Paralleling laptop USB power with external 5v supply.

Discussion in 'The Projects Forum' started by imbaine13, Oct 7, 2015.

  1. imbaine13

    Thread Starter Member

    Oct 6, 2013
    62
    0
    Hello everyone,

    Hope you're all enjoying yourselves. I on the other hand have hit a brick wall. I've got an external dvd drive that I usually burn dvd's with, connected to an old (1990's) model Toshiba laptop. I have recently realised it's supplying a little less power through the usb ports (its got 2) because about a month ago when I wrote a dvd, it really was struggling to get the job done, and a few days ago, there was so little power, it failed to complete a 3.8g.b write session.
    Today, when I tried burning another dvd, the computer shutdown power to all its ports which led me to reboot it to restore functionality, and confirmed my hunch.

    So, before doing anything foolish, I thought I'd first seek advice here.
    I've also got a 5v, 2A smps wall brick lying around which I'd very much love to put to use.

    Now to the question, what would happen if I connected the 5v power supply in parallel with the laptop's usb port (externally of course) to boost current to the drive ( as in diagram 3 below)?

    I'm I better off connecting the 5v brick directly to the external drive and the two green an white data lines from the drive to the computer through the usb, leaving the p.c's usb power lines untouched (as in diagram 1), or does the usb 5v supply from the computer need a load to determine which usb is active (as in diagram 2)? In the 2nd case, I could connect a 1.5 watt dummy load.

    The drive seems to struggle to keep up when watching dvd videos. It's of good quality and works well with other p.cs, which rules the drive out as the culprit.

    As always, I appreciate your time and help.
     
  2. pwdixon

    Member

    Oct 11, 2012
    488
    56
    I think you need a fourth option where similar to #1 but with the 0V connected straight through. There may be an issue with the driver software if it does not detect the drive power being taken but you should be able to identify that as a requirement if the system fails to work and a 'dummy' load may be required ala #2.
     
  3. ISB123

    Well-Known Member

    May 21, 2014
    1,239
    527
    If its supplying less current over time than its a problem with PSU/Battery.
     
  4. imbaine13

    Thread Starter Member

    Oct 6, 2013
    62
    0
    Thanks, pwdixon.
    I think I'll do just that. I mean, after serious thought, where could the harm possibly arise. As long as the p.c detects current being drawn from the port, and the drive doesn't care where the current comes from, then I guess both devices won't get confused, and/or will be happy.

    So thanks again, very helpful.

    And ISB123, yeah. I agree with you, the power supply seems to be getting a little tired. But right now, I'd rather perform a simple fix coz I'm losing storage space by the hour and need to transfer stuff over to dvd's asap.
    Thanks as well.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,090
    3,027
    I agree with pwdixon about sharing the same ground all around. I wouldn't bother with a dummy load unless it doesn't work without it. I bet it will but that's just a hunch.
     
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