Since much of today’s test equipment is computer-based, PC and network power-outage survivability is a major concern. Some of your equipment may require protection from power outages some of the time, such as whenever it is in use. But all your equipment needs surge protection—to prevent transient-induced damage—all of the time, whether it is in operation or not.
Fortunately, surge suppression is performed by passive components which are ready and able to carry out their intended function at any time. Batteries, the power source of the uninterruptible power supplies (UPSs) during a power outage, can fulfill their task only if they contain an adequate charge.
The size of the battery and its charging state determine how long your sensitive equipment, such as a PC or a server, can remain operational in a power outage. Smaller batteries are preferable over larger ones for space, weight and cost reasons, but are they adequate for your application?
UPS designers have addressed this question and proper charge-maintenance and battery-life-expectancy issues in a number of ways. To fulfill the demands for broader but more compact surge protection, designers also have devised novel combined power, network and telecom line-protection equipment.
Batteries—The Power Source for Your UPS
Size Considerations
Comparing physical dimensions of present UPSs and batteries with those used several years ago, a distinct decrease in size is discernible. The size reduction is a result of two factors: loads provide more computational power per watt consumed, and smaller batteries are being used.
“With batteries getting smaller and lighter, the UPS design is also getting smaller and lighter,” said Ken Krause, national sales manager at Controlled Power. “This makes it easier to place UPSs in tight spaces, less obtrusive to the PC user. From a manufacturer’s perspective, the lighter weight makes the UPS simpler to package and less expensive to ship, which reduces the cost of the UPS.
“On the other hand, the smaller batteries affect UPS performance,” Mr. Krause continued. “If smaller batteries must provide the needed power, they must support rapid discharge. This means that all stored energy may be dissipated in a short time, significantly reducing the run time of the UPS in the event of an outage.”
How long can a battery provide a certain amount of power? This is a key question that must be answered before UPSs or batteries are selected.
“Batteries have different measures of storage capacity,” said Fred Stich, chief
technical officer of Best Power. “Generally, these are distinguished by the time over which a battery is discharged or by the type of discharge the battery must support.
“For example, two totally different measures could be the 20-hour constant- current discharge (the normal amp-hour rating) and a 15-minute constant-demand power discharge. The latter is the more important for typical UPS applications and is the one which has benefited most from recent lead-acid battery developments. These improvements allow large amounts of energy to be extracted over relatively short times,” Mr. Stich concluded.
Using Battery Power Judiciously
Most off-line and line-interactive UPSs contain voltage regulator circuitry that accepts undervoltage or overvoltage conditions at its input and provides a constant voltage at its output. When the line voltage drops below the limit the regulator can handle, the UPS switches to its battery-powered operating mode. For information on topologies and operating principles of UPS, see References 1 and 2.
Power outages often are preceded by a sagging line voltage or extended brownouts. If the regulator can tolerate only a minimal decrease in line voltage, the UPS may switch to battery power prematurely and use up the stored battery charge before the actual outage occurs—obviously an undesirable situation.
“In an off-line UPS, a key performance measure is the range of power the UPS will accept before switching to battery backup,” said Tom Pfendler, market manager at Liebert. “The wider the range, the less the drain on the battery and the more backup time you will have when the power is off. Also, the more times the UPS switches to battery backup, the shorter the battery life.”
“A line-interactive UPS innately includes voltage boost circuitry and accepts a wide range of input voltages,” Mr. Pfendler continued. “Look for UPSs that provide boost from at least 25% below standard voltage before switching to battery backup. Also, find out how much input overvoltage the unit will tolerate. The wider the range, the more protection you will have.”
Some UPSs include special circuitry to extend the acceptable input voltage range. DELTEC, for instance, uses a buck and double-boost voltage regulator that corrects for input voltage variations from as low as -35% to as high as +20% of nominal voltage. Controlled Power has a Fuzzy Ranging™ control system that accepts voltages from -40% to +10% of nominal before switching to the battery. The range you need depends on your local power-utility environment.
