Having reviewed a lot of UPS ads out there, it is clear that some guidance on how to choose the most appropriate UPS System, and more importantly how to compare one UPS system against another.

Firstly, technology – generally speaking an online double conversion UPS is better than a line interactive UPS which is better than an offline UPS. There are other posts on here as to what technology does what. Secondly, line interactive systems may have sine wave inverters (best) or square wave inverters. Square waves are only recommended for computer type power supplies (and even then may be incompatible). However, they are a lot cheaper than sine wave systems.

Secondly, power capability. Power may be expressed in VA or Watts. The first thing to understand is that VA IS OBSOLETE – do NOT go by this as a comparison of UPS systems. The only true measure of a UPS capability is its WATTS rating. If a vendor doesn’t give the Watts rating it will be in most likelihood less than half -or worse- of the VA rating.
Thirdly, do not go by “typical runtime” figures. Find out how many and what type of batteries are in the unit. It is batteries that give runtime, not power rating (its just that higher powered UPS generally have more batteries than a lower rated UPS and hence give more runtime for the same load). An easy way to compare battery capacity is to multiply the number of battery blocks by the voltage rating of the battery block (usually 12V but may be 6V, or even 2V) and then multiply this by the Ampere Hour (Ah) rating of the battery. This will give a measure of Volt-Amp-Hours (VAh) which can be used to compare one unit against another to compare. For example, take a 1KVA UPS containing 2x12V 9Ah battery, this has VAh of 216. An alternative is a unit containing 3x12V 7Ah which has 252VAh thereby giving more runtime.

Finally – communications – do you need (or might you need) your UPS to be able to shut down your computer? If so, you’ll need a comms port on the UPS – and make sure it is USB, not RS232 as hardly any computers have an RS232 port these days meaning you’ll need to purchase a converter.

Follow these guidelines and you’ll be able to make an informed choice as to the best choice of UPS for you, and not be misled by technical marketing spiel.

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