Uninterruptible Power Supply

A UPS, or uninterruptible power supply, provides a source of emergency power when utility power fails and a measure of line conditioning by smoothing out spikes. Unlike auxiliary or emergency power systems, it can provide protection the moment the power fails. The UPS provides a power supply backup that can allow power for anywhere from 5-30 minutes, depending on the load draw. This can allow enough time to turn auxiliary power on, possibly begin to operate under utility power again, or shut the equipment off safely.

The typical use for a UPS is to help protect computer systems including data centers, telecommunications equipment, and other equipment where anything from data loss or interruptions in business to physical injury could occur. UPS units vary in capability from 200 VA units, for powering a single computer, to several megawatts units for data centers or buildings.

Closeup of an uninterruptable power supply (UPS) in black with selective focus

Types of power problems which a UPS may address
UPS units may address a number of different power issues and are categorized accordingly. Some manufacturers will classify a unit according to how many problems they can help with. Among the possible problems that a UPS might address are:

Technology and capabilities
There are three general categories of UPS systems: online ups, line-interactive ups, and standby ups. The online UPS takes the utility company AC input and rectifies this to DC, which runs through the battery or battery strings. This DC is then run through an inverter to change it back to AC to power the equipment. Thus, it provides a “double conversion” of the current. A line-interactive UPS, in normal mode, while providing utility power, allows an instant switching capability to DC power, through the use of an inline inverter, if utility power should fail or there should be a significant under-voltage or over-voltage. With the standby, or “offline” UPS, power is provided by the utility company only, until there is a significant power loss. In which case, the battery power of the UPS is then utilized. The standby UPS and line-interactive UPS are the most common and least expensive.

To ensure adequate power supply backup is in place for your computer, consider adding an uninterruptible power supply (UPS). A UPS will, in the event of power failure, secure backup power supply for your system by preventing electrical power surges or drops from adversely affecting your computer. The UPS charges the battery while your computer runs during normal conditions, but when the power goes out it will provide additional power (usually at least 10 minutes), allowing you to safely complete your work, save your files, and power off your computer. UPS devices are not required to run your computer effectively, but it’s a good idea to include one as a safety measure to help protect your data from potential damage caused by power interruptions.

UPS Power Types

With a standby, or offline, device, power runs directly from the AC outlet unless a power failure or drop occurs. When your system experiences low voltage or power loss, a stand-by UPS will provide backup power supply by switching to battery backup for a specific length of time, usually around 10 minutes. A stand-by power supply is effective in protecting your computer from abnormal power situations, and it is also the most cost-effective of the three UPS devices.

The next option is a line-interactive UPS which, as the most recent version of UPS devices, provides all the features of a stand-by device but also automatically regulates voltage if your system experiences abnormal voltage conditions. During a brownout, or power dip, a line-interactive device provides a voltage boost instead of accessing battery power, which helps extend the life of the battery. The battery is only used during a power failure. When comparing price and functionality, this power supply is in the middle of a stand-by device and an on-line device.

Finally, an online UPS is the top of the line power supply backup. Like the previous two devices, the on-line UPS will also protect your system in the event of a power failure, but it also uses a unique double-conversion technique to convert the power entering the UPS from AC to DC. After the on-line UPS device conditions the power, effectively removing the typical noise, sags, or surges that can cause errors and data loss, it then converts the power back to AC before the power leaves the UPS. Power constantly runs through the battery system, eliminating transfer or switch time to battery mode should a blackout occur. Of the three available types of UPS devices, the on-line UPS provides the highest quality of protection.

Choosing the right backup power supply depends on your needs, and you should consider the best kind of protection you want in place for your system before making a decision. A stand-by device will provide adequate protection for those who don’t want to spend a lot and have less than critical requirements. An on-line unit is best for those who can afford to spend a little more and desire unlimited battery backup. A line-interactive device is a good choice, in terms of performance and affordability, for those somewhere in between. When comparing UPS devices, you should also consider warranty features, the length of time battery power lasts during an outage, and whether or not you can replace the battery should the unit ever require it.

No power transfer switches are used in the Online UPS, because the inverter is always connected to the batteries. A power failure causes the rectifier to drop out of the circuit and power to be supplied by the batteries with no change in voltage. When utility power is available, the rectifier is brought back in the circuit and the batteries are able to be charged. Another feature of the Online UPS is that it may limit the charging current of the batteries to prevent overheating them and boiling the electrolyte off.

The Online UPS provides advantages over the Standby and Line-interactive UPS units. It maintains output voltage and output frequency irrespective of input voltage and input frequency. The other two filter the input power, but don’t provide as close controls on output voltage and frequency. The Online UPS offers power supply backup for typically 5-30 minutes, but this can be expanded to several hours.

Redundancy
When reliability is really critical, a single point for failure could come from using a single UPS. Integrating UPS modules provides a redundancy solution. Also, in cases where redundant power supplies are used, like with computer servers, the power supplies can be plugged into separate UPS units to provide protection in case of a power supply failure or a UPS failure. Plugging each power supply into a separate circuit breaker enhances this practice.

UPS Power Considerations

In situations where an interrupted power supply could be dangerous or even fatal, a UPS or Uniterruptible Power Supply device is often used. A UPS is different from an emergency power system or a standby generator in that it provides power instantly should the utility supply stop for some reason. An emergency power system or standby generator generally takes a few seconds or even minutes to begin functioning. A UPS is also sometimes referred to as a battery back up or power supply back up.

A UPS system is not designed to provide power for an extended period of time. Instead, the systems are to provide a sort of bridge until the utility power supply is fixed or until an emergency power system or standby generator can begin functioning properly.

UPS devices are not limited as to where they can be used, but are usually used in hospitals, nursing homes, airports and other places where it is imperative to maintain a constant supply of power. The devices also come in a range of sizes from those designed to back up a single computer to those designed to back up entire buildings or data centers.

There are many types of power supply back up systems. Some are external, some internal, various designs are stored only indoors, others have special parts and are stored outside. Generally UPS systems are classified as on-line, line-interactive and standby. The size, design and type of system determine how long the UPS will work. Generally, when a UPS is installed, an entire plan of action is devised in the case of a power outage.

One last though

The standby UPS system is the least expensive and also the least reliable type of UPS. Some experts believe that a standby power supply backup is worse than having no backup at all, because it may give a false sense of security. The line-interactive type of UPS is more complicated, more expensive and also more reliable than the standby type. Line-interactive systems make use of a special type of electrical transformer called an autotransformer.

The on-line type of UPS was once reserved for large data centers and very sensitive situations. Advances in technology have made it more affordable and available to average consumers. On-line systems are more expensive and have the capacity to carry much more currant and to run continually. New technologies are constantly emerging in this field as well that will continue to improve the performance of UPS systems.

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