At my church our server’s UPS (uninterruptible power supply) has gone belly up.

After year’s of daily abuse from the poor building power supply it has finally died. The room it is housed in (which I have noted my displeasure to the management many a time) goes from freezing cold to way too hot. Every time a light or a PC is turned on or off on the same ring main, the UPS emits a loud clunk as it kicks in and protects the server.

No more. It is dead. It has shuffled off it’s mortal coil. It has joined the choir invisible… anyway, since technology in this area has moved on apace since it was first bought how does one narrow down what we need at a price we are happy to pay?

In addressing and documenting my search I’m hoping it’ll help others of you in a similar vein. Well the first question has to be what do we want it to do? To identify that we need to understand what a UPS can do for us.

Do we want it to “condition the power” supplied to our server? Do we want it to provide continuous power for a pre-determined period of time? Do we want it to gracefully shut our server down? Do we want to do this remotely and so on? Until we can determine what we need we can’t narrow down our selections.

To my knowledge there are three basic UPS types:

Standby: or “off-line”. These generally offer simple services of surge protection and battery backup. These are inline units that sit between the power socket and the item being protected. When the voltage drops below a pre-determined level the unit ‘kicks in’ and takes over until the battery reserve is exhausted or mains power is restored. Because of the more simplistic nature of these units they tend to also be the cheapest.

Line-interactive: These are very similar to offline/standby units.The main difference is that theyprovide an automatic voltage boost when power dips without accessing the batteries. The main benefit here being longer battery life and elimination of line noise that could cause application or data errors / loss.

On-line:Needless to say this type give the highest level of protection and typically cost the most. The basic principle of these is that it takes incoming A/C power, converts it to D/C, conditions it before converting back to A/C and feeding it to the end unit. The major benefit here is stable power to the end unit dealing with common power problems and zero switching time that the others suffer from.

So, once we know what we want, we need to narrow down the market place and to my mind there has always been only the one name in server UPS supply – APC. And helpfully they also have a product selector that allows you to work your way through a tick box of what you’d like.

For what it’s worth this is the model I’ve suggested we replace it with.

So, to answer my own question… how to pick a UPS? Simple, use APC’s selector tool to determine specs of what you need… then hunt for the cheapest price, model, alternative manufacturer via Google or similar.