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ITFrequently Asked Questions · UPS
Can a UPS be used with a generator?
Yes, as long as the generator provides stable voltage and frequency. Some UPS units have dedicated settings for working with generators.
Pairing a UPS with a generator is very common: the UPS covers the first seconds or minutes until the generator starts and stabilises, and then the generator powers the UPS for as long as the outage lasts. This way the loads do not even notice the outage.
The difficulty is that many generators, especially small portable ones, show fluctuations in frequency and voltage, particularly when the load changes suddenly. The UPS may then treat the input as unsuitable and keep switching back to battery, draining it. Dedicated generator settings widen the accepted input frequency range to prevent this. Online UPS units usually work better with generators because they isolate the load from the input.
Practical tip: the generator needs a good power margin above the UPS rating, because the UPS draws extra current to charge its batteries and has its own losses; the required ratio depends on the UPS type and is best confirmed with the manufacturer. A common mistake is testing the combination for the first time during a real outage. Run a test with a real load beforehand.
