Sizing up UPS for Dummies

Clean, Sinewave, backup Power protection over and above just power backup during rolling blackouts, is not something that’s typically discussed, but you’re going to find out why it’s essential to have.

For those of you that aren’t familiar with the term Uninterrupted Power Supply, or UPS as its commonly known, it can range from a small backup UPS with maintenance-free internal batteries, in your server room, to using a medium power size UPS or, in some cases your building basement, where you will find a large power rated UPS for building backup with large banks of VRLA (sometimes referred to as sealed) batteries.

Think of all the little black boxes that you see beneath your desk at your office, local restaurant till or your home, that all critical electronic components are plugged into; why are they there? Simple, UPS’s will keep equipment up and running when the electricity supply fails.

The questions we want to answer in this article are:

  • What it is that UPS units do?
  • What is a UPS?
  • How does a UPS work?
  • How you can choose the correct UPS, and find the one that’s right for your situation.

This article is intended for beginners, but for those of you who are technologically advanced and have a really good understanding of UPS’s this is probably just a refresher.

UPS units come in all sizes, shapes and flavours, but why don’t we start with some of the most basic needs.

What is a UPS?

A UPS by simple definition is an electronically controlled high-power-density electrical inverter device which operates in conjunction with its connected backup battery to ensure your computers or equipment are kept running even when your power goes off.

Uninterruptible Power Supply (UPS) is a device that maintains power to electronic devices, PCs, servers, network equipment, audio/video equipment and computer peripherals. During short power outages, UPS’s allows computer systems to shut down safely.

During prolonged blackouts, UPS systems also minimise the harmful effects of brownouts, overvoltages, power surges and utility switching transients (spikes and dips in power) on the connected load and data corruption.

Now that you know what a UPS system is, I think we need to talk about why you need one. For the most part, everyone’s familiar with the notorious blackouts (load shedding) and lightning surges.

How does a UPS work?

It’s imperative to understand how a UPS can save your bacon.

Let’s say you’re at home or the office and you’re working on an important spreadsheet for your boss, you’ve been at it for hours, and you’re about to save the worksheet, but the power goes out. You realise you’ve just lost most, if not all, of your work/data because your computer and or equipment was not being powered by a UPS backup system (Uninterruptible Power Supply).

If your system was connected to a capable UPS, you would at least have had the opportunity to save and or backup your work safely.

Choosing the right UPS for your situation.

Now that you know why you need a UPS let’s talk about how to choose the right one that suits your needs, determined by the equipment/load you have at your home or business.

At a minimum, you need a UPS that will bridge your load power supply of battery into the inverter feeding the load, for X amount of time plus reserves.

You also need to decide how long you would like your equipment to run after a utility supply power failure.

You will need to calculate the power your equipment is consuming by making use of a power meter, or look at the power consumption ratings on all connected hardware and add it up. These are all specified on the power supplies in VA (active power) or W (true power). You can also call the Standby Systems technical team to assist you in your load size calculations.

Whether you’re using a precise or rough method for determining the load, use the following calculation to determine your minimum required UPS rating.

There are several elements to examine when one looks at the range of UPS makes and models.

1. Sizing the UPS

  • UPS units are available in all sizes as big as 8,4 million VA and as small as 600 VA, in single or three-phase configurations.
  • Generally speaking above 10 kVA inverter rating, it is preferable to opt for a 3 phase input and 3 phase output UPS, as the imbalance on the supply of the alternator when running on the generator can have the effect of tripping or overloading on one phase of the generator.
  • Standby Systems UPS technical sales staff are ready and waiting to assist clients in comprehensive UPS system sizing and design for all types of loads from small home electronics and IT through to Large Medical, Industrial and Data Center UPS systems.

2. Battery backup

  • Although it is possible for a battery backup time of many hours, it is not the main reason why a UPS system exists.
  • A UPS system is there to filter power and bridge outages, while an alternative power source such as a generator is started or the load is powered down in a controlled manner.
  • When considering a battery, one should take into account that NO battery has an infinite life. All batteries are electrochemical factories, and all batteries will eventually fail.
  • There are many factors that affect a battery’s service life such as number of discharges, operational temperature, charging type and voltage, battery ripple current and voltage, to mention a few amongst many others
  • The most commonly used batteries designed for UPS systems are Valve regulated lead acid or VRLA, which are essentially largely maintenance-free and don’t need topping up.
  • The term deep cycle battery is widely used in the South African UPS industry, but the understanding of its design is largely not understood by the end-user.
  • A deep cycle MF battery is NOT designed as a standby UPS battery. It is an automotive technology cell with free-running electrolyte and, although it is a cheap option to use in a UPS, it comes with risks such as high hydrogen generation, under boost charging, and many others like legal aspects, health and safety, and insurance not paying out claims.
  • An SMF or MF deep cycle maintenance-free battery has a life expectancy of between 3 to 5 years after which it will need replacement.
  • There is a deep cycle VRLA battery design that employs AGM (absorbed glass matt) technology in a starved electrolyte format the same as a UPS AGM, which is used for application in solar.
  • Solar inverters operate across a huge DC supply voltage spectrum, and thus the deep cycle cell is designed to operate within this range for very long periods at a time on a repetitive basis known as cyclic use.
  • A UPS battery can operate only within a small voltage range and is required to give a high power output for much shorter periods.
  • The UPS inverter is also designed as such that it also only operates within a very small voltage range.
  • All battery systems will reach the end of life eventually, and the service life is heavily affected by installation and environment.
  • High ambients above 20 degrees C will have a significant effect on service life.
  • The number of discharges and the depth of those discharges will also weigh heavily on a battery’s service life.
  • Generally, there are two types of VRLA UPS batteries separated by what is called the design life; i.e. 3 to 5 years and 10 years.
  • Many manufacturers are claiming all sorts of more extended and better service life, but in practice, the UPS user will achieve life expectancies of approximately 3 years and 6 to 8 years for these two design life products.
  • It is quite possible for a 10-year design life cell to exceed 10 years if the environment and operational conditions and usage are right, but under the rolling blackout conditions in South Africa, it is highly unlikely.
  • In conclusion the only way for a user to have unlimited backup time on a daily backup basis that is uninterrupted during rolling blackouts is to have a UPS with a short backup battery time and a generator to bridge out the many hours of power failures using a fuel power source that is easily topped up and much less capital outlay in the service life.

3. Rolling blackout battery banks

  • A battery that is discharged for 4 hours every day will not last more than about 1 year, and then it will need replacement; that is assuming it is possible to get 80% of its capacity out in 4 hours, which in the case of VRLA or MF deep cycle is impossible.
  • If a 10 year design life battery is sized correctly for only 20% capacity removal every day, then it will last for about 3 years but that is if the person who sizes the battery knows what to do, technically.
  • It is quite possible for a UPS that is X kVA to deliver 4 hours standby using two massively differently sized batteries with different costs.
  • This is because the cheap version will discharge 80%, i.e. give out 80% of available capacity while the expensive version will only give out 20% of its available capacity.
  • The difference is that due to charge limitations in lead-acid batteries or VRLA cells or even SMF type automotive batteries, there is a manufacturers recharge current limit as to the amount of capacity you can put back into the battery in a 20 hour period under rolling blackout conditions, which if the limit is exceeded, the cell will be permanently damaged.
  • So in the case of the small, cheap battery, it can give out a lot of capacity in 4 hours, but it can not get that capacity back in 20 hours, so it will not be fully charged in 20 hours resulting in the user blaming the battery for “not working.”