Uninterruptible Power Supply Monitoring

An uninterruptible power supply (UPS) is a backup power source that activates automatically when the primary source (typically commercial AC) fails. Although technically complex, a UPS has a very simple overall design. Every uninterruptible power supply has power inputs (for intake of commercial power during normal operation), power outputs (to connect protected equipment), backup batteries (to prevent interruption of power to protected equipment when commercial power is lost), and a control system that quickly switches to backup battery power when the main source of electricity becomes unavailable.

The word "uninterruptible" indicates that the power supply will activate quickly enough to prevent the connected equipment from ever losing power when the primary power source goes dark. This typically means that a UPS system must be capable of automatically activating backup power within 25ms of a power loss.

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Uninterruptible Power Supply (UPS) Monitoring Tutorial

An uninterruptible power supply, which by its very nature is redundant, provides an important protective barrier against data loss and expensive hardware damage.

In consumer applications, an uninterruptible power supply may only have enough battery reserve to last for a few minutes. The intent of such a short backup power supply is only to allow safe shutdown of connected computer equipment.

In a telecom or data center environment, however, the batteries of a UPS may last for several hours or more. If commercial power failures are generally expected to be rare and brief, an uninterruptible power supply may be only backup power source at a remote site. Generally, however, at least one diesel or propane generator is also present to provide backup power.

In this diagram, a BVM ("Battery Voltage Monitor") 48 collects voltage levels from 24 UPS battery cells and uses LANs to report SNMP traps and host its own web browser interface for monitoring and configuration...

Unfortunately, many network managers fail to properly monitor their uninterruptible power supply systems.

This is primarily because most modern UPS systems for use in industrial applications include a built-in web interface for performance tracking. Although this obviously would be considered "monitoring," one critical flop prevents it from being "proper monitoring."

Using an uninterruptible power supply's own interface for performance and uptime monitoring defeats the purpose of such monitoring. If the UPS fails, so too will the monitoring interface that you have relied on.

Instead, the industry best practice is to deploy relatively low-cost external monitoring devices. Small monitoring devices (1 RU or less) are available to collect important status information from virtually any UPS backup system.

These monitoring devices, commonly known as "RTUs" (Remote Terminal Units or Remote Telemetry Units), will send alerts back to critical personnel via LAN, phone voice message, serial connection, T1, fiber, or other available transport.

In this way, organizations can continuously track and log the voltage levels of each individual battery cell, providing an excellent assessment of the overall health of the battery string.

Even better, RTU's will monitor much more than just uninterruptible power supplies. Just about every piece of telecom, transport, and switching gear you have will also benefit from external monitoring.

When using RTU's to monitor an uninterruptible power supply, it's also very important to remember that an RTU also needs electric power to report alarms back to you. Because your monitoring system should always be the last thing to fail, you should resist the temptation to power your RTU using your UPS system. If you do this and the UPS fails, you will have no way of knowing until the site goes completely dark.

A good RTU will contain its own internal uninterruptible power supply with backup batteries large enough to continue operation for at least several hours after a power failure. Some of the top-quality RTU's will last for up to 10 hours.

Real-World Examples of UPS Monitoring
DPS Telecom has seen clients roll out uninterruptible power supply monitoring systems at dozens of sites to protect the battery cells there from expensive damage. The battery monitoring systems that they deploy cover both VRLA ("Valve-Regulated Lead-Acid") batteries and flooded batteries.

These clients monitor several aspects of their UPS batteries:

1. Float voltage must maintain a steady level of 54 volts. If this level rises too high, the battery cell will dry out. If it falls too low, sulfate deposits will build and the cells will eventually short out.
2. Ambient temperature at the site must remain near the ideal level of 77°F. a higher temperature degrades the cell, and a lower temperature decreases the capacity of the battery cells.
3. Overcharging, at a level of 20 amps per 100 amps of battery capacity, is also monitored carefully.
4. Monitoring voltage to prevent deep discharge is perhaps the most important role of the uninterruptible power source battery monitoring solution. As an example, if you discharge batteries at 44 V and they drop to 42 V, you have damaged the batteries.

Related Products:
UPS Battery Voltage Monitoring Device
Central Monitoring Master Station

Related Topics:
UPS Power Supply
UPS Battery Backup