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  • September 22, 2011 at 6:47 am #2207426

    Why is there an extra USB connector on USB connection cable?

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    by gaurav003 · about 13 years, 6 months ago

    I have a transcend optical drive that i use for reading and writing DVDs with my laptop. The connection cable is a USB type A-B cable. However, at the Type A end there is an extra provision for another Type A connection with a very short length of cable (about 20 cm). what is this third connector for?

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    • September 22, 2011 at 6:47 am #2895892

      Clarifications

      by gaurav003 · about 13 years, 6 months ago

      In reply to Why is there an extra USB connector on USB connection cable?

      Clarifications

    • September 22, 2011 at 7:51 am #2895884

      USB Connector

      by avlwiz · about 13 years, 6 months ago

      In reply to Why is there an extra USB connector on USB connection cable?

      According to the manual the second USB connector provides additional power for the
      CD/DVD Writer. Please make sure to connect both USB connectors to your computer???s USB ports.

    • September 22, 2011 at 8:11 am #2895882

      The second cable is unnecessary here…

      by dldorrance · about 13 years, 6 months ago

      In reply to Why is there an extra USB connector on USB connection cable?

      Mine works just fine with the longer cable only plugged in. A second (extra power) cable might be necessary with a 3.5 inch HDD, whose motor requires more current.

    • September 22, 2011 at 8:39 am #2895879

      its for additional power

      by markp24 · about 13 years, 6 months ago

      In reply to Why is there an extra USB connector on USB connection cable?

      Hi
      when running/powering (with out an external ac adapter) the CD drive (or any device) from the usb (usually 1.1 will need the second usb connection)
      the usb will provide power. The usb y cable is to use one port for a data/power connection and one port solely for power with a bus powered USB drive. Many laptop USB ports are not “powered”, they may provide insufficient voltage for the USB bus powered drive. This allows you to draw power from two ports and generally this will be enough for both.

    • September 22, 2011 at 9:50 am #2895862

      plug both in, and use it anyway . . .

      by who am i really · about 13 years, 6 months ago

      In reply to Why is there an extra USB connector on USB connection cable?

      when reading a disc the power draw isn’t that much and it may function just fine on the single plug,

      but if you go ahead and try to write a full CD or DVD
      you’ll find that the extra power connector is required
      writing requires anywhere from 1/3 to 2x more power than reading does
      and the burn will likely fail to complete if the secondary power plug is not used

      .

    • September 22, 2011 at 9:53 am #2895860

      Not more power, more current :)

      by robo_dev · about 13 years, 6 months ago

      In reply to Why is there an extra USB connector on USB connection cable?

      It’s all 5Volts,just double the current. The standard limit is 500 mA per USB port, while some old hard drives need more juice than that.

      Note that hardware damage can result if you plug a high-current device into a standard port. While USB is supposed to detect over-current, and not supply power, I’ve seen some USB adapters make an acrid burning smell followed by them no longer working.

    • September 22, 2011 at 1:48 pm #2895823

      It never hurts to provide a teachable moment

      by robo_dev · about 13 years, 6 months ago

      In reply to Why is there an extra USB connector on USB connection cable?

      In my opinion, more people need to understand the basics of electricity, such that connecting two 5V 500 mA USB connectors in parallel does not give you 10 volts, it gives you 5 volts at 1 Amp (5 watts).

      In theory a 12 volt power supply could supply the same amount of power (5Watts), but the higher voltage would most likely burn out the interface and destroy any attached peripheral.

    • September 22, 2011 at 2:53 pm #2895818

      Also something that has not been mentioned here

      by oh smeg · about 13 years, 6 months ago

      In reply to Why is there an extra USB connector on USB connection cable?

      The second USB Plug is often only a Power Plug it has no Data Connections inside it.

      if you look at the actual Cable you’ll see that the Second USB Plug has a thiner cable it only has the leads for the extra Power. 😉

      So if you where to plug in that plug the drive would spin up but not actually appear on the Monitor.

      Also if you look at the specs of your computer you may very well find that it doesn’t actually provide 500 Milliamperes at the USB Sockets. Modern NB’s have reduced the Available Current at the USB Ports to prolong Battery Life. So while it may not apply to your current computer it could very well apply to any other computer that you plug the drive into. Of course if you where to use a Powered USB Hub things would be different but even then I wouldn’t be trusting what should be happening as what actually happens is quite often different. 😀

      Col

    • September 23, 2011 at 7:38 am #2899942

      Go to the source – the USB specification

      by realvdude · about 13 years, 6 months ago

      In reply to Why is there an extra USB connector on USB connection cable?

      http://en.wikipedia.org/wiki/USB#Power

      Many responses have partial right answers. One thing to keep in mind about USB power, is that there is a process between the requesting (device) and supply (host) side of things. Therefore and high current device will not draw more than can be supplied and conversly the device will know if not enough power can be supplied. That is supposed to keep both devices safe.

      Now for that second connector, and other devices that may cause problems:
      http://en.wikipedia.org/wiki/USB#Non-standard_devices

      If you want something more confusing, check out Power Over Ethernet.

    • September 23, 2011 at 8:13 am #2899932

      Power defined

      by ciarocci · about 13 years, 6 months ago

      In reply to Why is there an extra USB connector on USB connection cable?

      The manuals, and the person who said the plug provides more power are right. The way it does this is by increasing amperage. P=I*V (power equals amperage times voltage). So, if I increase either voltage OR amperage, I am increasing power. Saying “Not more power, more current” is an incorrect statement, as supplying more current IS supplying more power, as well as supplying more voltage IS supplying more power. Increasing either one will give you more power.

      Please refer to the wikipedia link about power. It explains this in detail.

      http://en.wikipedia.org/wiki/Power_(physics)

    • September 23, 2011 at 5:27 pm #2899894

      extra usb plug

      by rmixon1 · about 13 years, 6 months ago

      In reply to Why is there an extra USB connector on USB connection cable?

      R.T.F.M.

      • June 29, 2013 at 7:27 pm #2432164

        Reponse To Answer

        by chas55 · about 11 years, 9 months ago

        In reply to extra usb plug

        That’s fine if the device came with a F.M. 🙂

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