UPS & Uninterruptible Power

A UPS does two jobs and they are often confused. The first is ride-through: carrying the load through the seconds between a mains failure and a generator taking over, or through a dip too short for anything else to notice. The second is conditioning: presenting clean, regulated power to equipment regardless of what the incoming supply is doing. Only an online double-conversion topology does the second properly, which is why it is specified for IT loads even though line-interactive units cost less.

Sizing is where most installations go wrong. A UPS matched to present draw has no headroom, and battery autonomy quoted at half load is roughly halved when the room fills up — so a unit advertised at thirty minutes can deliver well under ten by the time it is doing the job it was bought for. Present load, expected growth and required autonomy are three separate numbers and all three have to be stated.

Batteries are also the part that ages. Valve-regulated lead-acid strings degrade steadily and fail suddenly, usually under the load they were installed to protect against, so periodic testing and a replacement plan are part of the design rather than an afterthought.