Backup batteries have been a fact of life in intrusion, access and even video surveillance systems for quite a while. Whether in a local panel or as part of a power supply enclosure, batteries serve the function of maintaining power during a limited duration power outage. UL standards cover these — requiring four hours for access control (UL294), 12 or 24 hours for intrusion (UL 603 and UL 1076), and 24 hours for fire (UL 864 and UL 1481). If video systems are used as sensors in these systems, they may also fall under this umbrella.
Uninterruptible power supply (UPS) systems provide protection beyond batteries, supplying low voltage or line-level voltage to selected end-devices or to power supply panels themselves. “Providing clean, stable power is essential for all mission critical systems, as well as peripheral support devices,” says Bill Allen, Director of Marketing for Minuteman Power Technologies. “Since UPS (systems) are at an all-time low in terms of affordability, there’s very little reason why a security system cannot be fully protected from all power problems.”
UPS Features & Vendor Offerings
Battery back-up is improved with intelligent charging. LifeSafety Power, for example, has incorporated a feature in its power supplies that enables the charge voltage to go higher than the main supply voltage, reducing stress and heat generation on attached devices while providing optimum charge to the battery throughout the charge cycle. A “jumpstart” feature provides maximum current at the beginning of the charge cycle to get battery chemistry moving and reduce the effects of deep discharge. The company has also pioneered advanced network-based monitoring and control features in its power supplies that provide notification of power loss and other important features. This may be particularly helpful if the loss of AC power is localized.
The dividing line between when to move from batteries to UPS is a judgment call. “Both conventional battery backup and UPS systems are tools to enhance the reliability of the powered system, dependably and economically,” says Joseph Holland, VP of Engineering for LifeSafety Power. “A properly designed power supply with battery charger and monitoring will provide the most efficient and cost effective method for a dedicated specific system. A battery solution, however, cannot compare with the ability of UPS to handle the broader-based power requirements of the IT world.”
The typical UPS goes through a 3 stage (in-DC-out) voltage conversion process, where the DC section is backed up via battery. Failure of the incoming voltage is countered by the conversion of the battery-backed DC power to the required voltage output.
Altronix also offers a line of UPS systems (ReServ) — primarily oriented toward video — which offers both 24 VAC and 12 VDC output capabilities. Typical back-up times are 45 or 90 minutes, depending on battery configuration.
Panduit Corp., offers a DC UPS which accepts DC-in and provides 35 W of 24 VDC power out. Its product eliminates batteries to improve reliability. The system uses ultra capacitors — also commonly known as super capacitors — which have lower energy density but higher power density than batteries, resulting in much shorter charge/discharge cycles. The result is 6-plus minutes of backup power, enough to deal with short duration “blips”— in a package roughly 3 x 5.5 x 7 inches.
While the systems described above provide low voltage out, the more traditional UPS systems are line voltage in/line voltage out. Minuteman Power characterizes power problems and frequency of those as follows: surges (1%), blackouts (5%), spikes (6%), and sags and brownouts (88%) — a spike can be described as a wave of power via over–voltage vs. a spike which is a short duration event of several milliseconds. Many worry most about the complete loss of power, but equipment powered by AC will have varying degrees of susceptibility to abnormal voltage fluctuations, and UPS systems effectively clean this up. Minuteman’s EnterprisePlus LCD Line Interactive Uninterruptible Power Supply provides the following specifications: