We all know that a UPS (uninterruptible power supply) is a device that keeps your equipment running for a short time when the primary power source has been lost. What may not be known is that there are a variety of other problems that a good UPS may solve, and a variety of UPS types to choose from.
A UPS may have one or a series of batteries that keep the power flowing even through a blackout. It can also provide protection against surges, spikes, sags, and line noise. A UPS can be more than just a safety net: it can regulate the power that comes from your wall socket. The UPS can ensure all your 240-volt power devices always receive clean and smooth power.
Most UPSes ship with software that will let system administrators monitor the status of the UPS from a remote location via a network node or Web. Some software can also notify users when there is a problem. If the power does not come back up before the UPS is depleted, the software can initiate a system shutdown.
The capacity of a UPS can be measured in power (measured in volt-amperes or VA) and energy (measured in watt-hours). Power determines how much equipment the UPS can operate, and energy determines how long the UPS can operate the equipment. All the UPSes in this roundup use some sort of sealed lead acid battery. These batteries’ rated lifetime is three to six years, and as they age, runtime also gradually declines.
Software plays an important role in shutting down your equipment. UPS software works by polling the UPS then posting all of its operating parameters such as battery capacity, input voltage, output voltage, and battery voltage. Some software will let you schedule a system shutdown, graph any power problems, and schedule events and create multiple logs. Information is relayed between the UPS and the computer through an RS-232C serial port or network connection.
Power Problems: Cause & Effects
- Spike: Also referred to as an impulse, a spike is an instantaneous, dramatic increase in voltage. Akin to the force of a tidal wave, a spike can enter electronic equipment through AC, network, serial, or phone lines and damage or completely destroy components.
Spikes are typically caused by a nearby lightning strike. Spikes can also occur when utility power comes back on line after, for example, having been knocked out by a storm or a car accident.
Catastrophic damage to hardware can occur and data will often be lost.
- Surge: A surge is a short-term increase in voltage, typically lasting at least 1/120 of a second.
Surges result from the presence of high-powered electrical motors, such as air conditioners, and household appliances in the vicinity. When this equipment is switched off, the extra voltage is dissipated through the power line.
Computers and similar sensitive electronic devices are designed to receive power within a certain voltage range. Anything outside of expected peak and RMS (considered the average voltage) levels will stress delicate components and cause premature failure.
- Sag: Also known as brownouts, sags are low mains voltages, which can last from 20 milliseconds to several hours. They can sometimes be seen as a dimming of lights. This is the most common power problem, accounting for 87 percent of all power disturbances according to a study by Bell Labs.
Sags are lower-than-normal voltage from the local substation, often during particularly hot or cold weather, and are usually caused by the start-up power demands of many electrical devices (including motors, compressors, elevators, shop tools, etc.)
A sag can starve a computer of the power it needs to function, and cause frozen systems and unexpected system crashes which both result in lost or corrupted data. Sags also reduce the efficiency and life span of electrical equipment, particularly motors.
- Blackout: Blackouts are total loss of power for a period between 20 milliseconds and many hours.
Blackouts are caused by excessive demand on power, or by storms, car accidents, backhoes, earthquakes, and other catastrophes. Loss of power within buildings can be due to overloads or faults blowing fuses or activating circuit breakers. A blackout results in loss of data in RAM or cache, possible loss of File Allocation Table (FAT) which can result in total loss of data stored on drive.
- Noise: More technically referred to as Electro-Magnetic Interference (EMI) and Radio Frequency Interference (RFI), electrical noise disrupts the smooth sine wave one expects from utility power.
Electrical noise is caused by many factors and phenomena, including lightning, load switching, generators, radio transmitters, and industrial equipment. It may be intermittent or chronic. Noise can introduce glitches and errors into executable programs and data files.
Battery Life
Many vendors give a fairly broad rating of battery life, (generally three to six years) which seems like a fairly large window until you consider the effects the environment can have on batteries.
Ideally, batteries should be run at 25Ã,°C to give greatest battery life. There are a number of formulae that attempt to calculate the effect of temperature on batteries. One such formula says that every 8.3Ã,°C above 25Ã,°C will reduce the battery life by 50 percent. Another is that for every 5Ã,°C above 25Ã,°C battery life decreases by 1 year.
Both of these formulae are quite similar, and clearly reflect the need for adequate cooling around your UPS, especially when they are mounted in a rack. For example, in some of our testing of last month’s 1RU Web servers, the systems reached temperatures of 50Ã,°C, which is well outside the operating conditions of these UPSes.
