An online UPS (also called a double-conversion UPS) sits between your mains electricity and your devices, constantly running incoming power through a battery charging circuit and inverter. This means your equipment always draws power from the inverter output rather than directly from the wall, giving complete isolation from mains problems.
How it differs from other UPS types:
- Standby UPS: Only activates when mains power fails, leaving a brief gap (typically 4-10ms) where devices lose power.
- Line-interactive UPS: Monitors voltage and adjusts output without full conversion, slower response than online.
Why it matters: Online UPS systems eliminate switchover delays entirely, making them essential for servers, medical equipment, and sensitive electronics intolerant of any power interruption. They also condition power continuously, removing spikes, sags, and harmonic distortion that degrade equipment lifespan and cause data corruption.
Key trade-offs: Online units cost more than standby models and generate more heat because the inverter runs constantly. They also waste slightly more energy during normal operation since power converts twice (AC to DC, then back to AC) rather than bypassing conversion when mains is stable.
What to check: Load capacity in watts or VA (volt-amperes), battery runtime at full load, efficiency rating, and whether the unit can operate in eco mode to reduce energy waste. For UK installations, verify the unit matches local voltage standards (230V single-phase).