Greening the data center : The DC power battery string ….


In previous posts, I’ve discussed the green usage of DC power in the data center, tips on how to choose your DC power plant, and tips for insuring that your data center DC power plant is as green as it can be. Today I’m going to talk about the care and feeding of the battery string.

The battery string is the only consumable part of the data center DC power plant and an expensive part also. Choosing the optimal batteries and maintaining them properly provides maximum performance and maximum lifespan.

For battery choice, sealed, deep cycle batteries that are equipped with plates made with low sulfur lead will usually prove the best. These type of batteries require no additional water, have no chance of producing flammable hydrogen gas, are built strongly enough to withstand hard usage, and are less susceptible to failure from sulfation.

The first item for batteries is to insure good solid connections. For safety purposes, disconnect the string from the power plant before working with the connections. When working on the inter-battery connections, make sure to use insulated tools. Shorting battery connections can result in dangerous arcs, damaged tools, and personal injury.

Clean and tighten all battery connections, also coat connections with a corrosion preventer such as petroleum jelly. This will insure the best life of the connections and the least power loss in the connections.

The second item is to use the proper float voltage. The power plant should be set just slightly above the voltage of the fully charged battery string. Most battery cells run from 2.1V to 2.2V so the float voltage should be cell voltage X 24 cells + .2V. Most of my battery strings float at 52.2V (refer to the battery manufacturer for the cell voltage).

Next, periodically exercise the batteries by switching the load to them. This prevents the water and acid in the battery from separating and also helps prevent coating of the plates with sulfur.

The next item, is testing battery symmetry. Symmetry is tested by measuring the voltage on each battery in the string under load. Any batteries that measure an even multiple of 2.1 to 2.2V low should be replace for failed cells. Any batteries with odd low voltages should be equalized and then replaced if they still measure low.

Equalization applies a higher voltage than the float voltage for a short period of time (usually 56V vs 52V). This can sometimes straighten out underperforming batteries.

Finally, make sure the batteries are operating in a cool, even temperature. Nothing degrades a battery faster than operating in high temperatures.

Take care of your batteries, give them the right operating environment and a little TLC, and your green data center DC power plant will give you the best results possible!

Vern, SwiftWater Telecom
data center, web hosting, Internet engineering

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