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View Full Version : Do I need a new PSU?


DoomUK
09-23-05, 08:10 PM
Well, my 12v rail (monitored using ASUS Probe) reports my 12v rail @ 11.7 idle, drop to 11.5-11.6 under load. Should I be worried about this (because I am already lol)? Note that while running HL2, Doom 3, RTHDRIBL and the like I get the occasional 'stutter' (which I never used to get with a single GTX w/ same drivers btw, eliminating the chances of a mere software bug in my opinion).

So, do you guys think that a new PSU is in order? I was looking at the OCZ PowerStream family, check out the 600w in particular: http://www.overclockers.co.uk/acatalog/OCZ.html.

Thanks.

Peoples-Agent
09-23-05, 08:18 PM
Hmmm, I really don't think thats whats causing your problem tho m8, 560 watt is pretty hefty. Hmmm....

DoomUK
09-23-05, 08:31 PM
It's common knowledge that the Watt rating for PSU's is not to be relied upon... A high quality 450w could be more stable/reliable than a ****e 550w.

Although this has nothing whatsoever to do with my problem*, it's to be noted that the exhaust fan makes an annoying clicking noise from time to time... Have to take a look @ it.

*Actually that might have something to do with it- a slowly failing fan causing overheating.

toxikneedle
09-23-05, 09:30 PM
Your PSU has 22A on the 12v rail

Nvidia recommends at least 34A for an SLI system....

BTW, I'm getting the OCZ 600w Powestream for my sli system. Whether or not ur PSU is failing..... I dunno, if you would get BSOD or random freezes, shutdown then that could be a sign of an instable PSU. If you got the money though, I'd probably say... upgrade.

Rytr
09-23-05, 10:18 PM
I guess this is worth repeating...

"It is critical that systems with high-end graphics cards, such as the GeForce 6800 Ultra and GeForce 7800 GTX, are matched with an adequate power supply to ensure stable operation. Therefore, the following power supply information is provided, which originated from NVIDIA's GeForce 7800 GTX GPU Reviewer's Guide:

The GeForce 7800 GTX requires a stable, 12-volt power source for best performance, reliability, and enjoyment. Many PC power supplies dedicate most of their 12-volt power to the power rail that goes to the CPU, rather than the peripheral connectors. Many power supplies also do not provide ample overload protection to protect system components such as motherboards and graphics cards.

For a SINGLE GeForce 7800 GTX graphics card, NVIDIA recommends a power supply with at least 350W, 22amps on 12V. For a DUAL SLI GeForce 7800 GTX graphics configuration, NVIDIA recommends a power supply with at least 500W, 30 amps on 12V. A list of SLI-certified power supplies can be found at SLIzone. Due to power distribution limitations of the PCI Express bus, GeForce 7800 GTX boards require a separate PCI Express power plug on the back end of the card."

DoomUK
09-24-05, 04:51 AM
Thanks guys, my mind is made up now. A new PSU it is :).

Peoples-Agent
09-24-05, 05:30 AM
Do let us know whether that turns out to be the problem m8.

jAkUp
09-24-05, 12:00 PM
Yea 11.50V under load is not very good. ATX spec is 11.40V, but I don't recommend anything that dips below 11.60V under full load.

On all the powersupplies I have tested, the PC Power and Cooling seems to be the closest under full load, dipping to only 11.95V! Enermax's and Antec's are around 11.80V.

john19055
09-24-05, 09:47 PM
The 600ultra's and the 7800GTX need lots of power to run stable and the SLI's need that much more ,It is best to buy the highest power supply you can find and one with High amp rateing on the 12v line,I have had good luck with my power Stream ,but it is always best to buy a High Quaility power supply when running two video cards as far as that goes you need a HQ one just to run one.

AthlonXP1800
09-24-05, 10:14 PM
Yea 11.50V under load is not very good. ATX spec is 11.40V, but I don't recommend anything that dips below 11.60V under full load.

On all the powersupplies I have tested, the PC Power and Cooling seems to be the closest under full load, dipping to only 11.95V! Enermax's and Antec's are around 11.80V.

Hmmm I thought numbers lower than the spec are very good and any numbers are higher than the spec are very bad. About a year ago my friend experienced problems with his PC, it was unstable, he had Q-TEC 550W PSU and I told him to try out SpeedFan software to check all the voltages numbers, all numbers were higher than the spec, his 12V were around 13.5V. I thought these numbers were bad and told him it time to get a new PSU, he went and bought Antec TruePower 480W PSU and then all the problems had gone away.

