Uninterruptible battery backup for IBM AS/400 systems

This paper describes the architecture and implementation of a DC-Uninterruptible Power Source (DC-UPS) designed as an internal component for IBM AS/400® processor and I/O towers. This DC-UPS supports a processor or I/O tower requiring a maximum of 3100 watts of input ac line power. Unlike the large majority of AC-Uninterruptible Power Sources (AC-UPSs) found in the marketplace, which supply 50–60-Hz alternating current, the DC-UPS supplies direct current as the backup power source to the power supplies of these IBM systems. This paper addresses the way in which the IBM DC-UPS design evolved, and how the DC-UPS is less complex, more reliable, and less costly than AC-UPS designs. It also discusses some of the design considerations required to maintain and manage a large battery string in an IBM computer system.