Prolonging Up-Time Through Load-Control
A question often asked is: How long should a UPS power the load after an outage has occurred? The answer is that, as a minimum, enough up-time must be available to achieve an orderly shutdown so that there is no loss of data. This shutdown may be performed by a person alerted by a visual or audible alarm originating from the UPS or a network coordinator, or unattended via power-management software.
While five minutes may be more than adequate to accomplish such a shutdown, in actual practice, much more time is desired. “Because a power outage is frequently followed by additional outages, we typically recommend 15 to 20 minutes of run time to ensure a safe shutdown of computer equipment and ample time for additional shutdowns if necessary,” advised Tim Bailey, marketing manager at International Power.
In a situation where one piece of equipment is key to maintaining major functions, the most critical equipment should receive power longer than the less significant power consumers. Selective parceling of backup power may be accomplished in many ways. In its simplest form, the network manager may remotely control the on/off state of less essential devices. This can be accomplished by controlling UPS power distribution by remotely activating network peripheral switching devices such as the Tripp Lite SmartSocket™ UPS outlet controllers.
A similar but highly integrated solution is provided by programmable load segmenting, as implemented by American Power Conversion (APC) in the Matrix-UPS™ product and by DELTEC with the Power Extend Technology™. Figure 1 shows a typical example of how this technique provides longer uptime for critical equipment in a network.
Load 1 in Figure 1 is a UNIX file server with a 19″ monitor, consuming 500 VA and load 2 is a workstation with a 12″ monitor consuming 200 VA. Both are connected to a PowerRite Max UPS. By immediately proceeding with a controlled shutdown of the workstation, almost twice as much run time is provided for the server.
Charging Choices and Battery-Life Expectancy
Most UPSs keep their batteries charged by applying a trickle charge. In this process, the battery is connecting to a constant voltage source via a current limiting resistor.
After a power outage has occurred, the battery is partially or fully discharged. Since additional outages may occur, it is desirable to recharge the battery as quickly as possible. In this case, trickle charging is not appropriate since it would be too time- consuming. To replenish the charge quickly, a relatively high constant current is applied.
The more current that is forced into the battery, the faster it will be fully charged—unless it becomes damaged in the process. Clearly, a balance between desired recharging time and non-life-shortening current levels must be struck.
Battery life may also be adversely affected by excessive trickle-current levels or charging time. To address these issues, several manufacturers are carefully programming all battery-charging functions.
For instance, a patented three-stage battery-charging technique employed by DELTEC applies a moderate-level constant-current charge for three hours, followed by a constant-voltage trickle charge for up to 48 hours. When the battery is fully charged, all charging is discontinued.
The charger is turned on again to replenish battery charge due to use or natural decay during extended periods of nonuse. Employing this three-step procedure extends battery life by a factor of two, according to DELTEC.
All batteries will eventually fail. To ensure that backup power is available when needed, UPS users require advance warning when batteries approach the end of their useful life. To provide this information, most UPSs are designed to perform regularly scheduled battery-quality checks, some with a higher predictive success rate than others.
Several UPS manufacturers combine charge-management, failure-prediction and available-run time reporting circuitry. These functions may reside in the UPS or be located at the battery. The APC SmartCell and SmartCellXR batteries, for instance, contain a small microprocessor which reports if battery charge is low and whether a battery can accept or hold a charge.
The Expanded Role of Surge Suppressors
While the prime function of the UPS is data-loss prevention, surge suppressors prevent equipment damage, potentially caused by lightning or other transient events. While peripheral equipment, such as printers, scanners or powered sound systems connected to your computer, do not need to be fed from a UPS, they certainly should be protected from transients through the use of surge-suppressing equipment.
Most UPSs contain built-in surge-suppression circuitry to protect your equipment from transient events occurring on your power lines. But this alone may be inadequate, and transients on network and telephone lines can also inflict serious damage.
