Four steps to consider before buying a UPS

Updated: Mar 8, 2021

Investing in a power back-up is one of the most important aspects in today's homes and offices. Investing in the right technology and capacity of the UPS is even more vital to derive the best value on your investment. I know of many customers who have invested in a UPS and within a few months have found it either undersized or oversized and in some case have realised it not necessary and hence wanted to dispose it. In this post I will give you important information on points to consider before you buy a UPS.

Understand your Power: The first step is to study the kind of power you are being supplied by the utility company or by the community service provider. Also consider what kind of power you are likely to receive in the next 4 - 5 yrs. It is important to understand what kind of power you are receiving. Is it 3 Phase / 1 Phase? How many different circuits you have and what appliance / device does each circuit powerup. Study the kind of power disturbances your premises is experiencing. Look at typical incoming voltage and if there is any noticable fluctuations. Voltages normally vary during different parts of the day. If you are close to industrial areas, you may witness lower voltages during the day and possibly higher voltages in the evenings and nights. In many localities, since the usage in the evening is high and due to transformer overloading, people may experience a drop in voltage. Even if you have a Diesel Generator back-up in your community, check the power quality when the generator is supplying power. Now that you know the kind of power outages, power disturbances and the power back-up you have, you are equipped to make an informed decision of whether you need a UPS and /or a power conditioner or it may even be that you don't need one.

Find out UPS capacity you need: If you have decided to go for a UPS, the next step is to identify the devices and appliances which need power back-up or power conditioning or both. Group them together and note down the maximum and normal power consumption of these loads. Most of the appliances and devices have this information printed on the specification labels or in the user manual. Next it is time to analyse the main power distribution panel in your house or office which will have multiple MCBs catering to specific circuits. Note down which MCB caters to which circuit and appliances / devices. When you do this, you will be able to know which circuit you need the UPS to support. You will get a total load power consumption in Watts which the UPS needs to support and consequently the capacity of the UPS you need. For example, if the load power consumption which needs to be supported works out to 1000 Watts add 30% to it to arrive at minimum UPS capacity (considering a normal power factor of 70%) of 1.3 KVA. You can now look for a UPS of this capacity or more in the market. Generally the nearest capacity available in market would be 1.4 KVA / 1.5 KVA. You can consider these.

Calculate the Battery Capacity: Batteries are expensive consumables and they lose life every time they discharge power. Hence the size of battery you choose should be such that it is capable to give the optimum back-up and last for about 4 yrs. To do this firstly you should arrive at the desired back-up for your above loads, keep in mind the kind of power outages which is prevalent in your area. If you live in the heart of Bangalore city the back-up you should plan is 3 Hrs, which is normally a common assumption by solutions provider based on historical power outage trends.

Next you should be aware of the number of batteries the UPS needs. Since commonly available batteries designed for UPS are 12Vdc, you will require 1 battery if the UPS nominal dc Voltage is 12Vdc. you will require 2 battery if the dc voltage of the UPS is 24 Vdc, 3 for 36Vdc, 4 for 48Vdc and so on. In the above example a 1.4KVA / 1.5KVA is 24Vdc system and hence requires 2 batteries in series. You can arrive at the battery capacity by using this very simple formula.

Each Battery capacity ( AH) = Load ( Watts) x 1.6 ( factoring efficiency losses) x Back-up ( Hrs)


In the above case, the capacity required is (1000 Watts x 1.6 x 3 Hrs) / 24Vdc = 200AH

Hence you will require Two batteries of 200AH to support a load of 1000 Watts for 3 Hrs.

Is your site prepared for UPS: Now that you know what capacity of UPS and batteries you need to invest, the next step will be to check if your house or office is wired for UPS and is there is a convenient place where you can install the UPS.

The UPS is a power supplying device. It needs power for its working and the output from it needs to be connected to the loads. Since the UPS needs to cater to different circuits, the output from the UPS should be wired to the various MCBs catering to the identified circuits. This is a pre-requisite for the UPS to work. Any qualified electrician will be able to set it up for you. Most houses and offices are equipped with a UPS circuit pre-installed with a UPS input and output points provisioned. If it is already pre-installed, you should check if it is catering to the desired circuits. If the pre-installed UPS circuit is covering more than the desired circuits, you should get the modification done through a qualified electrician to isolate it from these undesired circuits. If this is not done, you will have to rework on the capacity of the UPS on the new load requirements based on all the appliances devices which is connected to the UPS circuit.

The UPS needs proper ventilated area which is away from direct sunlight and excess humidity. Also since it is bulky and heavy it should be installed in a place where the platform can support the weight of the UPS and batteries and is convenient from a maintenance perspective.

The above 4 recommended steps will enable you to male an informed buying decision and plan your spend on this investment. Wishing you all the very best.

I have tried to provide information as simple as possible to benefit all the readers. Feel free to leave your questions, comments or suggestion on this topic. Thank you for reading.

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