Tech Tidbits, vol. 6 - UPS Battery Capacity and Aging

The function of an Uninterrupted Power Supply, or UPS, is to provide clean back-up power supply for

essential and critical systems. These systems include the general alarm, navigational,

telecommunications, power plant, station keeping capabilities, and BOP control systems, in the event

of a power failure of the primary power source(s). Accordingly, irregularities with the UPS systems

could result in system failures with devastating consequences.

On a recent assessment, WEST found the preventive maintenance program did not specify periodic

replacement of these critical batteries. Battery capacity is regulated by regulatory bodies such as ABS,

DNV, Lloyds, API, IEEE and others. These organizations require minimum times for retention of

nominal voltage after charger or line power failure. DNV, for example, specifies periodic testing to

ensure sufficient capacity is provided for 30 minutes of operation with batteries. Additionally, there

were no alarms installed to alert personnel to system failures as recommended by these standards.

UPS in a Distribution System

Best oilfield practice suggests batteries in every UPS should be regularly replaced, depending on

battery type, to ensure adequate power for backup of critical systems in case of a power loss. For gel

type batteries, commonly used offshore today, replacement should occur biannually. The particular rig

referenced above was nearing two years of age, and battery replacement had not been scheduled.

Also on the topic of batteries, all systems using batteries should include periodic replacement in their

preventative maintenance program. This is most critical in systems where such batteries provide

backup functions and dead or weak batteries cannot be identified until the system fails as a result.

Most PLCs have a Lithium battery to reload the program code from the EPROM on reinstatement of

power. However, if the battery fails, you have no program!