to inhibit data communication, use a [USB condom](https://shop.syncstop.com/products/usb-condom) or one of its many clones that reproduce the power negotiation while blocking data. – Simon Richter Apr 09 '18 at 20:17
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    Charge-only cables are still useful (to me, anyway)! It's a shame there seems to be little quality control or regulation and one can end up with lots of charge-only cables, but they are useful to have around anyway. I tie two knots in a cable if I find it is charge-only, and three knots if it doesn't work at all then throw it in a box I keep for electrical junk that I intend to dispose of properly at a later date. – drkvogel Feb 16 '21 at 11:09

8 Answers8

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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.

tehwalris
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    You're latter comments about the dataline being required to request more power could explain why the 1.2A USB power supply I have for my raspberry pi, when plugged into a mobile, displays an error saying that it is unable to charge quickly and indeed takes a long time to charge. – flungo Nov 25 '14 at 20:59
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    It's probably going to be easier to try the cable on a device than it will be to probe the pins of a micro usb plug with a continuity tester. Once you have figured out which is which you can mark the limited ones with colored tape or heatshrink or a wire tie zipped tight or whatever. – Chris Stratton Jul 03 '15 at 19:34
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    The last paragraph is actually a bit misleading. The USB battery charging standard defines two types of ports: Charging ports, and "regular" data ports (and combi ports). A charging port is one that supplies >500mA@5V, but can't do data. A charging port is indicated to the device by a short between the D+/D- lines. QC aside, there's no digital data communication. The short *should* be implemented in the charger, but *some* charge-only cables and adapters actually short these in the MicroUSB plug or cable itself, which leads to the sorts of shenanigans like the USB-C cables blowing up laptops – RegularGDPR Sep 18 '16 at 14:51
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Look for something on cable like: (some number)AWG/1P. If it does exist then you have shielded twisted pair of conductor denoted by P above. And they use for data transmission.

Here: (some number)AWG/1Pdenotes

  • some number = number of wire gauge
  • AWG = American Wire Gauge?
  • 1 = Number of pairs
  • P = shielded twisted pair of conductor

28AWG/1P (for data) +28AWG/2C (for charging)

Junaid
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You can tell that a cable almost certainly has all four wires connected and will reliably transfer USB data at the speed it's rated for if it is unmodified and has the USB trident logo on top of the plugs:

USB Trident Logo alt text (Images from Wikipeida.)

The USB standard does not provide for cables without data lines, and the USB Implementors Forum does not allow the use of their trademarked logo above on non-standard cables.

(And yes, to address the comments, trademark law is not always perfectly enforced. But nor is it particularly poorly enforced in most first-world countries even for low-value products such as soft-drinks and USB cables. Further, simple testing of connectivity with a multimeter is no guarantee that the cables do not have other issues related to their inductance and capacitance that will cause problems with data transfer.)

cjs
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  • Just because something is not allowed does not mean it does not happen – Chris Stratton Feb 17 '20 at 00:40
  • @Chris Trademark violation is rare in most countries because trademark owners have legal means to enforce their trademarks, including products barred from import or seized if the manufacturer is not local. When you buy a can of what is clearly labled "Coca-cola" it's almost certainly not Pepsi or some other drink instead; the same is true of USB cables with the logo. – cjs Feb 17 '20 at 01:15
  • Not in practice, no. Cheap products like random cables fly under the radar much more readily than fake soft drinks. You really can't rely on the pattern on the plastic - the other answers on this page propose *technical* methods of verification which in contrast are reliable. – Chris Stratton Feb 17 '20 at 05:02
  • @ChrisStratton Presumably one might reasonably assume that a cable without the symbol is a charge-only cable (and if it happens to be a data cable, that's an unexpected bonus). – Andrew Leach Oct 27 '20 at 10:39
  • @AndrewLeach, no its as likely that one without a symbol simply didn't want to pay to use that – Chris Stratton Oct 27 '20 at 12:31
  • @ChrisStratton While the technical tests proposed are indeed more reliable, you should not ignore that different kinds of tests (using a multimeter, looking at the cable) have different costs. If you're in a hurry, need to grab one cable from a box of them, and don't have a continuity tester handy, it's better to have this test than none at all. – cjs Oct 31 '20 at 07:07
  • Nonsense, use your computer, that molding means nothing! It may have been fake from the start, and even an actual four wire cable is of no use if it no longer works. – Chris Stratton Oct 31 '20 at 11:57
  • @ChrisStratton I am unclear as to whether you are saying that a random choice between a marked and unmarked cable is as likely to produce a charge-only cable as using the one without the USB symbol, or that everybody is always in a situation where testing a cable with a device and computer is always as convenient as simply grabbing a cable from a number of them, or both. Regardless, I disupute both propositions. If you want to scale back to "this test is not as reliable as other tests, but can be faster" we would be in agreement. – cjs Nov 01 '20 at 06:54
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If the cable has any markings on it, look for the wire size and amount on it. They will typically say AWG 22-2 or similar for a 2 conductor of AWG size 22 cable. A 4 conductor cable would be different.

Of course, you could find a cable that has four conductors inside but not all four wires connected, so it would still be a charge only cable. But that seems like a waste of copper.

Passerby
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    This is a good answer. Many times the wire gauge will be different for the power conductors and the data conductors. See this image: http://www.usb-cable.com/mini-b-usb-cable-short-8-inch.jpg . If you look at the writing on the A end, you'll see "28AWG/2C + 24AWG/2C". I believe this stands for 2 28AWG conductors and 2 24AWG conductors. This would suggest it has all four conductors, meaning it can be used for charging and for data. – DerStrom8 May 27 '16 at 17:59
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You'd like an easy way to tell a "charging only" cable from a complete cable. Unfortunately, your only solution is to place your own sticker or wire tie around the cables.

The USB Implementers Forum does not recognize charging only cables, and does not publish any form of graphic or symbol to distinguish one from the other. To contact the USB-IF on this issue see http://www.usb.org/about .

The production process for a "charge only" cable is simply to leave out the two center wires. There's no enforcement of any rules related to USB, so you just get whatever the factory churns out.

To see what you've got plug in a phone to a PC and browse files. If browsing works, you have 4 wires. If not, chances are you've got just 2 wires.

Note that the center two wires are used even for charging. There's a bizzare and incompatible set of signals used by the device to determine how much current (charging power) to try and draw. Without the center two wires, you get whatever the device's default behavior is (which may be slow charging).

Bryce
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  • " Without the center two wires, you get whatever the device's default behavior is (which may be slow charging). " It should be slow charging, if the device's behavior meets the USB spec. The practice of USB devices slow charging if the data contacts are left floating goes way back, the USB-BC spec codified this as specified behavior later. This was to allow for the construction of inexpensive 5 watt USB chargers. It was inevitable, and likely predicted, that someone would exploit this standard to make cheap USB charging cables. – MacGuffin Feb 16 '21 at 12:02
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Use a Smartphone, if it gives the message "Connected as a media device" the cable allows data connection, if not, the cable is a charge-only cable!

Rui Monteiro
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The outer insulation on charge only cables tends to be thinner than that of a data/charge cable because they physically contain 2 less wires. but the continuity test described above is the only way to be 100% certain.

scott
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Not sure my experience is true generally, but when I look at the end of a charge-only cable, I see an "arrow" symbol, while USB symbol for a data cable.

Pls see my blog post for details.

hiroto
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    Link-only answers is frowned upon. Please add the relevant parts of the blog post to your answer. Your post would become useless if the blog post gets deleted in the future. – try-catch-finally Apr 08 '17 at 08:23