negative voltages...

[Taurus]

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.

 

[Zedric]

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 ).

 

[XP Abuser]

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

 

[GoNz0]

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.

 

[Taurus]

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?

 

[jumpy]

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...

 

[Maveric169]

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.

 

[Zedric]

Originally posted by Maveric169
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.

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.

 

[XP Abuser]

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

 

[GoNz0]

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

 

[Zedric]

Originally posted by XP Abuser
devices like fans hdds, cd drives use the 12 v rail

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.