An uninterruptible power supply (UPS) is a backup power source that activates when the main source fails. Although complex to create, a UPS has a very simple overall design and concept.Every UPS has power inputs (for intake of commercial power during normal operation), power outputs (to connect protected equipment), and backup batteries (to prevent interruption of power to protected gear when commercial power is lost). It also has a control system that quickly switches to backup battery power when the main source of electricity goes down.
The word "uninterruptible" means that the power supply will activate quickly enough to prevent the gear from ever losing power when the main power source goes dark. This means that a UPS system must be capable of activating backup power within 25ms of a power loss.
Redundant in nature, the UPS provides an important protective barrier against data loss and hardware damage.
In consumer applications, a UPS 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 joined computer gear.
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 most likely expected to be rare and brief, a UPS may be only backup power source at a remote site. However, at least one diesel or propane generator is also present to provide backup power.
Unfortunately, many network managers fail to properly monitor their UPS systems.
This is primarily because most moder UPS systems for use in industrial applications include a built-in web interface for performance tracking. Although this would be considered "monitoring," one vital flop prevents it from being "proper monitoring."
Using a UPS's own interface for uptime monitoring defeats the reason 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, will send alerts back to vital personnel via LAN, phone voice message, serial connection, T1, fiber, or other available transport.
In this way, organizations can track and log the voltage levels of each single battery cell, providing a good assessment of the overall health of the battery string.
Even better, RTU's will monitor much more than just UPS. Just about every piece of telecom, transport, and switching gear you have will also benefit from external monitoring.
When using RTUs to monitor a UPS, 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 urge 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 UPS 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 UPS 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.
- 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.
- Ambient temp 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.
- Overcharging, at a level of 20 amps per 100 amps of battery capacity, is also monitored carefully.
- Monitoring voltage to prevent deep discharge is perhaps the most important role of the UPS battery monitoring solution. As an example, if you discharge batteries at 44 V and they drop to 42 V, you have damaged the batteries.
Download PDF:UPS Monitoring Tutorial.