Understanding Power Supplies.........

[madwelshboy]

Hi all,

I am getting quite a bit of fluxuation on my 12V line off my QTEC 550W. I am trying to understand what devices run off a 12V connector.
Am I correct in assuming Hard Drives, CD/DVD Drives, 4pin Case Fans all take juice off the 12V ? (If I have missed something please let me know).
So what devices run off the 5V supply, PCI cards etc?
Also, I am trying to improve my 12V when overclocking (as it dips to 11.74 when @ full throttle ), do you think by changing to 3pin case fans it would help?? Any input appreciated.

[eldren]

Ditch the Qtec, get an Antec. Solved.

[Lexeus]

I think 3 pin connectors draw off the same as 4 pin molex connectors, they just have a different connector, with one extra wire, the sensor.
I dont really know much about which devices use which voltages, but the red wire on the 4 pin molex's is a 5v line, and the yellow wire 12v, so maybe the drivers use both ?

Also where are you getting those voltage readings from, is it a windows ? As it may not be accurate, the best way is to stick a multi-meter right in the 4 pin molex plugs and get a direct reading. I found that the windows reading of about 11.4/5V and 5.4V was wrong, and was actualy about 11.8/9 and 5.6V. Im not sure how you can check the 3.3v line ... that itsn't output on any accesible plugs, myabe only through the ATX conector, i dont know.

[Steve]

Right...

5V is used for devices like PCI cards, a lot of the circuitry on the motherboard, and the controller circuitry for drives.

12V is used for motors, fans and devices that take a lot of juice (eg powerful graphics cards.) It might also be used for CPU/memory circuits fred through mosfets and caps - not sure about that though.

The 3.3V line is mobo stuff again - they're the orange cables on the ATX connector.

5V is probably the most important when it comes to overclocking - a lot of circuitry relies on it. 12V is a bit difference. The ATX standards tolerance for 12V is +/- 10% whereas it's 5% on other lines. As long as you're above 11 you should be OK really.

Still, Antec PSU's are the ones to go for, because they have separate circuits for the 3.3, 5 and 12V rails - unlike other PSU's which simply use one or two and "share" them.

[madwelshboy]

Thanks unts (and the rest of the guys for your comments), I wasn't quite sure, thanks for clarifying. So 11.74 on a 12v rail should be ok? My 5v doesn't drop below 4.96 .......

[Agent]

Originally posted by madwelshboy
Thanks unts (and the rest of the guys for your comments), I wasn't quite sure, thanks for clarifying. So 11.74 on a 12v rail should be ok? My 5v doesn't drop below 4.96 .......

It should be, but seriously look at getting a better PSU. Q-tec are one of the worst makes out. Known for unrelability.
Use the search feature at the bottom and you'll see a few threads on them

[SilentDeath]

Still, Antec PSU's are the ones to go for, because they have separate circuits for the 3.3, 5 and 12V rails - unlike other PSU's which simply use one or two and "share" them.

not sure what you mean by that.. but most power supplys use different windings on the secondry coil of the transformer for different voltages... 3.3, 5 and 12v are all serperate...

[chrisf6969]

My voltage has always been out of wack and my computer is rock solid/stable.

[Enverex]

Those voltages are all fine, so there isn't any reason why it would be unstable. 3.3 is still safe, and not important anyway, 12v is well within limits, and the 5v being higher will help keep your system more stable when overclocking...

NS

[blockers]

What about the minus rails?

There is the -12v one at -8.25v is that ok or not?

Time for me to download sandra again

Will

[madwelshboy]

Hey chrisf6969,

Nice to see you again, great clock, good to know. Thanks.