Home Office UPS Buyers Guide

An Uninterruptible Power Supply (UPS) is a device that sits between the mains socket and a computer, or a number of computers. Its job is to ensure the computers receive a consistent and clean power supply, whilst also protecting them from power surges and power failures. A surge could damage components within the computer and a failure could interrupt data being saved on the device, resulting in errors. The more mission-critical a computer is, the more it should be power protected by a UPS.

This guide will take you through how a UPS works, common features and the factors you should consider when looking to purchase one for your home office.

How a UPS Works

A UPS is a device that regulates mains power passing through it and provides emergency power when the input power source, typically the utility mains supply, fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide instantaneous or near-instantaneous protection from input power interruptions by means of one or more attached batteries. The battery runtime of most UPSs is relatively short - 5 to 15 minutes being typical—being sufficient time to bring an auxiliary power source online, or to properly shut down your computers and other devices.

A UPS designed for a home office environment is typically only going to protect a handful of devices - a computer (desktop, laptop or workstation), single or dual monitors and potentially an external storage device such as a NAS.

A typical UPS intended for home use will usually be a unit designed to sit on the floor and will feature regular UK 3-pin mains plug type connections, so computers, monitors and peripherals can simply connect the UPS and the UPS will then connect to the mains socket. Many UPS also have the ability to support and protect phone, network, serial port and data connections. Other features often include a battery replacement indicator, battery management and intelligent features such as automatic save and shutdown.

Types of UPS

There are three main types of UPS - Offline or Standby UPS, Online UPS and Line Interactive UPS. The Offline / Standby UPS is the most basic out of the three and is the only one we’ll deal with for home use. An offline or standby UPS provides light surge protection and battery back-up for the connected devices. Once it senses that the main power source goes beyond acceptable limits or fails, it will switch to the offline or standby battery. As the power source physically switches, there will be a small transfer time between the main power source and battery - usually around 25 milliseconds, so you won’t notice any downtime. It is also worth mentioning that there may be noise from the UPS when running in battery mode so placement may be a consideration. For more information on the other two types of UPS read our BUSINESS UPS BUYERS GUIDE.

UPS Sizing

There are several factors that influence sizing a UPS system, including the combined load of all the equipment the UPS will protect, scope for further system expansion and battery runtime requirement. Correctly sizing a UPS is crucial as it will not power all the connected devices in the event of a failure if the battery capacity is too small. To calculate the total power draw for the combined critical load that needs protecting, you should look at manufacturer specs, equipment labels or technical manuals to provide the information on volts, amps and power consumption in watts, that you’ll need - then follow these steps:

1. List the amps (A) & volts (V) values

Make sure to include all devices you want to protect. For example - laptop(s) or PC(s), monitor(s), external drive(s) or NAS, and router.

2. Multiply V by A to get VA for each device

Some devices may list their power requirements in watts. To convert watts to VA, divide the watts by the power factor (for most devices, the power factor is 0.9).

3. Add all VA values together to get a total

Then multiply this total figure by 1.25, in order to factor in a degree of future growth and / or system expansion.

4. Use the final VA figure to select a UPS

All UPS are rated using either VA or kVA figures (if over 1000VA) - always aim for around 75-85% of total UPS VA rating for most stable performance.

A typical example for a home set-up may be as follows:

PC - 200W
Monitor 1 - 25W
Monitor 2 - 25W
NAS - 30W

200 x 0.9 = 180VA
25 x 0.9 = 22.5VA
25 x 0.9 = 22.5VA
30 x 0.9 = 27VA

Total VA = 252VA
252 x 1.25 = 315VA

Suitable UPS
Minimal - 350VA
Optimal - 450VA

This example shows that a 350VA rated UPS would be adequate for this home office set-up, however a 450VA UPS would offer greater headroom and expansion potential, whilst running the UPS at around 75% of its capability.

To avoid doing these calculations manually there are online calculators provided by the leading UPS manufacturers, that either let you input the wattage figures if you have them, or select devices from a list provided. Click HERE to access the APC calculator.

Battery Runtime

This is the amount of time you want the UPS to keep equipment operating in the event of a power failure. This depends on the nature of the equipment, but in a home office scenario, runtime only needs to be for a few minutes allowing work to be saved and devices to be shut down properly. Typically, a home office UPS will have a single battery installed that is replaceable but not expandable or upgradeable - so you need to make sure you have sufficient battery runtime to perform the tasks you wish to.

Using the example above a small 350 VA rated UPS may provide enough power capacity to protect the NAS, PC and two monitors, but would only allow one minute of battery runtime. To gain more runtime you would need to select a larger UPS (perhaps a 650 VA rating) - you may only use 50% of its capability rather than 75% but the resulting runtime will be greater - several minutes allowing you to ensure things shut down without issue. Most UPS brands will provide a runtime graph, like the one below, for each model showing the expected runtime as the load increases.

Graphs like this are particularly useful if you have spare capacity on your UPS and want to know how the runtime will be affected by adding more devices or a more power-hungry PC. It is worth mentioning that if you have a NAS device or media server in your home office, then a longer runtime will be useful - this type of device may be constantly saving or backing up data and sudden interruption may cause data loss. Having ample battery time to be able to shut them down properly is invaluable in protecting your data. Finally, if your home office set-up includes numerous PCs or workstation and mission critical storage then you should consider looking at a professional UPS. It will usually mean that you will need to change your device power leads to IEC (kettle lead style) connectors rather than standard 3-pin plugs, as UPS models aimed at business use this type of power interface. However, this may be a small price to pay for the addition feature sets and extra runtime. You can learn more by reading our BUSINESS UPS BUYERS GUIDE.

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Alternatively, if you have any further questions you’d like answering about UPS, don’t hesitate to call one of our friendly advisors on 01204 474747.