Dealing with Redundancy
There are three ways of dealing with the potential for battery failure in data centers (and any other operation that needs an assured supply). Redundancy, planned maintenance and monitoring.
Redundancy in a system with 240 single points of failure isn't a cheap option, you can't switch out a failed cell or failed battery quick enough when the utility company supply fails; to have an N+1 system you need a complete set of batteries in parallel with the first, and a second UPS. Then how are you going to calculate the risk of a failure somewhere in that second, parallel string?
Many data centers rely on planned maintenance and asset management. Planned maintenance usually takes the form of manually testing eachToshiba pa3356u-3brs Battery,Toshiba pa3285u-3brs Battery every quarter and replacing any whose performance is significantly below the rest. The asset management part is simply talking to the supplier about the batteries, the operating conditions, how often the UPS has called on them, then taking an educated guess on when is good time to replace them all. Batteries can fail suddenly, even one day after a quarterly test you cannot be sure they are all working properly. Increasing the testing frequency might help a little but it's a time consuming job (therefore expensive) and the testing current fed into the batteries to carry out the tests can actually have the effect of reducing their life. Asset management isn't optimal either; in order to reduce the likelihood of failure, most operations will err on the side of caution and replace costly batteries that could have remained in place a lot longer.
Predicting Failure
Stationary fixed battery monitoring systems carry out much more frequent checking, often checking more parameters than a technician with a hand-held monitor. Crucially they generate enough data to show trends in performance enabling data center staff to predict when a battery will fail and arrange to replace it in time. Using data collected on an entire string of batteries over an extended period, managers are able to make a rational decision about asset management, leaving a string in place as long as it remains economic to do so, but not so long that replacing individual batteries becomes a weekly event.
Alber and Btech are battery monitoring system providers who have been in this market for many years. Alber's system is built around a central device that is connected to the battery stack/cabinet with a custom-made wiring harness. Btech's is somewhat similar, but their latest models are more modular in design.
Cellwatch, IntelliBatt and Powershield all take a more modular approach with small data collection modules (DCM) on or near each battery. A Cellwatch DCM has seven colour-coded connections and is typically used to monitor four batteries. Each Powershield module monitors two batteries. Intellibatt has taken this approach even further and provides individual modules for each battery.
Obviously the first two require fewer modules, but the cost savings are not great since each module is more complex and therefore more expensive and the connections are more complicated. Intellibatt modules have two wires, coded red and black, to connect to the positive and negative terminals on the battery. In most cases data centers are able to fit their own Intellibatt system to an existing battery stack. Modules are 'daisy chained' with CAT5 cables to a data collection server which maybe in the battery rack, or a standard server rack elsewhere in the building.
Cellwatch and Powershield systems are able to take measurements on every Sony vgp-bps2 Battery,Sony vgp-bps2b Batteries every day, Intellibat up to four times per day. This high frequency of testing is made possible by improved digital processing techniques which enable ohmic measurement of each battery with much reduced current, therefore having little or no impact on battery life. Alber's system uses much higher test current and only performs tests once per month, Btech's system uses a lower current and tests weekly. Using the Data
Collecting data is pointless unless you have a method of using it. Collecting data daily, then checking it once a quarter, is no better than the old quarterly inspection regime. Of course no-one wants to wade through performance stats on dozens of batteries everyday. It makes much more sense to use some basic data processing software on the server to graph performance and show trends.
Even then, someone has to look at it, and technicians with a hundred of other tasks might easily overlook something so routine and not immediately critical. To counter this, DPMC offers a remote monitoring service. Its server is able to collect data not only from Intellibatt but from all the other major systems and relay it to its offices in California. Once there it is continuously monitored to detect errors and once a week a trending report is forwarded to the data center management team. DPMC currently monitors more than a million batteries world wide.
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