Choosing the right Uninterruptible Power Supply (UPS). A Low Down

An Uninterruptible Power Supply (UPS) is a standby power arrangement system. UPS can be used for providing backup power to any electrical equipment, but mostly they are used as a standby power arrangement for PCs. In places where power outages are frequent and supply is not guaranteed UPS can also be used for running electrical equipment like fans, lights, TV sets etc. A UPS is also used in medical and telecommunication equipment or places in the industry where power outages can result in loss of life or can cause financial losses. A UPS comprises of battery system which stores electric charge. It also has a charging system to charge these batteries and means of converting the stored Direct Current (DC) to Alternating Current (AC). Modern UPS are intelligent devices and can manage the charging system, that is they shut off the electric power to the batteries when they are fully charged and turn off the UPS when the batteries are close to being discharged completely, thus preventing permanent damage to the batteries.

Types of UPS.Mainly there are three types of a UPS.

  • Off Line UPS. A UPS which has to be turned on when main electricity fails. These are almost non-existent today because they are based on old technology and are not automatic.

  • Line Interactive UPS. A Line Interactive UPS is the most common category of UPS today. Line Interactive UPS keep on sensing the electricity (mains) and on failure of power automatically switch to back up mode, thus providing power to the system.

  • Online UPS. Online UPS is the most expensive category of UPS and are normally used in medical equipment so that clean uninterrupted power is available at all times to life saving equipment. Today we are mainly discussing the Line Interactive UPS category.

How to choose a UPS.Choosing the right UPS can be tricky. But by reading this guide and following the steps mentioned you will not only be able to make calculations based on your requirement but also but the right category and type of UPS.

Define your need.This is the most important step in the whole process. Electricity is always measured in Watts. A Watt is the unit of power. Never mind if you are not a techie I will explain the whole thing in easy to understand words. Say for instance you want to buy a UPS for your PC and printer. So first of all we calculate the power required or the load. Just read the manual of your PC, monitor and printer to find out how much power it requires to work on. The thing to see is how much current does it need. For example you monitor says it requires 1.2 amperes of current, you PC requires 1.3 amperes and your printer requires 1.1 amperes.

Some Calculations Required. (Doesn’t matter if you sunk your Arithmetic course in high school this is simple addition and multiplication Smile)

So total amperes is 1.2 + 1.3 + 1.1 = 3.6 amperes, we round it off to 4 amperes.

Now remember watts = amperes x volts

So, here watts = 4 x 220 = 880 Watts (We round it off to 900 Watts. In case you are wondering what is 220? well this is the volts. Depending on your area and country this can vary from 100 Volts to 220 Volts. This normally written as VAC (Volts Alternating Current). If you are not sure ask your electric company. Or you can visit these pages or see it on Wikipedia.

Now we know how much powerful UPS is required, it has to be at least 900 Watts. Normally UPS manufacturers make UPS in multiples of 500 Watts, so you can expect 500, 1000, 1500 Watts etc. It is always better to go for a little higher spec than the requirement. So in this case we will go for a 1000 Watts UPS. (Also called 1 KVA)

How much Back Up Time do you need?The amount of time for which your UPS will provide power depends upon the battery being used. Normally a sealed Lead Acid battery is used in a UPS. So it does not require to be maintained.  If you live in an area where power outages are not quite frequent and you need the UPS just to save your data then a small battery will suffice. But in case you live in an area where power outages are for hours then you need a powerful battery. Battery power is measured in Ampere Hours (AH).

So if a batter has an AH capacity of 10 it can work in the following way.

  • For 10 hours if  the load is 1 ampere.
  • For 5 hours if the load is 2 amperes.

Some Calculations Required (Again).

The AH capacity formula is : AH = Amperes x Hours (Time)

So a 10 AH battery can work in any combination till the time the result is 10.

2 x 5 = 10, 2.5 x 4= 10, 10 x 1 =10 etc

In our case the total amperes is 4 and if we need the whole system to work for say 3 hours then the battery required will be

AH = Amperes x Time (In Hours)= 4 x 3 = 12 Ah, So you need a 12 Ah battery to make the whole system comprising of a PC (monitor included) and printer to work for 3 hours.

Some Important Tips.

  • Go a name brand like APC, Eaton etc.
  • Always ask your vendor if the UPS comes with a warranty.
  • Going for a little expensive brand is always better as the benefits are more in terms of value for money.

  • In case you need more back up time ask the vendor if he can fit an external battery. Some UPS brands cannot be fitted with external batteries.

  • Always read the instruction manual before operating or installing a UPS. This holds true for any electrical device.


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