Once considered a pricey luxury used to protect only the most sophisticated computer systems, the uninterruptible power source (UPS) has achieved the status of workhorse guardian.
Now more affordable than ever, UPS units have become an essential piece of equipment in myriad settings, from large data centers to home entertainment systems. But nowhere is a UPS application more essential than for security. In a day and age when most products incorporate microprocessors and, therefore, require boot-up time, UPS units have become even more critical. Consider a half-second loss of power to a system could easily result in a reset time of several minutes or longer – an unacceptable episode for equipment that requires 100-percent uptime, such as surveillance cameras and access control systems.
While UPS systems are designed and specified differently depending on the manufacturer, there are some commonly accepted guidelines that, for the most part, apply to all. I’ll do my best to address the most common questions here in a question-and-answer format.
Q. What equipment should use a UPS?
A. In the event of a power sag or outage, a UPS functions to reduce the chance of equipment damage or time delay for rebooting. Any equipment that fits into this category clearly needs to be protected.
A secondary category is equipment that requires 100-percent uptime, such as surveillance cameras, access control systems and other electrical devices that cannot be manually operated during an extended power failure.
The third equipment category often receives less consideration, but can be no less vital: ensure that you have a UPS on accessory devices that will be needed during a power outage. These include rack service lights, keyboard-video-mouse (KVM) switches, cordless telephones and similar devices.
Q. How are UPS sizes determined?
A. A UPS system is sized by two determining factors: runtime and load rating. The latter figure often receives the most attention because it represents the amount of power the UPS is designed to supply. A good rule of thumb here: the UPS should provide an amount 25-percent greater than the cumulative power requirements of the attached equipment.
The significance of the runtime figure must not be misjudged. This rating determines how many minutes the UPS will continue to provide power at full load to the connected equipment. If an 800 volt-amps (VA) UPS has a runtime of 15 minutes, and a longer runtime is required, operate it at half load to almost double the runtime.
Q. How much runtime is required?
A. Most power brownouts last a few seconds or less, so a UPS with limited runtime is perfectly suitable for applications in similar periods of reduced voltage. However, the runtime on a UPS should be specified either to exceed the worst-case downtime or to allow the orderly shutdown of attached equipment.
If your facility has a generator, the UPS need only bridge the gap between the loss of utility power and the availability of generator power. In event of power loss, modern generators are able to come online in a matter of a few seconds. Older equipment can take up to 10 minutes or longer to kick in if the generator isn’t well maintained.
To be most prudent, figure 20 minutes of runtime at a minimum – no matter how modern the generator. Thirty minutes is good for older generators. And if the unit can’t be brought online in half an hour, chances are your system will be shutting down.
Note that too much runtime isn’t practical. It will increase the cost of the UPS system exponentially, add size and heat, and won’t likely give you a tangible benefit. Why? Because most power drops are extremely short in duration. There will be more batteries to test and maintain, and the maintenance expense will be significantly higher than a UPS that has been sized correctly.
Q. My equipment says watts, but my UPS says VA. Are they the same?
A. No, and this is a major issue when deploying a UPS. To calculate the wattage (W) rating of a UPS, manufacturers multiply the VA rating with a “power factor” or the actual amount of power drawn by the equipment. So, a 1,000VA UPS specified with a factor of .8 will deliver 800W, while a similarly specified UPS with a power factor of 1 will deliver 1,000W, both at the rated runtime.
Since UPS factors can range from .66 to 1 (modern computers can be as high as 0.97), disregard the VA rating and focus on watts. If you can’t find the wattage rating, contact the manufacturer or move on to another unit.
For the complete version of this story, see the November issue of Security Sales & Integration magazine.
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