Choosing The Right Size UPS
Battery backup devices, or Uninterruptible Power Supplies, are growing more common as users realize the benefits of protecting their systems and data from all types of power problems. However, when purchasing a UPS many users are confused by the multitude of choices available.
Levels of Protection
For those of you unfamiliar with UPS devices, a UPS has a large battery that turns on whenever a power fluctuation occurs. A standard surge protector, by contrast, only protects against lightning strikes or other power surges, and does not provide protection against blackouts or voltage fluctuations.
A UPS can sense any change in voltage and switch to its built-in battery. In fact, many units always leave the battery in use, to avoid even a microsecond's delay while switching. The battery is then continuously charged from the wall plug. UPSs also provide surge protection, replacing the need for separate surge protectors.
This allows a UPS to protect against all of the above conditions, at least until its battery runs out.
Battery Life
The reason so many different UPS models exist is mostly the difference in batteries. A larger battery will provide more power, and allow connected devices to run longer. For example, APC has a small, sub-$100 model which allows a standard PC to run for about five minutes on battery power. This provides enough time to save your files and gracefully shut down. A UPS with more capacity would allow the same PC to run longer, or perhaps power two PCs for the same amount of time.
What Not to Connect to a UPS
Never connect a laser printer to a small UPS. When the fuser element heats up, a printer draws a large amount of current, more than a small or even medium UPS can provide. If this happens, you will trip the circuit breaker in the UPS. If you would like your new laser printer to be protected, only the larger UPS models will be able to provide the power required.
Determine Your Requirements
The two most important considerations are the amount of power required, and the runtime, or battery life, you wish to have.
The power requirements are dictated by the number of devices connected to the UPS, and the power each requires. Almost any UPS can handle a standard PC and monitor. For multiple PCs, or a phone system, you may need a larger unit. Every device will have a power requirement indicated on its nameplate. This number is usually far higher than what the device typically draws, but if you add the wattage requirements of all your devices, that will give you some idea of a minimum UPS size.
If your home or office regularly has power fluctuations or outages, select a UPS that outlasts the majority of them. Your desired runtime may be anywhere from minutes to hours. For example, if your building has a generator which takes a few minutes to turn on, you only need a small UPS. For long outages, of course, the PCs and UPSs should be shut down to avoid discharging the battery unnecessarily, although huge UPSs are available that can last days at a time.
April 2000
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