Anyway I checked my new Antec TruePower II 550W PSU 12V under full load are 11.97V, I am surprise that are very good number, it higher than your PC Power and Cooling PSU. :)

Rytr
09-24-05, 10:17 PM
You don't have to buy the most expensive, you just have to buy one that is quality built and meets SLI requirements. Here's the list of the ones Nvidia has given certification: (from the site mentioned in my previous post)

Antec TPII-550
Antec TP2550EPS12V
Antec TrueControl II 550

Enermax EG565P-VE 535W
Enermax EG651AX-VH EPS12V 550W
Enermax EG851AX-VH EPS12V 660W
Enermax EG701AX Noisetaker 600W

PC Power & Cooling Turbo-CoolŪ 510 SLI (510ATX-PFC)
PC Power & Cooling Turbo-CoolŪ 850 SLI (850ETX-PFC)

Seasonic S12-600 Watt

Silverstone ST65ZF 650W
Silverstone ST60F 600W

Sunbeamtech NUUO Series 550W SLI (SUNNU550-US)

There are others that are not certified but work well. You just have to know which ones. Examples are models from OCZ that use Tagan cores and from FSP. Still, you have to know what you are buying. The FSP, for example, that I have requires purchasing a Molex to 6-pin adapter for connecting the second card as it only comes with one 6-pin connection.

jAkUp
09-24-05, 10:26 PM
Hmmm I thought numbers lower than the spec are very good and any numbers are higher than the spec are very bad. About a year ago my friend experienced problems with his PC, it was unstable, he had Q-TEC 550W PSU and I told him to try out SpeedFan software to check all the voltages numbers, all numbers were higher than the spec, his 12V were around 13.5V. I thought these numbers were bad and told him it time to get a new PSU, he went and bought Antec TruePower 480W PSU and then all the problems had gone away.

Anyway I checked my new Antec TruePower II 550W PSU 12V under full load are 11.97V, I am surprise that are very good number, it higher than your PC Power and Cooling PSU. :)

It depends on what you consider full load. Higher numbers are bad, lower numbers are bad. You want as close to 12v as you can get. Most decent PSU's dip to about 11.85 under intense load.

acrh2
09-24-05, 10:34 PM
Hmmm I thought numbers lower than the spec are very good and any numbers are higher than the spec are very bad. About a year ago my friend experienced problems with his PC, it was unstable, he had Q-TEC 550W PSU and I told him to try out SpeedFan software to check all the voltages numbers, all numbers were higher than the spec, his 12V were around 13.5V. I thought these numbers were bad and told him it time to get a new PSU, he went and bought Antec TruePower 480W PSU and then all the problems had gone away.

Anyway I checked my new Antec TruePower II 550W PSU 12V under full load are 11.97V, I am surprise that are very good number, it higher than your PC Power and Cooling PSU. :)

Absolute reading in the bios doesn't mean jack. Most of the time, people whose voltages read 11.7, 12.0, or 12.2V don't realize that in all those cases, the true reading is 12.0volts (+-0.05V) at idle. The reason for this is that the motherboard sensors aren't accurate, and the same power supply can give all these different readings when used with different motherboards. The only reliable way to obtain voltages is to measure them directly with a multimeter.
However, motherboard sensor readings aren't entirely useless. While they won't provide you with information on how close your system to ATX specs, they will give fairly accurate results with respect to how much the voltage will drop under load.
For example, jAkUp's PSU, if I read his post correctly, will drop from 12.00V at idle to 11.95 under load. Or my own PSU, the same as jAkUp's, will drop from 12.22V at idle to 12.16V under load. That's only 0.05-0.06V drop on the 12V line. Your own PSU gives a reading of 11.97V. But ask yourself, how much did it drop? Was the reading before applying load 12.2V? In that hypethetical case, your voltage drop was 0.23V. In reality that would mean (in most cases) a drop from 12.0V to 11.77V on the 12V rail.

By the way, according to a LARGE number of reviews, where actual votages were measured, the PCP&C Turbocool 510w psu's are some of the most stable PSUs you can buy. OCZ psu's of similar power are in the same category. Unfortunately, your own PSU, Truepower2 550, while a decent PSU, is not even in the same league as the Turbocool. Which is one of the reasons why your PSU is about $80 less expensive.