We hope to answer some of the most popular questions regarding UPS systems and power protection. If your question remains unanswered, please contact us directly.


An Uninterruptible Power Supply is a device that sits between a power supply (e.g. a wall outlet) and a device (e.g. a computer) to prevent undesired features of the power source (outages, sags, surges, bad harmonics, etc.) from the supply from adversely affecting the performance of the device.

There are basically three different types of Technologies, all of which are occasionally passed off as UPSes. 1 - Stand by : The standby UPS is the simplest and least expensive UPS design. In fact, some don't even consider a standby UPS to really be a UPS, calling it instead a standby power supply (SPS). However, many of the most common consumer-grade devices marketed as UPSes, particularly on the lower end of the budget scale, in fact use this general design. They are sometimes also called offline UPSes to distinguish them from Online Ups In this type of UPS, the primary power source is line power from the utility, and the secondary power source is the battery. It is called a standby UPS because the battery and inverter are normally not supplying power to the equipment. The battery charger is using line power to charge the battery, and the battery and inverter are waiting "on standby" until they are needed. When the AC power goes out, the transfer switch changes to the secondary power source. When line power is restored, the UPS switches back.

2 - Line Interactive The line-interactive UPS uses a totally different design than any type of standby UPS. In this type of unit, the separate battery charger, inverter and source selection switch have all been replaced by a combination inverter/converter, which both charges the battery and converts its energy to AC for the output as required. AC line power is still the primary power source, and the battery is the secondary. When the line power is operating, the inverter/converter charges the battery; when the power fails, it operates in reverse. The main advantage of this design is that the inverter/converter unit is always connected to the output, powering the equipment. This design allows for faster response to a power failure than a standby UPS. The inverter/converter is also normally fitted with circuitry to filter out noise and spikes, and to regulate the power output, providing additional power during brownouts and curtailing output during surges. The line-interactive UPS is an improved design that is commonly used in units for home and business use, available in sizes up to 3,000 VA or so. It is superior to the standby UPS, but it still has a transfer time, and thus does not provide protection as good as the Online Ups

3 - Online The online UPS, sometimes called a true UPS, is the best type you can buy. Paradoxically, it is both very similar to, and totally opposite to, the least-expensive type, the standby UPS. It is very similar to it in that it has the same two power sources, and a transfer switch that selects between them. It is the exact opposite from the standby UPS because it has reversed its sources: in the online UPS the primary power source is the UPS's battery, and utility power is the secondary power source! Of course, while seeming small, this change is a very significant one. Under normal operation the online UPS is always running off the battery, using its inverter, while the line power runs the battery charger. For this reason, this type of UPS is sometimes also called a double-conversion or double-conversion online UPS. This design means that there is no transfer time in the event of a power failure--if the power goes out, the inverter (and its load) keeps chugging along and only the battery charger fails. A computer powered by an online UPS responds to a power failure in the same way that a plugged-in laptop PC does: it keeps running without interruption, and all that happens is that the battery starts to run down because there is no line power to charge it. You may ask yourself, why bother having the secondary power path (the dashed line in the diagram above) if you are always running off the battery anyway? The reason is that this provides backup in the event that the inverter fails or stutters due to some sort of internal problem. While unusual, this can happen, and if it does, the unit will switch to the filtered, surge-suppressed line power. In this event, the matter of transfer time comes into play again, just as it does when a standby UPS reacts to a power failure. Of course, power failures are much more common than inverter failures. There is another key advantage to having the equipment running off the battery most of the time: the double-conversion process totally isolates the output power from the input power. Any nasty surprises coming from the wall affect only the battery charger, and not the output loads.

A UPS has internal batteries to guarantee that continuous power is provided to the equipment even if the power source stops providing power. Of course the UPS can only provide power for a while, typically a few minutes, but that is often enough to ride out power company glitches or short outages. Even if the outage is longer than the battery lifetime of the UPS, this provides the opportunity to execute an orderly shutdown of the equipment. Advantages:

  • 1. Computer jobs don't stop because the power fails.
  • 2. Users not inconvenienced by computer shutting down.
  • 3. Equipment does not incur the stress of another (hard) power cycle.
  • 4. Data isn't lost because a machine shut down without doing a "sync" or equivalent to flush cached or real time data.

A UPS traditionally can perform the following functions:

  1. Absorb relatively small power surges.
  2. Smooth out noisy power sources.
  3. Continue to provide power to equipment during line sags.
  4. Provide power for some time after a blackout has occurred

In addition, some UPS or UPS/software combinations provide the following functions:

  1. Automatic shutdown of equipment during long power outages.
  2. Monitoring and logging of the status of the power supply.
  3. Display the Voltage/Current draw of the equipment.
  4. Restart equipment after a long power outage.
  5. Display the voltage currently on the line.
  6. Provide alarms on certain error conditions.
  7. Provide short circuit protection.

That depends on how big a UPS do you have and what kind of equipment it protects. For most typical computer workstations, one might have a UPS that was rated to keep the machine alive through a 15 minute power loss. If it is important for a machine to survive hours without power, one should probably look at a more robust power backup solution that includes a generator and other components.
Even if a UPS powers a very small load, it must still operate its DC (battery) to AC converter (the inverter), which costs power. A rough extrapolation from APC's documentation, leads me to guess that its 2000 VA UPS can operate its own inverter (with no extra load) for just over 8 hours. A 1250 VA UPS could run its converter for about 5. These are very rough guesses based on information provided by one vendor for one vendor.

The UPS and inverter both provides the backup supply to the electrical system. The major difference between the UPS and inverter is that the UPS switches from the main supply to the battery immediately, but the inverter takes much longer.

Yes. You can monitor directly from the UPS to a computer via the RS232 or USB ports, which comes as standard in most new UPS°«s. You can also monitor the UPS over a network, to do this you will need an optional SNMP/Network card. The UPS can then be viewed with your browser or with the use of free UPS software. Email and SMS messages can be automatically sent to nominated addresses/numbers if the UPS changes status. Return to our FAQ page

A non-critical load, is an electrical device or devices, that aren°«t key to keeping a business running or won°«t be damaged by a power cut. In short, it doesn°«t matter if these device lose power in an outage.

UPS battery back-up times can vary from 2 minutes, to many hours. It all depends on what you need. The main question to ask before deciding on the UPS backup time is:

In the event of a long power outage °»what do we want to do°…?

We advise that the UPS batteries are checked/tested/discharged periodically to ensure that they still functioning correctly.

Small to medium UPS batteries generally have a 4-5 year design life, this can vary dependant on the number and depth of discharges together with the environmental conditions i.e. temperature.

For larger UPS systems batteries with an 8-10 year design life are generally used

Simply shut down the servers and wait until power is restored. In which case °»how long does it take to shut down the critical equipment?°… Have a longer backup time in order to shut down a large database, or manually shut down certain applications. In which case °»how long does it take?°… Keep key personnel, the telephone system or communications to remote sites operational. In this case a longer backup time will be required. °»How long?°…

Phases of a UPS, such as a single-phase UPS or a three-phase UPS, describe the number of electrical phases that a UPS receives and transmits. Electrical utilities generate three-phase power because that is the most efficient way to transport electricity over long distances.

For larger power consumers, such as large data centers, industrial manufacturing and hospitals, the power stays as three-phase, requiring a three-phase UPS. For smaller power consumers, including residential or office buildings and most K-12 schools, the power is converted to single-phase power.