Computer Build Resource Thread - Page 627

On October 04 2011 16:03 skyR wrote:


The total is listed on your label. Typically a 1200w unit will have around 100a and a 1000w unit will have around 82a on the 12v rail(s).

On October 04 2011 16:17 skyR wrote:
No. Power is not distributed evenly across the rails nor will you ever max out the multiple rails. Each connector is assigned to specific rails so usually the CPU /motherboard is assigned to a rail, molex and sata to another rail, and each set of PCIe gets their own rail.

On October 04 2011 16:30 Legatus Lanius wrote:
i like techpowerup for power usage. they show the actual wattage from the graphics card rather than the whole system, and have a bunch of different stress factors.

http://www.techpowerup.com/reviews/HIS/Radeon_HD_6970/27.html

'peak' is usually closest to what you'd experience in-game, so give or take 200w for each gpu assuming they all have equal performance?

+ all the other components

On October 04 2011 17:09 Legatus Lanius wrote:
no idea cabron

On October 04 2011 17:26 jacosajh wrote:
Like how a PSU can have 430W total, but 120W across the 3.3V (20A) and 5V (20A) total, and 336W (28A) on the 12V.

The 3.3V and 5V don't add to 120W
And the 12V doesn't add to 430W

does it?

This is a CX430 V2 btw

There are a lot of places that explain this -_-

On October 04 2011 17:35 Legatus Lanius wrote:
i think they are just designed high to run power hungry cards off the one rail. wouldnt make much sense if each rail totalled the max wattage but was too low to supply power to a gtx 480 or w/e

1200w unit will have around 100a

100a and a 1000w unit will have around 82a on the 12v rail(s).

You may think that the maximum amount of power a power supply can deliver is simply the sum of the maximum amount of power each output can deliver. In truth, the math isn’t that simple because of the way PC power supplies work internally. The main positive outputs (+12 V, +5 V and +3.3 V) share some components, so even though each output has an individual maximum output, this maximum can only be reached when no power is being pulled from the other outputs.

The most common case is the +5 V and +3.3 V outputs. Even though they have individual maximum current and power limits, these maximum values can only be pulled when no power is being pulled from the other output. Together they have a combined maximum power, which is lower than the simple addition of the maximum capacity from +5 V and +3.3 V outputs.

For a practical example, consider the power supply in Figure 29. Its label says that the +5 V output can deliver up to 24 A, which equates to 120 W, or 5 V x 24 A. The +3.3 V output can also deliver up to 24 A, which equates to 79.2 W, or 3.3 V x 24 A. The maximum combined power printed on the label is 155 W, (less than the simple addition of the maximum power each output can deliver individually), which would be 199.2 W, or 120 W + 79.2 W.

The same idea holds true for the +12 V outputs. On the power supply from Figure 29, each +12 V rail can deliver up to 16 A (192 W, or 12 V x 16 A), but the maximum combined power for the +12 V outputs is 504 W, not 768 W (192 W x 4).

And finally, we have a combined power for the +12 V, +5 V and +3.3 V at the same time, which isn’t a simply addition of the maximum combined power for the +5 V/+3.3 V outputs with the maximum combined power for the +12 V outputs. On the power supply from our example, the maximum combined power for these outputs is 581.5 W and not 659 W (155 W + 504 W).