negative voltages...

Discussion in 'Windows Desktop Systems' started by Taurus, May 25, 2003.

  1. Taurus

    Taurus hardware monkey

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    if my -5v is at, say, -5.44v... what's that mean? my +5v is right in line, but i'm wondering what different negative voltages tell me? i've seen this on more than one comp, so i'm not too worried. just curious. :)
     
  2. Zedric

    Zedric NTFS Guru Folding Team

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    It means you -5V is off by .44V. :) No seriously I don't think it's a problem. The -5V and -12V are only used very little anyway. I don't think .44V makes too much difference. Of course it could also be an inaccurate senser (not top notch you know :)).
     
  3. XP Abuser

    XP Abuser Guest

    yeh voltage sensors are inaccurate at best -- the properties of the chip change with heat causing botched readings
    if you want the most accurate sensor install a smoke alarm in your setup thatll tell you if the voltage is too high but .44 volts is nothing to be alarmed about
     
  4. GoNz0

    GoNz0 NTFS Stoner

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    the 5v rail is not used by the PC unless in the suspend to ram sleep state, and 10% on any voltage is no problem.
     
  5. Taurus

    Taurus hardware monkey

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    thanks guys. just wondering what the -5v and -12v are used for. where do they come into play.

    like i said, i'm not really worried about them being higher or lower than spec because it seems pretty common with the negative voltages. and i'm aware of the low quality voltage sensors on most motherboards.

    and, gonzo... don't drives use the 5v rail all the time?
     
  6. jumpy

    jumpy Guest

    The cpu also draws its power from the 5V rail (except on p4's which use the 12V rail). I have never found out what the negative rails are used for, but I wouldn't worry about it too much...
     
  7. Maveric169

    Maveric169 The Voices Talk to Me

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    I always thought the negitive rails were to keep the electrical "flow" ballanced. With just a general ground a switching PS output would become unbalanced everytime it "switches" and prevents a voltage spike with the negitive voltage draw. But that is a good question, and I have never in all the years working on pc's ever heard an explanation for that.
     
  8. Zedric

    Zedric NTFS Guru Folding Team

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    Hmm, I don't think so, but I'm not and expert in switching power supplies.

    One usage I can think of is on OP-amps. They usually want + and - of the driving voltage.

    The 5V rail is the most used. That's why most of the watts on a PSU is on the 5V rail.
     
  9. XP Abuser

    XP Abuser Guest

    devices like fans hdds, cd drives use the 12 v rail
     
  10. GoNz0

    GoNz0 NTFS Stoner

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    i think laptop hard drives use 5v like the 1 in my zen ?
     
  11. Zedric

    Zedric NTFS Guru Folding Team

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    HDD:s and optical drives use both 5V and 12V. HDD:s use more amps on the 5V than on the 12V if I remember the readouts from my MP3-player project correctly.