The Basic UPS (Uninterrupted Power Supply) Guide

A UPS (Uninterrupted Power Supply) is a power supply that includes a battery to maintain power in the event of a power outage. Most UPS units will also filter and regulate the utility power. A UPS can be used on most electronic equipment, although this article will focus mainly on its use with computers.

There are basically three types of UPSs to choose from. Keep in mind that each manufacturer has their own design and changes. The types are as follows:

1. Offline (Standby) UPS
The standby UPS is the simplest and least expensive UPS design. Getting it's primary power from the AC line (i.e. your outlet), this type of UPS switches over to the backup battery automatically when any drop in voltage is detected. When the power is restored, the UPS then switches back. This "no frill" UPS usually has nothing to regulate the electricity although a few manufacturers may include some sort of line filter.

A "ferroresonant standby" UPS is an improvement on the design of the standby UPS. The ferroresonant UPS uses a ferroresonant transformer to switch from line power to battery power. By using this technology there is a source of stored energy that is used during that fraction of a second while the unit switches between line power and battery power. This was once one of the most common UPS designs, and are still made by some manufacturers. Today, most manufacturers have abandoned this design, claiming that it is inefficient, and favor the "online" UPS for models in the range of 1,000 VA or higher.

2. Line-Interactive UPS
Hailed by some to be the most efficient UPS, the line-interactive UPS is one of the most popular designs used today for computer protection. Although some manufactures sell line-interactive UPSs which are no more than an offline UPS with a regulator added, the basic line-interactive UPS has a bi-directional inverter/charger which is always connected to the output of the UPS, and uses a portion of AC power to keep the battery charged. When the input power fails, the transfer switch disconnects AC input and the battery/inverter provides output power. This gives a faster response to a power failure than an offline UPS.

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.

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.

It is advisable to look over the specifications of the UPS you are considering to buy. If you need more backup time, then you must buy a larger UPS. It must be noted that buying a larger UPS does not always give you more backup time. The size and type of battery used in the UPS has a lot to do with it. UPS batteries are rated in Ah (ampere-hours). Ah represents the amount of energy a battery can hold. This measurement helps determine how long the battery will power the equipment it is used in. The more 'Ah' the longer the run time.

With the prices of UPSs dropping all the time, there is no reason to let your computer go unprotected.

About the author:
Jonathan Kremer has over 25 years experience in the electrical field. For more tips and articles please visit http://www.megavolt.co.il