why my voltage fluctuates??

[helloguy]

i'm monitoring my 5v,12v and 3.3v of my mobo,and i noticed that it isn't stays on a fix number,for example,my 12v reads 12.20v,12.30v,it keeps changing..why's that?? and another thing is....when i set vcore to default(1.75 on my xp1800) , my 5v is dragged down to 4.8?v,if it were to set to 1.65v,it reads 4.9?v ..any ideas??

 

[Adul]

powr supplies will normal fluctuate. that is why they use capaciters around the cpu. to stablize the power.

has for it dropping .1 volt, i think that is still in spec, and the readings have a small margin of error has well.

if you athlon can run stable at a lower voltage stick with it. 🙂

 

[PowerEngineer]

Well, an "ideal" power supply maintains a constant output voltage regardless of the current being drawn from it. While that's the characteristic PC power supplies have as a goal, none (especially given the price we're willing to pay) actually achieve it. A better representation of a PC power supply is an "ideal" (i.e. constant) voltage source with a small resistance in series. At zero current, the voltage at the terminals of the power supply will equal that of the "ideal" source. But as the current drawn from the power supply increases, there's an increasing voltage drop across the internal series resistance. This means that the voltage measured at the terminals of the power supply will drop as the current increases. Of course, better power supplies have smaller internal resistances and therefore smaller voltage drops as a function of load (current).

Because raising your vcore increases the current drawn by your chip from the 5v power supply, it's not really surprising that causes the power supply voltage to drop. You should also see fluctuations in the 12v supply voltage as hard drives and CD drives spin up or spin down, etc. These voltage drops last as long as the loading. As Adul observed, the capacitors on the board help smooth out the harsher voltage spikes, but these voltage drops generally persist well beyond the time constants associated with the capacitors (and their resistive equivalents) so that I think your CPU does in fact see these lower voltages in a small fraction of a second.

 

[Locut0s]

Interesting I have a similar thing with my system. I'm running an Athlon 1800+ system with a Soyo K7V Dragon Plus Mobo and an Enermax power supply. On my system if I take a look at the voltages with the utility "SmartGuardian", supplied with the mobo, I notice that the +/- 12V lead fluctuates a LOT! I mean by as much as over 1 V! However all the other voltages seem to fluctuate much less, like about 0.2v. I have often suspected the reason for this is that the 12V connector form the power supply is not plug into anything, the K7V Dragon Mobo does not have a 12V connector. Everything on my comp seems to run fine so I have stopped worrying about it.