Understanding UPS Operation
3.3 Battery Mode
The UPS transfers to Battery mode automatically 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. When the UPS switches to Battery mode, the alarm indications depend on the cause and condition of the battery charge. The length of time the system can operate in Battery mode depends on load configuration and the battery charge.
Figure 3-3 shows the path of electrical power through the UPS when operating in Battery mode.
Bypass
Bypass
Input
K4
| Rectifier | Inverter |
Rectifier | CB1 |
|
|
| |
Input |
|
|
K3 | Output |
| |
(Closed) |
|
Transformer |
|
Path of electrical power
Battery
Figure 3-3. Path of Current Through the UPS in Battery Mode
When the discharging battery voltage reaches the lower limit of UPS operation capability, the critical load transfers to Bypass mode if it is available. If Bypass input is not available, a “Shutdown Imminent” warning occurs. The warning time before critical load loss occurs is approximately two minutes, depending on load configuration and the battery charge.
If incoming power returns to within specified parameters, the UPS automatically returns to Normal mode and alarm indications clear. However, the process of returning to Normal mode is not instantaneous. The rectifier gradually draws increasing power from the incoming utility until Normal mode is achieved.
EATON Powerware® 9315 UPS |