Figure 65. Path Of Current Through The Ups In Battery Mode - Eaton Power Xpert 9395P-1100/1100 Installation And Operation Manual

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Understanding UPS Operation

6 6 . . 2 2 . . 6 6 B B a a t t t t e e r r y y M M o o d d e e

The UPS automatically transfers to Battery mode if a utility power outage occurs, or if the utility power does not

conform to specified parameters. In Battery mode, the battery provides emergency DC power that the inverter

converts to AC power.

Figure 65

shows the path of electrical power through the UPS system when operating in Battery mode.

During a utility power failure, the rectifier no longer has an AC utility source from which to supply the DC output

current required to support the inverter. The input contactor K1 opens and the battery instantaneously supplies

energy to the battery converter. The converter either bucks or boosts the voltage so that the inverter can

support the customer's load without interruption. If bypass is common with the rectifier input, the backfeed

protection contactor K5 also opens. The opening of contactors K1 and K5 prevent system voltages from

bleeding backwards through the static switch and rectifier snubber components and re-entering the input

source.

If the input power fails to return or is not within the acceptance windows required for normal operation, the

battery continues discharging until a DC voltage level is reached where the inverter output can no longer

support the connected loads. When this event occurs, the UPS issues another set of audible and visual alarms

indicating SHUTDOWN IMMINENT. Unless the rectifier has a valid AC input soon, the output can be supported

for only two minutes before the output of the system shuts down. If the bypass source is available, the UPS

transfers to bypass instead of shutting down.

If at any time during the battery discharge the input power becomes available again, contactors K1 and K5 close

and the rectifier begins to supply DC current to the converter and inverter. At this point, the unit returns to

Online mode. Depending on the total load and the duration of the battery discharge, battery current limit alarms

may be seen for a short time due to the current required to recharge the battery.