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Do You Need A UPS? (Page 3)3. Online UPS This design is considered to be a "true" UPS. Unlike the other types of UPS, this one uses the battery as its main source of power and the line power is the secondary source of power. When line power goes out, the UPS does not have to convert from one power source to another. It just stops charging the battery. This is similar to the way laptops react when they are unplugged from line power. When there isn't any line power the battery will keep powering the system until its stored power is depleted. Since this type of UPS design runs off the battery, the equipment plugged into it will always maintain a constant flow of power. Any surges or brownouts will be taken in at the battery charger and not passed on to the equipment.
Simplified Diagram of an "Online" UPS
These UPSs are often referred to as a "double-conversion" or "double-conversion online" UPS because they convert from AC to DC (battery charger) and then has an inverter to convert DC back to AC, for external devices. Although this method gives a very steady, "clean" flow of power, much of the power is dissipated as heat. This reduces efficiency. In addition, the battery is being used all the time, not just during a power failure like other types of UPSs. To combat this shortcoming, a new design called a "delta-conversion" online UPS was created. In this design, the battery charger is replaced with a delta converter. Instead of providing all of the output from the battery under normal circumstances, some of it is provided directly by the delta converter from the input line power. When there is a power failure, the delta converter stops operating and the unit acts like a regular double-conversion online UPS since the inverter is also running off the battery all the time. Being more complex, online UPS units generally costs more than offline units. They are generally used only in larger and mission-critical installations. |
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