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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
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..
- First, I connected two male plug ends to laptop and third male plug to disk, it works fine.
- 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.
- 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..
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 – 2015-08-20T14:39:30.440
I connected it directly to the motherboard usb sockets.. GIGABYTE G31M-S2C .Not sure if it has single fuse. – Bharat G – 2015-08-20T14:46:16.637
usb 1.1 does not have enough milliamps even using 2 ports for power, are they usb 2.0 ports? – Moab – 2015-08-20T14:57:56.707
They are usb 2.0 ports. Other usb 2.0 peripherals work fine at usb 2.0 speeds.. – Bharat G – 2015-08-20T15:03:11.950
@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 – 2015-08-20T15:13:52.500
@DavidPostill: For power delivery, yes. Even a 2m cable can reduce available power delivery down to less than 100mA, obviously depending on quality of cable. Not to mention I've personally come across dozens of cases where frontal ports don't supply sufficient power. Some empirical tests here: http://www.yoctopuce.com/EN/article/usb-cables-size-matters
– qasdfdsaq – 2015-08-20T15:22:05.163