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Name: tommie
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993

How exactly do UPS (Uninterruptable Power Supplies) work? Surely one cannot "store" AC like one would DC.

You are right. You cannot store AC the way you store DC. But the UPS stores the AC in the form of DC. It rectifies the AC to get DC, and stores this in a battery. Then when the UPS is needed (the AC source has failed), the DC from the battery in converted back to AC in a device known as an invertor. The bigger the battery, the longer the UPS can supply power.


UPS's generally operate in the following manner: The most efficient way (and the most fail safe) is to simply use the AC power to charge a battery. This is done by rectifying the AC and filtering and regulating to a DC voltage. The battery is then used to power the computer by the use of a DC-AC invertor that synthesizes the AC through the use of some fairly common and simple analog circuitry and a set of power transistors. That is the truly UPS systems. Other systems are simply systems with a large transformer with a large amount of iron in the core. While these are not uninterruptable, they do help filter out some of the "power glitches" that come through the line, by creating a large field in the transformer that takes a relatively long time to break when the current disappears. These, however, are not true UPS's and should not be used as one. (By the way -- instead of batteries, some UPS's now use large capacitors to store the power. These are not as long lasting as batteries yet, but they are getting much better, so look for some big advancements soon.)


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