View Full Version : PC Power Supply Fluctuations - OK or not?

12-04-2002, 12:25 PM
I have a second PC (for the kids) with a 300W PS, running XPpro on AMD Duron 950 w/128MB ram. It has been running just fine. I just installed MBM5 on this PC, more out of curiosity than any real need, and immediately began to get voltage alarms on +5 and +12v, all others rock solid. Logged 1000 data points @ 20sec increments. +5 ranged from 5.15-5.21v, with 8 spikes down to 4.31v. +12 ranged from 12.46-12.52, with 30 spikes below 12.20 and 13 above 12.65. Should I be concerned?

12-04-2002, 12:41 PM
Should be ok - a half volt over is no problem. Undervoltage can generally be coped with by the capacitors in the PSU. The easiest thing to do is to fit a surge-suppressor to the mains plug, which will iron out the peaks and troughs that occur throughout the day.
If it gets too much, then the PSU may be getting a little old (the smoothing capacitors may not be able to keep up with the spikes) Unless you're happy about replacing these (Don't touch it unless you KNOW what you are doing) then simply replace the PSU - they're pretty cheap.

12-04-2002, 12:53 PM
Thanks for the reply. PSU is new, less than 60 days old. I'm not too freaked, just curious.
Most concerned by the down spikes in the +5v line, from 5.2v all the way down to 4.3v - that's a pretty big spike percentage-wise.
Also, exactly what voltage is measured? Do the BIOS voltage sensors measure PSU output, or actual on-board voltages?

12-05-2002, 06:28 AM
exactly what voltage is measured? Do the BIOS voltage sensors measure PSU output, or actual on-board voltages?
That's a very good question. I've always been led to believe that was the PSU output voltages, but I could be wrong.

You say this PSU is only 60 days old? It isn't an OEM or generic PSU by any chance, is it? Those voltage spikes aren't really any big deal, but they are slightly beyond what even my pathetic 300W PSU is giving. And chances are good that if it's new, it will always give swaying voltages for the rest of its lifetime. It may be a good idea to buy a decent name-brand PSU for that PC, but if it runs fine then who cares? :D

Good quality name-brand PSU's will generally be able to keep voltages within 10-15%. Some high-end models, like PC Power & Cooling's expensive ones, promise a mere 1-2% deviation. Antec, Enermax, Enlight, Sparkle, and PC Power & Cooling are all good name-brands for PSU's. A 300W shouldn't cost you any more than $35-40.

12-05-2002, 09:28 AM
Thanks for the feedback, your vacation is approved.:cool:

The PSU is an Antec. If you are correct, and the voltages that are being measured are PSU output, which is then "smoothed" by the motherboard capacitors, I really don't have anything to worry about.

At this point, I plan to leave it as-is. Thanks again!

12-05-2002, 11:42 AM
One option is to use a UPS to smooth out the power going into the power supply. I recently saw one advertised for about $30 (strangely enough at Home Depot or Menards - I forget which) that gave you 15 minutes of power in a power failure. For that price, it can be a good investment and will help your components live longer.


12-05-2002, 09:08 PM
Antec is quality type equipment.

Not knowing which Mboard you have

MBM working with the readings could

be partial incompatability with sensors.

Do you have H/W monitoring section in BIOS?

Might monitor the voltage readings there

for a time and catch some readings. Probably

be more accurate.