Uninterruptible Power Supplies (UPS)

Uninterruptible Power Supplies (UPS) are devices that provide emergency power when the main power supply fails.

In contrast to a backup generator which takes a short while to start and take over the supply, an Uninterruptible Power Supply is able to supply power instantly (or almost instantly), so is the essential choice where PCs, servers or other critical equipment are being operated.

A UPS will also filter mains transients – this will enhance the reliability of the power supply within your equipment.

 

Factors to consider in choosing a UPS

 

Loads

• What load are you going to supply? Frequently there will be one UPS per PC / server etc. so the UPS can be rated for the exact equipment load they will be protecting.
• If the mains haven’t actually lost power but is suffering from “brown-outs” this type of UPS may switch repeatedly and rapidly from mains to backup which can cause problems for the load equipment.

 

Computers

• A desktop PC or workstation can be configured to automatically shut-down very quickly when the UPS detects loss of mains so a smaller UPS will suffice. Servers take longer to shut-down.
• PCs/workstations will typically draw ~2W when shutdown – which might be for two-thirds of the time or more. Consider that the UPS will also draw some quiescent power – anything from 2 to 20W is likely, again depending on price.
• At 10W for each UPS, this could mean you’re paying for an additional 66kWh per year per PC whilst they’re “off” – 4 stations like this is equivalent to running a typical fridge-freezer.

 

Online/ Offline

• An offline UPS will be cheaper but will take a few thousandths of a second to detect loss of mains and start its output. Most PCs will handle this okay.
• The online UPS operates its output constantly which gives no drop-outs at all to the load – but costs considerably more than offline types.
• Ferro-resonant and Line-interactive types form a good middle-ground between offline and online types but are likely to be heavier and less efficient at light loads than the other types.

 

Environment

• In a networked environment, there is no point in having workstations still running after the server has shut down.
• Where the site does have a backup generator; the UPS only needs to ride through the generator’s start-up time (with some margin) so can generally be smaller.
• If you want to have local operator intervention after the power outage and/or a manual shutdown, then the monitor will need to be supplied from the UPS too – this will affect the required UPS rating.

 

Batteries

• Batteries have limited lives and unlike in a car, where you use the battery to start the engine on a regular basis; in cheaper UPS types you won’t get any warning that the battery capacity has reduced until you need it.
• Simple battery test facilities can be specified but work by actually discharging and recharging the battery so you will have reduced protection for a while.
• More advanced Siemens testers are available which characterise the battery capacity without discharging it – but they cost considerably more.

 

Expense

• “Bells and Whistles” cost money – so only specify features you actually need.

 

Contact us to discuss your uninterruptible power supply requirements today.