Transfer Time

Transfer time measures the brief power gap that occurs 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 usually a few milliseconds, roughly 2–10 ms, while in double-conversion (online) UPS units it is zero.

Most modern computer power supplies ride through such a short gap without restarting. More sensitive are some older or low-cost power supplies, medical and laboratory instruments, and equipment with relays or contactors that may drop out during the transfer.

If your equipment restarts at every brief outage even though it is connected to a UPS, check the model's transfer time. Often the solution is an 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..