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Thread: wierd, slim dvd -> USB adaper MUST use ps/2 port for power...

  1. #1
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    wierd, slim dvd -> USB adaper MUST use ps/2 port for power...

    I have a slim slot loading DVD Rom drive (working pull from an iMac)

    I got an ebay enclosure that takes the drive to USB. the description said "powered off USB port" "no external power needed" etc. yet, it came with an adapter that plugs into your keyboard port "just in case"...

    I tried it out. It would ONLY work if I use the ps/2 port adapter to get more power. so I got a 3-headed USB cable (2 ends go to the computer, 1 end goes to the drive ... this lets you pull power from 2 USB ports for more power, get it?)

    still no dice. I don't know what gives. each USB port gives 500ma of power right? 2 usb ports would give you 1 amp, and i KNOW this drive doesn't pull over an amp....

    how much power does the ps/2 port give? this is stupid, I don't' want to have to run another cable if it's not needed.... just a pet peeve i guess. any ideas?

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    2 usb ports would give you 1 amp, and i KNOW this drive doesn't pull over an amp....
    Not necessarily 1 amp, both draw from the same source. You might try getting a powered hub and having the drive plugged into that (of course keeping the hub close to the system). If you're confortable with wiring electronics, you could could tap 5V off your system's power supply and running it down the USB cable (make sure you use diodes to prevent damage to the USB ports).

  3. #3
    Variable Bitrate drait's Avatar
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    Don't be so sure the drive doesn't draw over an amp at full speed. A lot of the slim drives have lower power requirements when idling or at half-speed. But when they need to spin up or do heavy disc access, they can draw some serious juice.

    If the enclosure you have there is similar to the one that Centrix sells, then it's most likely the same problem a lot of people have with those drives; even with both USB connections and PS/2, you're still not providing the max 2-3A for the drive at high speed. It's probably why the cables are so short too; extending it even further than the few inches they give you would probably increase the likelihood of even more problems.

    If a powered USB hub doesn't resolve the issue, try providing 5V to the drive from one of the molex connectors on your PSU.

  4. #4
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    outstanding tips. I'll look into getting a USB2.0 powered hub.

    this leads me to another question:
    how would I power this in the car? the powered hubs run off of an ac adapter. what voltage does it send to the hub ... 5v?

    thanks for the info!

  5. #5
    Variable Bitrate drait's Avatar
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    Indeed. Usually +5V to the tip and negative to the base, but double-check the drawing on the wallwart just to be sure the polarity is correct.

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    so would I just run the 5v straight from the red wire of the PSU to the hub? someone recommended using a diode ... how do I choose what kind I need?

  7. #7
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    If you're using it to power a hub, the hub should already have protection against back-voltage, so a diode won't be needed. If you decide to not use a hub, any non-zener diode should work.

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