3

Ok, Recently I have purchased this USB Y cable from Amazon.

Storite USB 2.0 Type A Male to Dual USB A Male Y Splitter Cable Cord Black -50cm

y-cable

I purchased it so I can use it with external hard disk to my 10 year old PC which wasn't able to provide enough USB power to the disk. After getting the cable, I connected it to PC and found it didn't provide enough USB power still.

Then I tried to check the cable with laptop. This laptop is a newer one and one USB port is always enough to run the disk as always (Generally I use USB male to male cable type A to connect this disk to laptop and it works fine).

So, to check the cable..

  1. First, I connected two male plug ends to laptop and third male plug to disk, it works fine.
  2. Second, I connected one usb plug to laptop (the one continuous with thick cable in pic) and other end to disk and it runs fine.
  3. Third, I connected the alternate usb plug to laptop (the one with thin wire in pic) and other end to disk, and now neither the disk rotates nor usb is detected, but disk shows led on which means power connection is active I guess..

From the second test, it is clear that the two male plugs (attached with thick cable in pic) carry both power supply and usb data. Whereas from the third test, it shows the male plug attached to thin cable doesn't carry enough power or usb data, or atleast this part of my cable is damaged I guess..

  • So, I would like to know how are they designed?
  • Are all the three plugs meant to be connected to USB power and data?
  • Is there any way to check if the Y-cable is faulty? I only wanted to check if that cable is faulty so I can replace it if it is..
7
  • Should add: In addition to the power from each port being a factor, the length of internal cable inside the PC can also be a factor if you are using a frontal USB port - try one directly on the motherboard. The issue with long(er) cables is resistance, causing voltage drop. Also, some computers run multiple USB ports through a single power limiter/fuse, meaning two adjacent ports together may not provide 2x the power of one port.
    – qasdfdsaq
    Aug 20, 2015 at 14:39
  • I connected it directly to the motherboard usb sockets.. GIGABYTE G31M-S2C .Not sure if it has single fuse.
    – Bharat G
    Aug 20, 2015 at 14:46
  • usb 1.1 does not have enough milliamps even using 2 ports for power, are they usb 2.0 ports?
    – Moab
    Aug 20, 2015 at 14:57
  • They are usb 2.0 ports. Other usb 2.0 peripherals work fine at usb 2.0 speeds..
    – Bharat G
    Aug 20, 2015 at 15:03
  • @qasdfdsaq "the length of internal cable inside the PC can also be a factor if you are using a frontal USB port" really? USB 2.0 is designed to work up to 5m. Can a few cm inside the case make that much difference?
    – DavidPostill
    Aug 20, 2015 at 15:13

2 Answers 2

6

How is a USB-Y cable designed?

It is designed for devices which require more power than is available from a single USB port.

Whereas from the third test, it shows the male plug attached to thin cable doesn't carry enough power or usb data

This extra connector does not have any data lines (D-, D+); it only has the power lines (GND, VBUS).


Are all the three plugs meant to be connected to USB power and data?

Yes. The two connectors on the Y end should be connected to the PC/Laptop and the other end to your USB device.


I want to check if the cable is faulty.

First, I connected two male plug ends to laptop and third male plug to disk, it works fine.

  • That is how the cable should be used so it is not faulty

  • The other tests are using the cable in a way it is not meant to be used so the tests are meaningless.


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)


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

4
  • Do U think Male plug alone attached to thin cable should have rotated the disk when connected to laptop or external usb charger that provides adequate power. It should have rotated the disk I guess even if it doesn't has Data bus D+ D-. What do u think??
    – Bharat G
    Aug 20, 2015 at 14:49
  • @BharatG See my answer "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. "
    – DavidPostill
    Aug 20, 2015 at 14:51
  • Ok. So there is no way to check if the cable is faulty. I only wanted to know if the cable is faulty, so i can replace it if it is..
    – Bharat G
    Aug 20, 2015 at 15:04
  • 1
    @BharatG You said "First, I connected two male plug ends to laptop and third male plug to disk, it works fine." - that is how the cable should be used so it is not faulty. The other tests are using the cable in a way it is not meant to be used so the tests are meaningless. Answer updated.
    – DavidPostill
    Aug 20, 2015 at 15:06
0

Just by looking at the cable I can see that it is faulty. I violates nearly every USB spec written. To verify the cable safe take a wire cutter and cut each USB-A plug from the cable or cables it is attached to. This assures that it cannot damage another computer. After this point the pieces should be tossed into a refuse bin.

Whatever device was using this cable needs to be replaced as well, that had violated the USB spec too. Perhaps with enough time with a soldering iron it could be repaired but it's difficult to say if that is possible or worth the time. It may be best to toss it in the bin too.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .