It is important to note that not all PFC power supplies will cause the UPS overload. However, the incompatibility is most acute
in the one of the following situations:
• A large server class PFC supply (e.g. rated 500W or more) is used with a Back-UPS or Smart-UPS SC.
APC recommends that a true, pure sine wave, server class UPS be used..... ...However if, a [non-pure/simulated/steppe
d sine wave UPS like] Smart-UPS SC or Back-UPS RS is to be used, the UPS should be sized accordingly.
Because of the way active PFC’s operate, they can sometimes overload the UPS with momentary high inrush current. This can occur when the UPS transfers from online to on-battery operation, creating a momentary loss of power (<8ms). The PFC supply may respond by temporarily drawing an excessive amount of current.
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