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Sharing power supply across electronic devices

Discussion in 'Electronic Basics' started by Ian Clowes, Oct 28, 2003.

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  1. Ian Clowes

    Ian Clowes Guest


    I have a device with a 2.5" IDE laptop hard disk in it. I temporarily
    want to put a 3.5" device in there, just for a few hours.

    I can sort out the data signalling using adapters I have, but also
    need to power the 3.5" drive.

    The target box has 5V for the laptop drive, but doesn't have a 12V
    line as needed by the 3.5" drive. I don't want to alter the PSU to
    add one at present.

    Q: Can I run the drive from the power supply of a nearby PC without
    any problem?

    These are the issues I can think of...

    1) AIUI, a 3.5" IDE used 12V for drive power, and 5V for logic.
    Should I use the target device's 5V to ensure the data levels are OK
    at both ends? I would then use just the 12V from the PC supply.

    2) Should I tie the chassis and/or 0V lines of the two PSUs together
    for any reason?

    3) I have a spare PC chassis around that I might use. I read
    somewhere that the PSU needs a minimum load to keep it sweet. Is this
    true? If so can I just leave the motherboard connected without
    worrying whether it actually boots, etc?

  2. Ben Weaver

    Ben Weaver Guest

    Hi Ian...

    In my experience:

    1. Doesn't matter who supplies what, as long as 5V gets 5V and 12V gets
    12V - bearing in mind that...

    2. Tie the grounds together. Otherwise one might float.

    3. Yes indeedy. Just shove a mobo or spare hard disk on any PSU to keep
    it happy. Might not turn on otherwise.

    *ALSO* make sure you turn all the PSUs on and off at the same time. I
    find that HDDs don't like having 12V with no 5V and vice versa.

    Have fun...

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