Top 5 interesting facts about UPS

Facts about Uninterruptible Power Supply

You probably know how Uninterruptible Power Supplies work and what their purpose is, but we have the top 5 interesting facts about UPSs that you probably didn’t know!


UPS facts - UPS inventor

The history of Uninterruptible Power Supplies is somewhat a mystery – nobody can name one person or one date when UPSs systems were invented. There were many theorists and scientists involved in research and studies, however nobody  can claim to be the inventor of UPS.



UPS facts - ups patent
source: google/patents

This rather amusing acronym stands for “Apparatus for Maintaining an Unfailing and Uninterrupted Supply of Electrical Energy”, which is a first ever UPS patented in 1934 by John J. Hanley. Mr. Hanley mentions in the document that the invention is to be used with fire alarms and other safety systems to protect properties and lives. It is amazing how far UPSs have come since then and how the variety of applications widened since 1930s. The AMUUSEE was an ancestor of UPSs as we know them now. We are certainly grateful that UPSs are now called Uninterruptible Power Supply rather than the tongue twister that is used to be back in the day.

You can read the whole patent document at google/patents.


UPS facts - largest ups in the world

The largest Uninterruptible Power Supply system in the world is a 46-megawatt system in Alaska.  The system is called the “Battery Electric Storage System (BESS)” and is located in Fairbanks, Alaska where it powers the entire town! It can provide up to 15 minutes runtime at 26 megawatts, providing enough backup power until the generator comes on. The runtime is achieved by four battery strings, each containing 344 series of connected battery modules. That is one truly amazing UPS.


UPS facts - batteryA UPS is nothing without batteries. Did you know that majority of faults within UPSs are related to batteries? Good batteries matter and so to ensure your UPS provides maximum reliability, you need to organise for appropriate maintenance. Power Inspired Uninterruptible Power Supply systems come with VRLA batteries with 3-5 year design. This time is however approximate and depends upon many factors, including the environment in which the UPS is stored. You can see how to prevent premature battery failure in our previous blog.



UPS facts - TX Series Isolated UPS SystemsPower Inspired’s TX series provides unique safe UPS technology. The units contain an isolation transformer which protects from electric shock and ensures the UPS is isolated and safe. TX series units range between 1KVA – 10KVA, they have a small footprint and the design is highly modern and minimalistic. The larger units (3KVA, 6KVA and 10KVA) also come with wheels for ease of installation. TX series UPS are designed to provide highest degrees of power protection for laboratory, industrial and medical applications. More information about TX series can be found here.

UPS ECO mode – what’s so good about it?

UPS eco mode

All of our online double conversion UPS systems feature a setting option to run the UPS in an ECO mode. What does this mean? And is it beneficial for you? We will try to answer those questions for you.

An ECO mode in UPS systems essentially means that the UPS’s inverter is in a standby mode. It only kicks in if the mains power fails. By enabling ECO mode on your UPS it will basically have the same operation as a regular line interactive UPS.  In a nutshell, by enabling the ECO mode you’ll expose the load to raw utility power.

What’s good about it?

The ECO mode has some great advantages, such as efficiency improved from 94%-97% to 98%-99% and lower operation costs (up to 4% reduction on energy use). It may also prolong the lifetime of some of the UPS components due to the decreased operating temperature on these components – the UPS is in a bypass mode hence some components are not in use which may prolong their life span.

What’s bad about it?

However the ECO mode not only has positives, it also comes with some risks: the fact that the UPS must first detect power failure and then turn on the inverter results in a transfer time that in some critical applications cannot be tolerated. Unlike the standard (online) mode of fully featured online UPS systems (our VFI-T, VFI-B and TX series) where the switchover time is nonexistent, this may be an issue for some critical, highly sensitive equipment. The ECO mode can improve UPS efficiency by about 2%-4%, however at the cost of possible downtime due to the switchover time. The switchover time can last anywhere from 1-16 milliseconds during which time your equipment will be exposed to any power problems present on the mains. Some equipment may be okay to cope with the transfer time, however some more complex and critical loads may be unable to tolerate it.

The ECO mode comes with some other risks: Besides the risk of reduced electrical protection which may have a negative impact on reliability and possible operation issues, the UPS in ECO mode will switch to battery at any instance of power problem which may have been easily dealt with without reverting to battery using standard online mode. This may negatively affects the battery’s lifetime and wear.


These are the advantages and disadvantages of using UPS in an ECO mode. The ECO mode can improve efficiency and reduce operation costs of your UPS, however while choosing your default operation mode, you need to bear in mind all the associated risk and decide if your equipment can take on the risk. As an operator you need to thoroughly consider all pros and cons and decide what settings will work best for you.

Explanation of Buck and Boost in Line Interactive UPS Systems

LCD screen

A line interactive Uninterruptible Power Supply is characterised by its ability to raise the input voltage when it is too low, and to lower the input voltage when it is too high. This provides a degree of voltage regulation. This process is sometimes known as Automatic Voltage Regulation or AVR, however some manufacturers of AVR equipment may – and probably do – object to this as a line interactive UPS is a very loose AVR whereas a dedicated AVR device offers tight control on output voltages. A better description for a line interactive UPS System would be a “buck and boost” device.

