What is a UPS system?

In this article, you will learn about functionality, main parts and different types of the Uninterruptible Power Supply systems or UPSs.

So, what is an Uninterruptible Power Supply, or UPS?

An Uninterruptible Power Supply is a device that is used to keep computers and equipment safe when there is a loss, or a significant reduction, in the primary power source.

To achieve this, the UPS houses several batteries that take over when it detects a loss or reduction in available power.

Once this is detected, the control is transferred over to the batteries, and via an inverter, the batteries DC voltage is converted into AC for the devices.

In reality, it doesn’t have to be computers systems and equipment that are kept alive by UPS. It could be anything from a fish tank, to a foot massager!

We aren’t just talking about plain power outages, lights off, TV off, everything, but we can sometimes get spikes in power where a sudden drop can assure our devices are momentarily powered off, or something known as a brown-out.

This is where there is a voltage drop, either unintentionally, or intentionally. Sometimes in an emergency, there is a load reduction, caused intentionally.

With an Uninterruptible Power Supply, all of our systems can run as normal to compensate for the reduction in power. Clever!

The amount of time the UPS can sustain a system for can vary, but it allows the opportunity for the issue to be resolved, or at the very least, allows for the systems to be shut down in a controlled manner.

Even the simplest UPS is made up of a number of parts. We’re going to look at the standard parts that you can find in a basic UPS system.

Standard Parts of a UPS System

Since a UPS is a system that uses batteries to power a system should the supply be compromised; we, of course, have batteries and a battery charger.

Since the batteries use DC current and our incoming supply is AC current, we need to convert DC to AC using an inverter.

Finally, we need a way of switching between the AC incoming supply and battery power.

For this, we use something called a “transfer switch”.

So, to break it down, these are the parts we need for a basic UPS system:

– Batteries

– Battery Charger

– Inverter

– Transfer Switch

A UPS provides second level surge protection, but although it does provide some protection, it should usually be used alongside an adequate Surge Protection Device (SPD) to extend the life of the UPS as well as the attached equipment. 

Sounds simple, right?

We’ve already discovered a basic UPS system and what parts it includes.

Now, we’re going to find out all about the different types of Uninterruptible Power Supplies and what their typical functions are.

Different Types of Uninterruptible Power Supplies

1. Standby (Offline) UPS

Firstly, and the most common in smaller systems is the Standby or Offline UPS. This is the one you would normally use on a personal computer for example.

The Standby UPS lays in wait for its time to spring into action, and once there is a power failure, it takes control.

The Standby UPS tends to be the most cost-effective UPS available.

2. Line-Interactive UPS

Next up, we have the Line-Interactive UPS. You’ll find this type of Uninterruptible Power Supply in small business infrastructure.

It is very similar to a Standby UPS but with the added ability to regulate voltage automatically.

This means that it monitors the incoming supply and can help out if it detects that the voltage is a bit low, or a spike is causing it to go too high.

It can add or subtract power in this way to make the output to our devices constant! Very smart!

This type of UPS is particularly useful for the brown-out situation we’ve already mentioned, or power spikes or surges.

3. Online Double-Conversion UPS

Now we have the Online Double Conversion UPS. Don’t let the name put you off!

This type of UPS is efficient as the primary source of power isn’t the incoming supply, rather it is the battery power.

So when we have a power outage, there is no transfer switch to close, meaning no time to switch that you can get with the other type of UPSs.

When the incoming supply is ON, the batteries simply charge up.

It’s called “double-conversion” because it converts the AC incoming supply to DC, and then the inverter converts it back to AC for the output.

In general, it ensures a far higher degree of isolation of the load from the irregularities on the mains supply.

These are the most common types of UPS available. Of course, there are other types that fit a particular form or function, but these tend to be for more specialist needs.


More advanced UPSs can regulate the voltage to prevent damage to equipment in case of a brown-out or a power surge.

We now have a good understanding of what parts are used to make up a UPS. Those parts are:

– Batteries

 Battery charger

– Inverter

 Transfer switch

Finally, we know that an Online Double-Conversion UPS is the most efficient as it doesn’t need a transfer switch as the primary source of the power goes through the batteries!

That’s it for this article! I hope you enjoyed learning about UPS systems, why we use them and what they are used for.

Here at RealPars, our team of experts is on hand to answer your questions and respond to your feedback. We’d love to hear your suggestions for topics you want our team to cover.

Got a friend, client, or colleague who could use some of this information? Please share this article.

The RealPars Team
By James Jowett

By James Jowett

Automation Engineer

Posted on Jul 29, 2019

By James Jowett

Automation Engineer

Posted on Jul 29, 2019

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