Will bad batteries be your undoing?

Your UPS is more vulnerable than you think, so don't neglect your most likely point of failure -- the batteries.

NEW YORK -- The shocking truth about power is that the very thing that's supposed to protect your data center is to blame for most power failures -- the UPS.

According to Robert McFarlane, an expert in data center design and principal with New York-based Shen Milsom & Wilke Inc., the sad truth is that most uninterruptible power supply (UPS) installations are not as reliable as people think.

Conventional double-conversion UPS systems consist of incoming AC power from the utility, an AC to a DC converter and then DC to an AC converter, which then sends the power to the equipment. The battery string typically sits between the converters, charging the batteries as the power passes through.

But if the utility power goes down, or your data center's power equipment malfunctions, those batteries are your last resort for a clean shut down and minimal downtime.

According to McFarlane, who spoke last week during the Data Center Decisions conference in New York, the most common UPS point of failure is the battery.

When an individual battery cell is shorted, the pool of available voltage is lowered. But when battery cells fail to open, which they often do, the entire string provides no power to the UPS, much like a failed bulb in a string of Christmas lights.

The solution is dual battery strings, according to McFarlane.

Another must-have is battery monitoring tools. There are two types. Float voltage reduction lowers the voltage across the battery string and measures battery strength as they kick in power. The second type is voltage addition -- which naturally adds a small, measurable amount of voltage to the string to gauge the battery's strength. According to McFarlane, the choice between the methods is a matter of preference.

While redundancy and monitoring are important, the type of battery you choose also affects your the reliability of the UPS. There are two basic types of standard batteries for the data center.

Wet cell lead acid batteries take up a lot of space, require special rooms to house them and cost three times as much to install compared to newer technologies. Upshot: 20-25 year life span for the batteries is normal. Large data centers will usually have multiple strings of this type of battery.

Valve regulated Lead Acid batteries are heavy but safer than traditional lead acid. They are a newer technology, but five-year rated cells have a realistic life of one to three years. Ten-year cells last four to seven years.

"And these only last that long if you rarely use them," McFarlane said.

Let us know what you think about the story; e-mail: Matt Stansberry, News Editor

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