DC Power Gains Footing in Data Centers

By Ed Sperling -- 6/21/2006

Newark, Calif.—Thomas Edison may have had the right idea after all. Nearly a century after he lost a nasty corporate battle to push direct current over alternating current, companies are finding that DC current is more suitable for data centers because it costs significantly less money.

Executives gathered at Sun’s Newark facility today to show that swapping one power source for another can cut energy consumption by about 20 percent, which translates into billions of dollars a year in energy savings. That’s only for existing servers, too. New servers being produced by companies such as Sun and IBM for use with DC power can cut power consumption by as much as 40 percent.

The change is one of the most significant to ever hit the data center, which has grown up with a complement of AC and chemical batteries in uninterruptible power supplies (UPS). Mark McGough, president and CEO of Pentadyne, contends the better solution is to replace that with DC-powered equipment, using flywheels to generate additional power the same way they do in a hybrid car.

“AC power uses transformers to start up, down, invert and rectify—all of which generates heat,” said McGough. “If you use fewer of those devices, you have less heat, less power loss and more reliability.”

The heat issue is particularly acute with new blade servers, which are extremely thin, rack-mounted machines working in close proximity to each other. Cooling them is a requirement, but it is less of an issue in DC-powered server farms because there are fewer devices converting power back and forth in the server room. In addition, DC power runs cleaner than AC, which is prone to power surges.

In the typical data center, the power distribution system converts 480-volt AC power supplied by the utility company through a transformer that steps it down 208 volts. From there, power supplies convert it to the appropriate DC voltage. All of this happens with a significant loss of power through heat, however.

There already are servers on the market that can run at 48 volts DC, which is the standard in the telecommunications industry. By skipping or consolidating conversion steps, this approach can save as much as 20 percent of electricity usage while eliminating unnecessary heat generation. The result also is a gain in available floor space, which is another key cost for server farms and one of the limiting factors for expansion.

Ironically, the approach is one that Edison advocated nearly a century ago, although for entirely different reasons. Edison pushed DC power because it was safer than AC, using a invention that became known as the electric chair as proof that AC was dangerous. AC ultimately won the battle because of its ability to be distributed over larger distances, but in localized settings such as a data center cost the issue is cost and heat loss rather than transmission.

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