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Power Supply Requirements

About once a week I hear someone try to explain that they need a 1000w power supply for their home PC. My common correction is usually that they “want” or “think” they need one.

There are very few builds that would require such a large power source. It would be nice to have that flexibility and available power, but I guarantee anything short of a quad-fire or tri-SLI (4 ATI GPU’s, or 3 nVidia GPU’s) is not going to need that much power.

Quad-core CPU’s coupled with a half dozen hard drives barely equal the power of a single high-end gaming graphics card; And that would only happen if you were accessing all those hard drives at once!

Then why do they make them? because, yes there are computers that need them. But, I also believe there is a misconception that is spread to consumers…

First of all, video card manufactures like to tell you you need a minimum hardware specification of a power supply (example, a 5870 found on XFXforce.com) of 500w. Now, most people look and see 500w and go “Hey that sounds pretty reasonable”. But take into account that XFX’s legal department would of had their fingers in the writing of the specification, taking into account people with tier one built computers (such as Dell, HP, Gateway, etc…) who use generic PSU’s.  I won’t go into detail how generic PSU manufacturers  calculate their wattage vs name brand, but I have have seen 5870 video cards run off of  450w name branded psu’s with overheard.

Now, what if you wanted two 5870 video cards in crossfire? does that mean you need 1000w PSU? No.

The 500w PSU requirement was taking into account for generic PSU’s and for quad-core setups with more than 4gb of ram, and multiple hard drives and optical drives.

This page here (new window will open) shows a user who had dug up that a 5870 (at the time of this writing, the most powerful single GPU ATI video card on the market) uses a maximum 188w under full load. Full load is typical to ran at when running benchmarking; for gaming and every day use, you will most likely NEVER reach this level use).

We would at MOST need a 688w GENERIC PSU. With that being said I know someone who is currently running a 1366 based core i7 960 cpu, with 12gb of ddr3 ram, two raptor drives in raid 0 and a mass storage hard drive and bluray burner, with two 5870 videocard in crossfire all on a 550w Enermax PSU! Honestly I think this is pushing well over the limit, however I would not sweat to put the same setup on a name brand 650w PSU, just by going by the manufacturers requirements and the power usage of the 5870.

Now lets look at two 5870 video cards in Quad-Fire (4-way crossfire). 3 x 188w = 564w; 500w (XFX recommended) + 564w = 1064w on a Generic PSU. I don’t think a generic 1000w PSU exists, but a name brand 1000w PSU will handle the full load. So, if you are willing to dish out for FOUR 5870 video cards, you MAY require a 1000w PSU.

However, running a quad-fire video card setup with 5870’s like this will almost be impossible to run at its full potential unless you were using SSD hard drives, and newer small circuit technology CPU (32nm is the smallest circuitry CPU’s available at this time of writing) and ddr3 memory (which is more energy efficient that ddr2) which are all less power hungry than older hardware. Lessening the need to have a 1000w psu.

Want to see what you need? here is a calculator from Antec.
http://www.antec.outervision.com/PSUEngine (This will open a new window)

Keep in mind that this is a power supply manufacturer. They will not steer you towards a lower than required PSU, and if anything will pad the PSU requirement a bit. They even have options to pad it yourself!

Note: I did not talk about nVidia Video cards (the new Fermi based video cards are very new and I have no experience using them), and was taking into account only the new 1156, 1366, and am3 CPU based systems using DDR3 ram; Also since less motherboard manufacturers are providing IDE controllers and IDE based drives are more money than SATA drives, keep in mind that IDE drives draw almost double the amount of power than IDE. However older technology systems draw just as much as newer technology PC’s :P



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