Serial RS-232 interface ports are particularly susceptible to transient-related damage, since they use the computer chassis ground as a signal return. APC recommends that you protect both ends of a serial RS-232 cable if it is longer than 5’ and protect every 9-pin or 25-pin port of your computer, modem, printer or plotter. Also each network interface card should be protected, since network interconnections can be especially vulnerable if cable shields are inadvertently grounded at each end.
Communications line surge suppressors, with and without EMI/RFI protection features, are now available from many UPS suppliers. To provide the utmost in compactness and assure single-point grounding, several companies have introduced all-inclusive protection units for PCs and workstations.
Such units have surge protectors for common communications and network ports. Some may include a dual set of surge-protected outlets, half of which obtain their power from a UPS. Examples of these include the Tripp Lite TouchMaster UPS which fits under a typical PC, Controlled Power’s LTX uninterruptible power center, and APC’s Back-UPS® Office™ unit.
Configuration Guidance Via Internet
Since choices abound, all companies whose products are described in the product section of this article can provide you with the data you need to select the UPS or surge suppressor suited for your application. Valuable information may also be downloaded over the Internet.
APC offers a free interactive power guide, called the Desktop Protection Planner, available on floppy disk or from http://www.apcc.com. Exide Electronics supplies an interactive configuration tool via http://www.exide.com, entitled “Build Your Own Power Solution.” The MINUTEMAN web page “The Power Line” (http://www.minuteman-ups.com) provides tutorial information, specifications and a quiz with answers to help you find the appropriate MINUTEMAN UPS for your application.
Liebert offers PlanUPS™, a Windows-based program designed to help you select the proper protection products, complete with model numbers and pricing information. PlanUPS may be downloaded by accessing http://www.liebert.com. Best Power makes power management software for its equipment available free from http://www.bestpower.com. More UPS-related information may be found at http://www.tripplite.com.
References
1. The Power Protection Handbook, American Power Conversion.
2. Jacob, G., “Clean Power Essential to Today’s PC Systems,” EE Evaluation Engineering, December 1995, pp. 32-39.
Power Conditioning Products
UPS Includes Extensive
Surge-Suppression Capabilities
The Intelligent UPS (I-UPS) Uninterruptible Power Supplies are offered in ratings extending from 450 VA to 2,400 VA. The units handle brownouts (as low as 85 V) without consuming battery power and provide sine wave output with <3% THD. In case of power outages, the transfer time is 2 to 3.5 ms and the battery backup time is five to 24 minutes. The I-UPS includes a separate dedicated surge-suppression board that features a single-pulse surge energy absorption of 1,810 joules. From $395. International Power Technologies, (800) 944-0356.
Intelligent UPS Includes Power
Management Software on CD ROM
The SmartPro™ Net line-interactive UPSs are now offered with PowerAlert Plus™ network management software on CD ROM. The software and interconnection facilities support Novell, Windows 95/Windows/Windows NT, OS/2, UNIX, HP-UX and HP Openview; and include Tripp Lite’s Novell SNMP Agent that accommodates Simple Network Management Protocol (SNMP) without adapters. The SmartPro Net protects against power outages, accommodates input voltages from 87 V to 140 V, and provides spike, surge and line noise protection. Models range from 280 VA to 5 kVA. From $310. Tripp Lite, (312) 755-5400.
Compact Rack-Mounted UPS
Developed for OEM Applications
The compact NetUPS® Rack-Mount 700-VA unit developed for OEM applications is suited for integration into rack-mount and stackable internetworking systems. Its dimensions are 2.6″ high (1.5 rack units) x 17.5″ wide x 14.5″ deep. The NetUPS protects servers, routers and hubs from power surges, brownouts and utility failures. Surge suppression and line filtering protect network components from transient power disturbances caused by lightning and common utility perturbations. Exide Electronics, (800) 554-3448.
Single Unit Addresses Power,
Data, Telephone Line Problems
The LTX Uninterruptible Power Center (UPC) Series is designed to protect equipment not only from power outages but also from potential problems due to disturbances caused by power line, telco and data-line anomalies. Three models are offered in the Series LTX UPC enclosure, ranging from 400 VA to 850 VA. A patented fuzzy-ranging battery management system extends the life of the batteries. The DATAGUARD automatic unattended shutdown feature for computer systems is optional. From $850. Controlled Power, (800) 521-4792.
