How To Buy The Right UPS?

I heard from one of my colleagues in Australia that they had a power blip of a couple of hours and this was the first in the last 8 years!

Since the lockdown, majority of the workforce is working from home. In developing countries like India, grid power is not something that is guaranteed. Mostly it is attributed to the fact that the power generation is either tidal or wind and not nuclear. There are times you lose power and is a cause for discomfort.

The way out is to buy a UPS and I am not sure how many of us calculate the capacity before buying one. Most of the folks whom I work with bought a 600VA UPS. It serves their need with a decent backup time as well because the typical workforce is on a laptop and a 24-inch monitor.

First, you need to know how large the UPS capacity should be

The way to calculate your backup UPS capacity is much simpler. Let's look at it.

First, calculate your load. All electrical equipment comes with the wattage requirements written on it. You can find it on the product, the box the product came in, or even the power adaptor.

I have an office laptop that is rated for 65W.

I use a monitor from Dell, which is 24 inches wide. Its power rating is 42W max.

So total wattage is = 65 + 42 = 107W

Now convert that to VA by applying Power Factor. The general norm is 0.8

Total VA Load = 107 / 0.8 = 133.75VA

Power Factor is the efficiency quotient that tells us how efficiently is your incoming power serving the needs in VA. That gives us the capacity of the UPS that you should be buying.

Second, you need to know how long the UPS should serve when the power goes off.

You're not done yet. Now the second element is to look at how long do you need the backup. Typically I would like to have anything that would have me 15 minutes to 1 hour of backup power.

The UPS has an internal battery and the way to calculate the backup time is based on the following

Battery capacity = AH, is denoted in Ampere Hour.

The voltage of the battery = V. typically 12 V batteries.

Backup time = Voltage of the battery * Battery Capacity / Total Load.

So in this case the batteries internally are typically 7.2AH capacity.

Backup time = 12 (volt) * 7.2 (battery capacity) / 133.75 (Total Load) = 0.64 Hours, that is ~38 minutes of backup.

If you had two batteries in the UPS, that would double the backup time for the said load.

There, that should help you calculate the power needed for your equipments and the duration which it provides you the backup power.