Estimating PSU needs?

[foycur]

I have a home built system (see details below) for which I am using a PSU from CompUSA that is 300 W. When I have ASUS Probe up and running in the background, I am getting two things. A consistent elevation to 15 Volts on the +12V lead, and the +3.3V drops occasionally to 2.9-3.0 (the 15 volt reading has been there from day one; it's always 12 V in the BIOS, but once I boot up the OS it jumps to 15 and stays there). As a relative newcomer to building systems, I have three questions:

1) is there an easy way to 'eyeball' what wattage would be needed for given components?
2) could a defective power supply cause all of these goofy numbers?
3) Should I believe BIOS or ASUS Probe?

Thanks!!!!

 

[Mictlantecuhtli]

No software can adjust the voltage that comes out of PSU, as far as I know. There are a lot of applications that modify the mainboard voltages (AGP, CPU, memory), but not PSU's 5 or 12V rails.

Therefore I think it's a software problem. If you have steady hands and a multimeter, you could measure the voltage straight from any molex connector, yellow wire is 12V, red 5V and black (either) is ground.

One PSU size / wattage calculator is here: http://www.jscustompcs.com/power_supply/

I don't know how reliable that is but it should give some directions.

 

[foycur]

thanks for the info

Thanks a lot esp. for that website. I think my 300 W power supply is inadequate, the program suggests a power supply no less than 310 watts, and I've got a 300 watt power supply. Time to get a new supply!

The Molex connectors are the ones that go to each individual piece of hardware, like HDD and vid cards?

 

[Mictlantecuhtli]

Time to get a new supply!

If the current one works, why?

The Molex connectors are the ones that go to each individual piece of hardware, like HDD and vid cards?

Correct.

 

[foycur]

well, the 3.3 V rail seems to be dropping off to 2.8 or 2.9, and i'm getting 15 V on the 12 V rail. Haven't had the time to get out and pick up a little voltmeter. And lately the MoBo has been giving me problems with rebooting spontaneously, etc. I just think the 300 W PSU is just not enough to do the job with all I've got on there. I've got a 9800 pro card, two 7200 RPM hard drives, a PCI fan card beneath the vid card, two case fans, and soon to be adding a sound card. The MoBo is another issue because the BIOS got corrupted and I cannot flash it, so it's heading back to ASUS for look see. That may be why it's rebooting spontaneously, but I figure a bigger power supply can't hurt esp when it comes time to upgrade, or if they send me a sweeter MoBo.

 

[nein]

well, the 3.3 V rail seems to be dropping off to 2.8 or 2.9, and i'm getting 15 V on the 12 V rail. Haven't had the time to get out and pick up a little voltmeter. And lately the MoBo has been giving me problems with rebooting spontaneously, etc. I just think the 300 W PSU is just not enough to do the job with all I've got on there. I've got a 9800 pro card, two 7200 RPM hard drives, a PCI fan card beneath the vid card, two case fans, and soon to be adding a sound card. The MoBo is another issue because the BIOS got corrupted and I cannot flash it, so it's heading back to ASUS for look see. That may be why it's rebooting spontaneously, but I figure a bigger power supply can't hurt esp when it comes time to upgrade, or if they send me a sweeter MoBo.

Yes, time for a new PS ... Click on quoted words below for pertinent link.

"There're signs of power-supplies being overloaded for one reason or another. One of the most common signs for marginal/in-sufficient 3.3V + 5V combined power is the inverse level up shifting of 12V instead of drooping.

When 3.3V and 5V get loaded down and dropping downward, 12V level will shift upward (-5V and -12V will be more negative!!!)"

 

[foycur]

Update

Nein, just to update you on what happened....I ended up switching out my 300 Watt PSU for a Thermaltake 480 W PSU and the 3.3 V rail problem seemed to get solved. ASUS PC Probe keeps showing my 12 V rail at 15.5 V, but when I go into BIOS it says it's running around 12.2 V. Thanks for everyone here who gave me advice, it was much appreciated. I can't imagine that 480 Watts would be insufficient for my system and cause this 15 volt error. It makes me wonder if ASUS Probe is sort of screwy.

 

[RealBlackStuff]

Look on the ASUS website, they may have an updated PCProbe.

 

[foycur]

Updated Probe is what I needed

Yep, that seems to have solved it. Thanks to everyone who helped me out on here. I have a home built system that I've been tweaking by myself for some time without the benefit of other people to ask questions, so I thank all of you. You have saved my marriage. My wife is tired of me tinkering with the computer, but she doesn't understand that it's a sickness!! Must upgrade, must fiddle with motherboard.........