Computer Power User Article - Power & Performance

Power & Performance

Excerpted from:
Heavy Gear
September 2005 • Vol.5 Issue 9
Pages 16-18 in print issue

Power & Performance
Nine PSUs Stressed Out & Tested

With dual graphics cards, blazing CPUs, fans, multiple hard drives, and more, it is a miracle PSUs even work. Well, sometimes they don’t. In general, look for two things when buying a next-gen PSU: EPS12V support and/or NVIDIA’s SLI certification.

EPS12V is an 8-wire update to the conventional 4-wire ATX12V feed dedicated to your CPU. EPS12V is common in dual-processor servers and workstations, which makes sense. If a 4-wire feed can power one CPU core, you probably need an 8-wire feed for two. EPS12V is still overkill on the desktop, but not for long. SLI certification isn’t always a guarantee of sufficient PSU quality, but it’s the best measure we have now to know a PSU can meet near-term dual-graphics needs.

Our concern here is the +12V rail. To meet 18A safety limits on the number of amperes that can reach a user-accessible contact, the +12V line is split within the PSU. Thus, specs show 12V1, 12V2, etc. Older ATX 1.0 PSUs featuring 20-wire ATX power connectors only have one 12V line — inadequate for a performance-hungry world. Even a PSU with two 12V rails doesn’t guarantee the total amperage is sufficient for an enthusiast configuration.

How We Tested

My primary focus was stability and not silence. In some ways my testing exceeded NVIDIA’s SLI-certification process. For example, NVIDIA generally tests with one hard drive; I tested with four for a heavy draw during startup. These drives average about 1A each on the +12V rail. Two 6800 GT cards add about 24A on the high side. My 3.8GHz Intel P4 570 packs another 12A, for roughly 40A across all +12V rails. Some PSUs only spec 38A on the +12V but perform fine, denoting a healthy margin of conservatism. Other vendors appear to be fudging their numbers a bit. Intel specs for DC output require an 11.40V minimum and 12.60V maximum on a +12V rail and 4.75V min and 5.25V max on the +5V rail. All our PSUs fell well within these ranges.

My test platform had an ASUS P5ND2-SLI motherboard, four 512MB PC2-5400 modules, a 16X DVD burner, and Intel’s Prescott reference heatsink. I took continuous voltmeter measurements during three periods, the first from power on to idling on the Windows XP desktop. The second was a 30-second span of Desktop idle. The third was the period from moving from idle to loading Prime95 and then launching, completing, and exiting 3DMark05’s Return to Proxycon game. By hammering the CPU and SLI subsystems, I aimed to maximize strain on the +12V rail.

by William Van Winkle

PC Power & Cooling 850 SSI
$469
PC Power & Cooling
www.pcpowercooling.com
CPU Rating: 4.5

After testing this unit, I found myself muttering, “Yess, my preciousss . . .” This is the one PSU to rule them all, outfitted with 850W of continuous fury and four 17A +12V rails. Yes, it costs more than some PCs and may require a different chassis to meet its dimensions, but the 850 SSI’s MTBF is triple that of most competitors, and you get six SATA and eight Molex connectors on abundantly long, fully black mesh wrapped cable bundles. In the top tier of PSUs for stable voltage regulation, the 850 SSI defaults to nearly perfect voltage levels. Looking at test results, you might conclude that this unit is on par with Antec and OCZ, but it’s in a league by itself. Just pop off the cover and compare the size and amount of circuitry in this tank with any other PSU. The 850 runs quietly, efficiently, and with nary a ripple. You won’t find a more future-proofed PSU for sale today.