Minuteman UPS CPE 2000 Chapter Four The Working Principle of the UPS, When Utility is Normal

Chapter Four: The Working Principle of the UPS

4.1. When Utility is Normal

The working principle of the UPS under normal Utility conditions is illustrated as follows:

RECTIFIER

O/P

OUTPUT

--- 4-1 ---

When Utility is normal, the AC source is rectified to DC, partially fed into the charger to charge the battery and partially fed into inverter. The inverter reverts the DC to AC to supply energy to the output load. The Utility LED and Inverter LED will illuminate.

4.2. When Utility is Abnormal

The working principle of the UPS under abnormal Utility conditions is illustrated as follows:

O/P

OUTPUT

--- 4-2 ---

When Utility is abnormal, the UPS will direct the battery energy to the Inverter. The charger and AC/DC converter will turn off. The inverter will revert the DC to AC to supply power to the output load. The Inverter LED will illuminate.

When the Utility power returns to normal, the AC/DC converter and the charger will turn on. The DC/DC converter will turn off. It has the same working principle as figure 4.1.

During a blackout, the UPS will work as illustrated in figure 4.2. When the battery is low, the alarm will beep continuously until the battery is depleted and the UPS shuts down. The Low Battery Cut-Off protection turns the UPS off to prevent discharging batteries to an unsafe level. The Inverter LED and the Battery Low LED will be illuminated until the UPS shuts down. The UPS will Auto-Restart when the Utility power returns to normal. This is the same working principle as figure 4.1.

4.3. Overload Condition

The working principle of the UPS when overloaded is illustrated as follows:

O/P

OUTPUT

--- 4-3 ---

Normally, an inrush current is generated when turning on the connected equipment.

If the UPS is 105~120% loaded, it will switch to the Bypass mode in 60- seconds.

If the UPS is 120-150% loaded, it will switch to the Bypass mode in 10- seconds.

If the UPS is over 150% loaded, it will switch to the Bypass mode immediately.

The Utility LED, the Bypass LED and the Overload LED will be illuminated. If overload condition is removed the UPS will switch back to the On-Line mode automatically.

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