What is the transfer time of a UPS?

Transfer timeGlossary · UPS technologyTransfer TimeThe brief power gap when a UPS switches from mains to battery, typically 2–10 ms for line-interactive models and zero for online ones. is measured in milliseconds (ms) and shows how long the power gap lasts when the UPS switches from the mains to the battery. In Offline (StandbyGlossary · UPS technologyOffline (Standby) UPSA UPS that leaves the load on the mains and switches to battery only when the mains fails, with a short transfer time; the simplest and cheapest topology.) and Line-Interactive UPS units it is typically a few ms, usually under 10 ms. In double-conversion Online UPSGlossary · UPS technologyOnline (Double Conversion) UPSA UPS that continuously converts incoming AC to DC and back to AC, so the load is always fed by the inverter with clean, stable power. units the load is fed continuously by the inverter, so there is no transfer when the power fails.

Most computer power supplies can ride through such a short gap thanks to their capacitors, which is why a Line-Interactive UPS is usually enough for a home or office. More sensitive equipment, such as servers, medical devices or industrial control systems, as well as sites with poor-quality mains, benefit from an Online UPS, where the output never drops at all.

Practical tip: compare the transfer time on the datasheet, especially if you are powering equipment with little tolerance for interruptions. A common mistake is confusing transfer time with runtime: the first is about how quickly the UPS takes over, the second about how long it can power the load from the battery.