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3 years ago I went volunteering and brought back this weird USB cable and in those 3 years i never could figure out how to use this USB cable and what is the purpose of its disposition. So... what do you use this cable for (I think those are 3 USB 2.0 connectors - I don't know how to differenciate USB 2.0 and older USB's...) ?

enter image description here

Amine Kchouk
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  • USB cables hadn't changed between USB 1.0 and USB 2.0. It's only USB 3.0 that uses different cable. – gronostaj Jul 04 '15 at 19:47
  • Type-A plugs and receptacles from both USB 3.0 and USB 2.0 are designed to interoperate. Type-B plugs and receptacles in USB 3.0 are somewhat larger than those in USB 2.0; thus, USB 2.0 type-B plugs can fit into USB 3.0 type-B receptacles, while the opposite is not possible. – DavidPostill Jul 04 '15 at 20:08

2 Answers2

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What is this weird USB cable

The cable is called a USB Y-Cable. It is designed for devices which require more power than is available from a single USB port.

What are the 2 different kinds of Y-Cable?

  • One male connector, two female connectors

    There are two types of the one male two female cables. One is a basic charging cable, splitting one port's power across two devices. The other is a specialised cable that somehow splits the data lines - and it's only used in very specific applications.

  • Two male connectors, one male or one female connector

    What happens is you have your USB cable, one side for the host and one for the device, but with an extra connector attached. This extra connector does not have any data lines (D-, D+); it only has the power lines (GND, VBUS). It's attached in parallel to the existing cable. In other words, VBUS is connected to VBUS and GND is connected to GND.

Source Can I safely connect the power-only-end of a USB-Y cable to an other power source? answer by Bob)

So what is this weird Y-Cable?

enter image description here

The extra power plug is sometimes a double-sided plug, with both male and female.

It's a pass-through so that extra port used isn't totally wasted.

The female connector on the back of the plug allows a low-current device to use the second port.

Power requirements

Some devices, such as high-speed external disk drives, require more than 500 mA of current[89] and therefore may have power issues if powered from just one USB 2.0 port: erratic function, failure to function, or overloading/damaging the port.

Such devices may come with an external power source or a Y-shaped cable that has two USB connectors (one for power and data, the other for power only) to plug into a computer. With such a cable, a device can draw power from two USB ports simultaneously. However, USB compliance specification states that "use of a 'Y' cable (a cable with two A-plugs) is prohibited on any USB peripheral", meaning that "if a USB peripheral requires more power than allowed by the USB specification to which it is designed, then it must be self-powered."

Source USB

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DavidPostill
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    This one looks like it has 3 male connectors. – gronostaj Jul 04 '15 at 20:00
  • Yes, the 2nd kind is two male at one end and either a male or a female at the other - that is represented by (fe)male. I will clarify the answer. – DavidPostill Jul 04 '15 at 20:03
  • Just to complicate things, the extra power plug is sometimes a double-sided plug, male and female. It's a pass-thru so the extra port isn't totally wasted. The female connector on the back of the plug allows a low-current device to use the second port. – fixer1234 Jul 09 '15 at 23:17
  • http://i.imgur.com/qMzQD8p.jpg – fixer1234 Jul 10 '15 at 00:33
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The cable is meant for USB powered devices that require more current than 1 USB connector can provide. I have that cable for my CD Writer.

The single connector at the end is connected to the device and the other 2 connectors are connected to the computer. I believe that the data is only provided at one of the connectors, but power is needed from both.

LDC3
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  • Which is/are the input(s) and which is/are the output(s) ? – Amine Kchouk Jul 04 '15 at 19:24
  • -1 USB-A is clearly not meant to be plugged into a device. – kinokijuf Jul 04 '15 at 19:26
  • @kinokijuf I have the exact same cable in front of me and they are clearly USB-A male connectors. Not all manufacturers follow the rules. – LDC3 Jul 04 '15 at 19:29
  • Well, the only thing the cable can be used for is shorting two USB sockets together. Not recommended. – kinokijuf Jul 04 '15 at 19:44
  • @kinokijuf Not true (see my answer) - the connectors that are intended for the USB sockets on the computer **are wired differently**. – DavidPostill Jul 04 '15 at 19:52
  • @AmineKchouk USB doesn't really have input/output. In the case of this cable one Y connector is 2 way (data) and the other end of the cable is 2 way (data) as well as one wat input (power). The other Y connecter is one way output (power) – DavidPostill Jul 04 '15 at 20:07
  • @DavidPostill Well, but the **other** end can’t be plugged in to anything **but** a computer. – kinokijuf Jul 04 '15 at 20:10
  • @kinokijuf As we cannot see from the photo whether the ends are male or female we cannot tell. – DavidPostill Jul 04 '15 at 20:18
  • @kinokijuf The 2 connectors that are close together go into the computer, after all the computer supplies the power. Inside the device, the power can be split between the connector and the internal circuitry so not all the power goes into the USB power connectors. – LDC3 Jul 04 '15 at 20:40
  • @LDC3 And the far connector goes where? Devices have B sockets, not A's. – kinokijuf Jul 04 '15 at 20:46
  • @kinokijuf "USB 2.0 Type A Male to Dual USB A Male Y Splitter Cable Cord Black For HDD Case" - These cables are **specifically** sold for portable HDDs. – DavidPostill Jul 04 '15 at 21:15
  • @kinokijuf If you need extra power for a device, what better way to ensure they use the correct cable than one that is not very common. Likely, if you use the common USB-A to USB-B cable, which doesn't supply enough power, the device operates incorrectly and you have thousands of complaints, and maybe your product doesn't sell from the bad reputation. If you force the connection to use the correct cable, then the lack of power to the device is avoided. Devices that have their own power cord can use the regular cable. – LDC3 Jul 04 '15 at 21:54
  • Then don’t use a standard jack. **This cable can burn out USB ports on motherboards.** – kinokijuf Jul 05 '15 at 05:54
  • @kinokijuf It might, but it is the only way to power your device. – LDC3 Jul 05 '15 at 05:59
  • @LDC3 Devices **don’t have A-ports**. – kinokijuf Jul 05 '15 at 06:30
  • @kinokijuf You mean devices that don't need extra power don't have A-ports. Have you seen every device made that needs extra power to make that claim? – LDC3 Jul 05 '15 at 14:25
  • @LDC3 No, i mean that **A-ports are on hosts, B-ports are on devices**. USB is **asymmetrical**. – kinokijuf Jul 05 '15 at 21:18
  • @kinokijuf Obviously not if there is a need for this cable. And like I asked, have you seen **every** device that needs extra power with only B-ports? – LDC3 Jul 05 '15 at 22:07
  • @kinokijuf I have a USB hub that uses an A-A plug cable. Does that count as a device? – jiggunjer Jan 07 '16 at 01:46