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  1. #1
    mean eating machine ronyville's Avatar
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    Default Power Supply Voltage fluctuation

    I have an intel motherboard running xp pro, P4, 1GB Ram. The motherboard has a utility which monitors temperature and voltage. The +12V keeps fluctuating up to 12.313V. So I reckon its time I got a new psu cos this could damage my computer. Anyone out there thinks thats this is normal or has a better idea about doing something about the fluctuation than I would love to hear about it.

    cheers

  2. #2
    Smiling Down On Youse SurferJoe46's Avatar
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    Default Re: Power Supply Voltage fluctuation

    I just looked at my SmartGuardian, and it shows a slight fluctuation too...but I have to believe that it's WNL.

    I imagine there are loads and unloads going on all the time on that buss, and that the actual voltages are not outside normal parameters anyway.

    My rate on the 12v buss is 12.19 to 12.29, which has been the case since I've owned this unit..over 3 years now.


    Warum werden wir so früh alt und klug so spät?

  3. #3
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    Default Re: Power Supply Voltage fluctuation

    AFAIK most things in the computer that use raw 12v are motors and would tolerate small variations. The important things like the CPU use the 12v after it has been through a precision voltage converter down to something under 2v. Voltages reported by the motherboard aren't that accurate anyway.

  4. #4
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    Default Re: Power Supply Voltage fluctuation

    I have a ASUS MB and the 12v, 5v legs fluctuate slightly due to load like someone above mentioned. The 3.3 and Vcore are steady. This is normal so I wouldn't worry. My 2cents+gst

  5. #5
    Smiling Down On Youse SurferJoe46's Avatar
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    Default Re: Power Supply Voltage fluctuation

    <........due to load like someone above mentioned.....>


    Wow! I've graduated to "someone" now!


    Warum werden wir so früh alt und klug so spät?

  6. #6
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    Default Re: Power Supply Voltage fluctuation

    The 5V and 3.3V are fairly critical. They are usually specified to be +/-5%
    and the other supplies are allowed to be +/- 10% or 15%. COU coltages are usually governed by motherboard regulators. 12 volt is iued only for motors in disks and fans (and serial ports). None of these loads needs close regulation.

    I'm not sure about ATX supplies, but on PC and AT supplies only the 5V is regulated. The levels of the other supplies are determined by the number of turns each has on the transformer. The 5V might be a centre-tapped 6 turn winding, whereas the 12V might have a centre-tapped 10 turn winding. The voltage drop in the diodes and chokes will cause the 12V to drop with increasing load. The switchmode regulator chip gets its feedback from the 5V supply, so if its load varies, the 12V might go up and down because of that too.

    Worry if your 12V goes to 0V.

    Who says the measurements aren't accurate? I put in a programme to show the voltages, and it gave me about 15 digit values. They were totally meaningless, but they were to 15 places.

  7. #7
    tweakedgeek tweak'e's Avatar
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    Default Re: Power Supply Voltage fluctuation

    the sensors are very accurate. however the fluctuation is the thing to keep an eye on. they normall fluctuate a little bit. to much is a sign of a power supply failing or struggling to supply. one thing to keep an eye on is sudden dips in power. also the 5v is often tied to the 12v rail, if the 5v dips it causes the 12v to go high.

    what sort of PSU have you got? if its a cheap pos then it would be worth changing it.
    Tweak it till it breaks

  8. #8
    mean eating machine ronyville's Avatar
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    Default Re: Power Supply Voltage fluctuation

    Its a 400W ATX psu, i bought it new with the case a few months ago. I wasnt too sure wheather it was normal for it to fluctuate like that.

  9. #9
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    Default Re: Power Supply Voltage fluctuation

    The sensors are not accurate. They might be "precise" because they give "digital" numbers. But they are not as accurate as a $5 multimeter. They don't have to be, and it would cost money.

    It's normal for the 12V to vary. That does no harm.

  10. #10
    tweakedgeek tweak'e's Avatar
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    Default Re: Power Supply Voltage fluctuation

    yes its normall but it depends what normall for your pc. sorry but its sometimes hard to tell if its just normall fluctuations or ones casued by a fault. i've had faulty PSU's that looked like normall......untill i put a good one in and saw the difference.

    whats the brand of the PSU ?

    also whats the specs of the pc? the psu might be a bit light.
    Tweak it till it breaks

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