Full-Featured UPS Now
Available for Smaller Loads
Available in 250-VA, 400-VA and 600-VA versions, PowerSure protects sensitive electronics against blackouts and brownouts. The units accept inputs from 95 V to 132 V, meet UL 1449 standards for surge protection and are FCC Class B rated for low / EMI/RFI emissions. In power outages, five to 10 minutes of battery time is provided and a two-minute low-battery alarm warns that it’s time to save and shut down applications. Communications with auto-shutdown via SiteNet 1 is optional. 250 VA: $173; 400 VA: $258; 600 VA: $431. Liebert, (614) 888-0246.
Power-Management Software
Extends Battery Run time
PowerRite Max UPSs with 1,000-VA and 1,500-VA ratings now come bundled with a Windows 95 plug-and-play driver and the company’s LanSafe and FailSafe power-management software. LanSafe and FailSafe use proprietary Precision Power Control technology to save battery backup time by scheduling less important equipment to shut down first, allowing more battery run time for critical devices. PowerRite Max also features advanced battery management hot-swappable batteries, network/modem surge protection, proprietary buck/double-boost voltage regulation and SNMP capabilities. 400 VA: $339; 700 VA: $419; 1,000 VA: $649; 1,500 VA $819. DELTEC, (800) DELTEC-1.
UPS Includes Surge Protection
For Phone, Network Data Lines
The Back-UPS Office™ multipath power device prevents hardware damage caused by surges and data loss from brownouts and blackouts. It features multioutlet AC surge protection, phone-line protection for Internet users, network data-line protection for corporate workstations and battery backup. Three outlets provide battery-backed power for data protection of critical components. Three additional outlets are dedicated to peripherals. Back-UPS Office furnishes seven to 13 minutes of battery backup and includes high-performance multistage surge suppression and EMI/RFI filtering. $179. American Power Conversion, (401) 789-5735.
Enhanced UPSs Offer Power
Management and Protection
The new generation of Fortress® UPSs provides more power management and protection in network computing environments. The units deliver a no-break sine wave output and correct voltage sags and overvoltages with the PowerSteady™ regulation feature which permits ride-through of chronic sags without using the battery. Added features include PowerSteady™ voltage regulation, a simple-to-use hot-swap battery capability, Windows 95 plug-and-play compatibility and the bundled CheckUPS II Suite power management software compatible with Novell, UNIX, Windows 3.1/95/NT, DOS and OS/2. 520 VA: $509; 720 VA: $549; l,020 VA: $799; 1,420 VA: $999. Best Power, (800) 356-5794.
UPS Includes Modem/Fax
Network Surge Protection
The Pro Series of uninterruptible power supplies, available in ratings from 280 to 1,400 VA, provides protection from sags, surges, spikes and blackouts. Line-interactive boost/buck capabilities extend the input voltage range from 88 V to 141 V without going into the battery mode. Microprocessor control provides automatic battery management to oversee battery recharge functions. Bidirectional communications facilities interface with the company’s LANMASTER power management software. Surge protection for data and modem lines is built-in. From $139. MINUTEMAN, 800-238-7272.
Rugged UPS Accepts
Range of Power Sources
The GUPS™ Global Uninterruptible Power Supply Systems are rugged and suited for mobile applications. The 1,250 VA GUPS offers power-factor correction and accepts AC input voltages from 80 V to 280 V at frequencies of 45 Hz to 450 Hz. It also operates from 28 VDC. The input circuitry automatically reconfigures the GUPS in conformance with applied power. Low output impedance helps drive nonlinear loads.
The units meet vibration and shock requirements as specified by MIL-STD-810E.
1,250 VA: from $4,840; 2,400 VA: $8,760. Elgar, (800) 733-5427.
Copyright 1996 Nelson Publishing Inc.
December 1996