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UPS (uninterruptable power supply)

Today's power grid is still not capable of supplying continuous power without any interruptions. Sometimes power fluctuates, other times transformer blows or wire is severed. Your computer is a sensitive equipment that does not like unpredictable power input. Issues arising from peaks (when input voltage exceeds ordinary values), brownouts (when voltage drops) and blackouts or power failures (complete power interruption) could range from lost work, diminished lifetime of your power supplies to complete destruction of your hardware.

First, let us discuss total power failure. Long term interruptions can be aleviated by stand by generators, however modern computers draw so much power that most will shutdown within 0.2 seconds of power loss. You can bridge the gap of several seconds that it takes generator to go online by supplying battery backed up current. Even the cheapest UPS on the market will do (provided your draw does not exceed rating) as they are capable of providing at minimum 5 minutes of power. Situation with brownouts and peaks is not so simple as most low-end UPS machines are "offline" ups systems.

Standard offline ups is not running until after power failure occurs. UPS can react very quickly to power failure. During the fraction of second that is required to switch it on, the capacitors in your computer's power supply will maintain operational power to all its components. When UPS is in offline mode, the built in battery is charged or its charge is maintained. When power loss occurs, the built in invertor will start generating output power by drawing down from the lead acid battery. When power comes back online, UPS will monitor it for several seconds and if no further interruptions are detected, the main is let through and battery goes to charge mode.

Pros of offline UPS include low price. Many offline UPSes include surge protector, but you should carefully study the guide as generally half the sockets are only surge protected while the other half is battery backed up. It makes sense to connect your printer, for example, to surge protected outlet. You should connect your computer and your monitor to battery backed up output. Your monitor is vital and without it you will not be able to save your documents and shutdown your computer properly.

Cons of offline UPS include brief power interruption during power loss and generally poor filtering support for peaks and brownouts. All of these will shorten life of your computer's power supply. If your equipment is voltage sensitive you may need to spend more money by purchasing online UPS. Many times you will not realize that you draw more power from battery backed up sockets than your UPS can support and during brief outage is not a good time to find out. You should periodically test UPS to verify that it will perform. Naturally you should save your documents before doing so.

Scroll down for additional info labeled Online UPS and discussion on hidden cost of running UPS systems

More info: Online UPS and discussion on hidden cost of running UPS systems

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At minimum, online UPS has to have two sets of batteries. One set charging while the other set is being drained. Online UPS always runs on battery so there are no brownouts or peaks. Line noise is generally lower from online UPS than from main so again, consider for sensitive equipment. This system is always more expensive than offline UPS. You will have the peace of mind knowing that your investment is well protected against power related issues of all kinds.

When you visit store and purchase UPS, that's not the extent of expenses that you will occur. The obvious additional expense are batteries - they do go bad after a few years, although a replacement could be purchased for about $20 dollars for cheaper offline UPS systems. One hidden cost that I do not hear much about is additional power drain. The batteries must be charged and recharged constantly. They do not take much to keep charge but it all adds up over time. The efficiency is not 100% so while you can run on UPS for 5-20 minutes depending on model and drain, the equivalent power consumed to charge the batteries can easily top 1 hour at same current. All batteries loose power, fortunately in case of lead acid batteries that loss is minimal so maintenance charge is small. The UPS system has to continuously monitor power and as with your TV - if it's not unplugged, it drains power.