Here in this article I’m going to try and explain what one of our UPS does and for this I’m going to take the VIS2000B, apply varying voltage to it and observe the unit response. The VIS2000B is a good choice as the LCD display lets us know both input and output voltage so we don’t need to add any multimeters to the circuit. We’re going to modify the input voltage by means of a variable transformer, or a Variac. If you’re trying this at home don’t use a dimmer switch as these work in a different waybuck&boost.

Firstly we set the variac to nominal voltage, connect to the VIS2000B and switch it on. The display shows input voltage on the left at 230V and the output voltage on the right at 230V.

This is normal operation and so what comes in, goes out. What we will do now is increase the input voltage and observe.

buck&boostAs the voltage is increased the output voltage matches the input voltage until the buck trigger threshold is reached. This is set to be around the maximum voltage that the utility should provide which is 230 +10% = 253V.

In our case at 252V the unit enters buck mode and reduces the high input voltage to 212V. [Also note that on VIS2000B the AC Mode indicator blinks.]

The lower threshold of voltage supplied by the utility is open to some debate. It is 230V -10% = 207V in much of Europe and was supposed to be the same in the UK. However the implementation date of about 8 years ago has come and gone and so officially in the UK the voltage is still set to be 230V – 6% = 216V. However other standards for products that are CE marked generally require equipment to be able to operate across the full spectrum of nominal voltages, so the output is aimed to be regulated within the realm of the EU, so 230±10% or 207V to 253V.

buck&boostRaising our test variac to as high as it could go saw the unit maintain in buck mode with the output voltage rising proportionally with the input. In buck mode the input voltage is reduced by a nominal 16% or so.

Raising the input voltage even higher results in the unit disabling buck  mode and reverting to battery operation.

buck&boostAs we reduce the input voltage the buck will at some point be deactivated and the unit will return to normal. There must be some hysteresis built into this or the unit would “chatter” eg switch constantly in and out at the threshold voltage.

In our test with the unit output reaching 207V a further reduction in input voltage caused the unit to switch out of buck mode and back into normal mode.

With the mains input voltage reduced further the output voltage tracks the input voltage until the boost threshold is reached at around the 207V mark.

buck&boostHere the mains input is raised by around 17-18% in order to maintain the voltage within the nominal range.

Further reductions in the input voltage will keep the unit in boost mode until the output voltage can no longer be maintained within tolerance and the unit will revert to battery operation.

Raising the voltage the unit comes out of battery mode, straight into boost which then is disabled when the input voltage reaches around 211V.

To summarise, a line interactive unit attempts to maintain the output voltage within regulated limits for as long as possible without dropping to battery power. This is an advantage of over offline UPS systems that will have no option but to drop to battery instead of providing regulation, which would resort in lost loads due to UPS switching off due to depleted battery, or diminished battery life if the unit is regularly switching in and out of battery mode. However, they do not provide tight output voltage control. To achieve this online double conversion UPS systems provide a constant fixed output voltage regardless of the input voltage level.

Additional Notes with regard to the VIS2000B

One of the drawbacks of UPS Systems is the need for them to prevent a build up of heat and so many are fitted with forced cooling fans. In our VIS2000B the unit fan activates when the unit is “active” that is, on battery but also when it is in buck or boost mode. Users may find their unit enters buck mode when their mains is around the 250V mark as this will be activated should the mains hit 252V even momentarily. Due to the hysteresis effects the fan will not be disabled until the lower threshold is reached which is around the 246V mark. If this occurs, briefly switching the unit onto battery power will clear the hysteresis effect.

Note that we can change the threshold somewhat to effectively shift the buck and boost points higher by around 10V or so. This prevents the unit entering a nuisance buck mode and also makes the minimum output voltage more within the current UK spec but this does mean that the unit will allow voltages of 260+V through, should these be encountered. This is a factory setting that the Power Inspired technicians would be happy to undertake for you if required.


Extended Run UPS Systems

Extended Run UPS Systems

Extended Run UPS Systems are Uninterruptible Power Supplies that can have additional battery packs added, or alternatively a large battery bank connected to achieve longer runtime.

However it is not just a process of continually adding battery packs until the desired runtime is achieved. This is because the UPS needs to recharge the batteries in a reasonable timeframe, and is why there is a recommended maximum to the number of additional cabs that can be fitted. For example, let us take a system with a built in 1A charger, and this is connected to it’s internal battery string with a 9Ah (~PAGE-Ampere Hour-~) capacity. This means in an ideal world with no losses, the charger can put 1Ah back into the battery each hour, thereby taking 9 hours to recharge. If we add an 18Ah battery pack to this, then the recharge time is now 27hours. Another 18Ah battery pack now extends this to 45 hours and so on.

Some Extended Run UPS Systems do not contain any internal batteries but a high capacity battery charger. These are designed for high capacity battery banks or the connection of many battery packs. For example a unit with a 5A charger can charge the 45Ah battery pack above in 9 hours.

Note that these recharge times are ideal. In reality charging lead acid batteries has inefficiencies that increase the closer to capacity the battery is charged. This is why battery recharge times are normally quoted to a value – for example 90% of charge.

Extended Run UPS systems