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j-g-faustus

What are the different power lines (+3.3V, +5V...) used for?

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j-g-faustus    0

I'm trying to figure out which computer components are drawing power from which lines. For example, here is the spec for a Silent Pro M500:

SilentProM500-6.jpg

I suppose this means that you can kill this 500W power supply with a load of slightly more than 6W on the -12V line.

Does anyone know of a reference to what the different power lines are used for in a modern PC, so I can calculate e.g. how many hard drives or how much video card the PSU will support?

The reason I'm asking is that I have a Silent Pro M500 that died; and in its short lifetime (a couple of hours) it never drew more than 125W from the wall (more details) as measured by a home wattmeter (similar to a Kill-a-watt).

I'm trying to track down what happened, and also to learn more about how to "right-size" a power supply.

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I'm trying to figure out which computer components are drawing power from which lines. For example, here is the spec for a Silent Pro M500:

SilentProM500-6.jpg

I suppose this means that you can kill this 500W power supply with a load of slightly more than 6W on the -12V line.

Does anyone know of a reference to what the different power lines are used for in a modern PC, so I can calculate e.g. how many hard drives or how much video card the PSU will support?

The reason I'm asking is that I have a Silent Pro M500 that died; and in its short lifetime (a couple of hours) it never drew more than 125W from the wall (more details) as measured by a home wattmeter (similar to a Kill-a-watt).

I'm trying to track down what happened, and also to learn more about how to "right-size" a power supply.

Hi,

In response to your thread title.

Read up! :)

http://en.wikipedia.org/wiki/Power_supply_rail

It also would help if you furnished us with your computer specs.

nickt1862

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j-g-faustus    0

Thanks :D (I found the Wikipedia ATX page earlier, but not this one.)

So to the best of my understanding:


  • [*:jsze1n7h]+12V: CPU, graphics cards, fans, PCI-E cards
    [*:jsze1n7h] +5V: hard drives, optical drives, PCI cards, USB
    [*:jsze1n7h]+3.3 V: RAM, misc. motherboard
    [*:jsze1n7h]-12V: serial port
    [*:jsze1n7h]+5Vsb: power under "soft off"/standby to the circuits that handle "wake on LAN", "wake on keyboard" and similar

Edit: Updated listing

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j-g-faustus    0
It also would help if you furnished us with your computer specs.

CPU: Intel i7 2600K

Mobo: Asus P8P67

RAM: 2x4GB Corsair Vengeance 1600 MHz, 1.5V

GPU: Asus EN210 Silent

Disk: Corsair 60GB SSD + Samsung 250GB HDD

CPU cooler/fan: Noctua NH-C12P SE14

Case fans: 1x120mm (the one included with this case) + 2x80mm (Fractal Design Silent Series)

PSU: Cooler Master Silent Pro M500

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Thanks :D (I found the Wikipedia ATX page earlier, but not this one.)

So I guess the only thing missing is what the 3.3V is used for. Some obscure circuitry on the motherboard?

You're quite welcome.

Now why your power supply quit could be either not enough power supply output and or just a bad power supply.

AC wall outlet draw and DC Watt current then generated from a power supply are two different things unless the wall outlet is not putting out the minimum current needed to run such power supply correctly - which doesn't seem to be your scenario.

There are power supply calculators if you google for them and it's always best to purchase an 80 plus rated power supply and as many rated Amps you can afford especially under the 12+V line(s)/rail(s) - the more Amps the better.

There's more here that explains some (copied below) about the 3.3V: http://www.pcguide.com/ref/power/sup/func_Voltages.htm

"+3.3 V: The newest voltage level provided by modern power supplies, it was introduced with the ATX form factor and is now found on the ATX/NLX, SFX and WTX form factors. It is not found in Baby AT or older form factors. Originally, the lowest regular voltage provided by the power supply was +5 V, which was used to provide power to the CPU, memory, and everything else on the motherboard. Starting with the second generation Pentium chips, Intel went to a reduced 3.3 V voltage, in order to reduce power consumption as the chips got faster. This required motherboard manufacturers to put voltage regulators on their boards to change the +5 V to +3.3 V. The regulators produced a great deal of waste heat and having to do this reduction on the motherboard was very inefficient, so now the power supply provides +3.3 V directly. It is used to run most newer CPUs, as well as some types of system memory, AGP video cards, and other circuits."

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j-g-faustus    0

Thanks again ;)

Although the PCGuide says that the CPU runs off the 3.3V starting from second generation Pentium (that would be Pentium II, I assume), while Wikipedia says that the CPU runs off the 12V starting from Pentium 4.

I assume that Wikipedia is the most up to date here, and that CPUs run off the 12V rail today. (Also supported by the fact that modern PSUs only supply a relatively limited amount of power over the 3.3V rail: 66W for the Silent Pro M500 (3.3V * 20A), which wouldn't be enough to run any desktop Core i7 with their TDP in the 95-130W range. Even the Silent Pro Gold 1200W doesn't have more than ~73W on the 3.3V rail.)

If we exclude AGP video cards as well, as they hardly exist anymore, we're left with "some types of system memory" (RAM, I assume?) and "other circuits" that are currently powered by the 3.3V rail. I'll accept that as a working hypothesis :)

OK, thanks for your help - I know quite a bit more about power rails now than I did a couple of days ago.

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