Q: The basic differences between common UPS types:

The term UPS stands for uninterruptible power supply (or uninterruptible power source). UPS systems are utilised in various applications mainly incorporating environments where unexpected power disruption can cause injury, fatalities, serious business disruption or data loss.

UPS systems have two main applications.

1. Firstly, they protect against brown outs* and black outs.
This is achieved by providing an instantaneous flow of power to the product when it's usual source fails.

2. The second function of a UPS is to 'clean' the power to the product.
This means a constant and reliable flow of power to the end device. The way this is achieved varies from type to type.

On a day to day level, UPS systems are used to protect personal PC's and sensitive peripheral equipment (printers, faxes etc.) On a corporate level. UPS systems protect high end data/communications equipment. There are three common types of UPS systems you may come across:

1. Off-line/Standby
2. Line Interactive
3. Double Conversion/Online

1.Off-line/Standby

The most basic of UPS systems, it provides the most basic of battery back-up and surge protection. When a brown-out/black-out occurs these UPS systems can take up to ¼ of a second to switch over to back-up power. These types of units are usually designed for use on personal computers. The run-time (depending on the system) can range up to 20 minutes but is generally around 2-minutes. This gives the user enough time to save and log off (or shut down) a unit without damage.Off-line UPS systems cannot have battery cells added to increase capacity. They are also quite temperamental. This is due to the fact that during a brown out/black out the battery is supplying the full load without continuing to be charged.

2.Line Interactive

Line interactive UPS systems are more reliable then off-line units and are more resilient to continuous brown-out and black-out scenarios. Their make-up allows them to adjust the output to supply instantaneous power (during a brown-out) and suppress power spikes (during a surge) all while continuing to charge the battery. Due to this the battery cells life expectancy is increased significantly and the end users cost (over time) is reduced. Extra battery cells can be added to this unit to increase it's capacity.

3.Double Conversion/Online

Unlike the other two types, double conversion/online UPS systems are able to completely isolate the attached device from the power supply. What this means is the output power to the device is in no way governed by the fluctuations, frequency and irregularities of the input power supply. In this type of UPS the battery is always connected to the load so there is no delay for the battery to supply the power during a brown-out or black-out. Extra battery cells can be added to this unit to increase it's capacity. This type of UPS can be designed to provide up to 20hours of power. 

Definitions:
Brown Outs - Where power voltage dips but does not completely cut off.