3 Approaches to Monitoring UPS Batteries – and Preventing Failures

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Companies count on their UPSs to provide clean, reliable power in their data centers and for critical equipment – they are often the last line of defense in the event of a utility power failure or other power disruption. It stands to reason, then, that companies would want to know if their UPSs are in danger of failing.

Accomplishing that requires monitoring UPS batteries, which are the least reliable component of a UPS. As any automobile owner knows, batteries have a way of failing – often with little to no warning. But in a UPS the situation is even worse because a failing battery puts additional strain on all the other batteries in the string. The failing battery will draw power from the other batteries, decreasing their life expectancy.

The life expectancy of UPS batteries can be influenced by many parameters such as:

• Room temperature
• Charge voltage and charge current
• Overcharging
• Frequent discharge cycles
• Loose connections
• Strained battery terminals

It’s surprising to me, then, that a significant number of companies fail to monitor their UPS batteries at all or believe that monitoring at the battery string level is sufficient. It is not: batteries must be monitored at the individual cell level.

Failing to monitor at the cell level leaves companies completely in the dark should a battery begin to fail and, once that happens, it won’t be long before it takes all the other batteries in the string down with it. This type of neglect is costing companies money, because all those batteries have to be replaced prematurely.

It doesn’t have to be that way. Companies have three options for monitoring their UPS batteries. Let’s go through them in order of effectiveness.

First is to have manual battery measurements performed by field service personnel during scheduled UPS or battery maintenance visits, typically annually, semi-annually or quarterly. The technician should measure float, charge and discharge voltages for each battery as well as for the whole string, the internal resistance of each battery, the charge and discharge currents for the whole string, and the ambient and individual battery temperatures. The idea is to identify any failed batteries or those that are near their failure point.

While this type of checkup is certainly better than doing nothing, it is completely reactive; most of the time, you only learn of problems after the fact, when a failed or failing battery has already started to put additional strain on the entire battery string.

A second option is to have a battery monitoring system connected to each battery cell, to provide daily automated performance measurements. Although there are many battery monitoring systems available on the market today, the number of battery parameters they monitor can vary significantly from one system to another.

A good battery monitoring system will monitor the battery parameters that IEEE 1491 recommends be measured. The 17 criteria it outlines include:

• String and cell float voltages, string and cell charge voltages, string and cell discharge voltages, AC ripple voltage
• String charge current, string discharge current, AC ripple current
• Ambient and cell temperatures
• Cell internal resistance
• Cycles

With such a system, users can set thresholds so they get alerted when a battery is about to fail.

While this is clearly a step up from the scheduled maintenance in that the alerts are more timely, they are still reactive – you only get an alert after a problem crops up.

A third, more effective way to monitor UPS batteries is to use a battery monitoring system as described above, but, in addition, to store and analyze the data it collects. Applying analytics to the data enables you to identify trends, including when a battery is on a downward spiral – but months before it is in danger of failing. You can determine when a battery is getting sick, so to speak, and replace it before it infects all the other batteries in the string.

Such a system could be integrated with a data center infrastructure management (DCIM) tool to provide a comprehensive, proactive monitoring approach. All the different parameters of the entire critical power system are now gathered and accessible in one location: the DCIM tool. That helps improve overall management and maintenance of the entire critical power system, and ultimately improves its performance.

Relatively few companies implement such a system today because it is a fairly new approach. But it can be accomplished. Using the Schneider Electric Battery Manager solution along with the StruxureWare for Data Centers DCIM offering is one effective approach that will extend the life of your UPS batteries, ensuring they are fully charged and ready when needed. That will increase the performance and availability of your entire critical power system.

Although it’s best to implement such an approach right from the beginning, a battery monitoring system can also be installed into existing critical power system battery installations. In other words, it’s not too late.

To learn more about how UPS batteries work and what makes an effective UPS design, check out our free white paper, “Design and Specification for Safe and Reliable Battery Systems for Large UPS.”