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UPS: types and selection

Uninterruptible power supplies: offline/line-interactive/online types, power and runtime calculation, batteries, selection for boilers and computers.

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UPS types

TypeTransferOutputApplication
Offline4–10 msMains + stepped sineComputers
Line-interactive2–6 msStabilized mainsServers, boilers
Online (double conversion)0 msPure sine, stabilizedServer rooms, medical, boilers

Power calculation

P(VA) = P(W) / cos φ (0.6–0.7 for computers, 0.8 for boilers). Add 30–50% for inrush currents. Runtime: T = C×U×η/P with η ≈ 0.85.

Rule: run the UPS at 40–70% load.

Selection

TaskRecommendation
Computer / routerLine-interactive 600–1500 VA
Gas boilerOnline 1–3 kVA pure sine + external batteries
Server / NASOnline 1–3 kVA expandable
Whole house (short)Online 5–10 kVA + generator/ATS

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Data is for reference. Final design decisions must follow current regulations and a qualified engineer.