UPS Buyer’s Guide

People are often unsure about which UPS to buy that will best suit their individual needs and their budget so that they don’t over-buy or under-buy, but rather make the right purchase first time round. For this reason it is very important to have a good understanding of the different UPS backup technologies that are available from our UPS product range.?

How is a UPS system rated?

UPS systems are mostly rated in VA. The VA rating stands for Volt Ampere and is calculated by multiplying the Amps rating of your appliances, which is normally specified on the rating plate. VA is a measurement of apparent power. The rating of all UPS systems refer to the inverter rating. All UPS inverters, although rated in VA, are subject to a power factor rating. If a 1000 VA UPS is rated at a 0.6 power factor then it is a 1000 VA x 0,6 pf = 600 watt UPS, whereas if a 1000 VA UPS is rated at 0.8 lag power factor then it is 1000 VA x 0,8 = 800 watts. Thus the 800 watt UPS can deliver more power, even though they both have the same VA rating. (Watts is the meaning of true power and is the VA x the power factor for most general UPS loads). If you have a highly specialised load then it is best to talk first with your Standby Systems UPS technical sales consultant. The best way to compare when it comes to a UPS inverter rating is to compare the cost per watt in ZAR and NOT cost per VA in ZAR.

For example:

The 1000 VA UPS example discussed above could be either a 600 watt or 800 watt unit, so let’s look at actual value for money:

A)???????????????????1000 VA 0,6 pf (600 watt) UPS??????????R 100.00 and

B)????????????????????1000 VA 0,8 pf (800 watt) UPS ?????????R 115.00

?At first, it looks like the 1000 VA option A is the best and cheapest priced UPS at R 100.00 for 1000 VA, but if you look at the true power, which is what counts, then 600 Watts/R100 = 6 Watts per rand in cost while doing the same sum with option B, 800 watts/115 = 6,95 watts per rand. In actual fact option B is the best value for money as you get more watts for your rand in the same VA rating UPS.

?Many unsuspecting UPS purchases are done comparing only VA price to Rand cost while in actual fact the “bargain” you bought is the most expensive option by far. Don’t get caught out with this.

?Now that you understand about the rating of a UPS and what is the best choice in terms of value for your hard earned cash it’s important to understand how to choose the right size UPS by sizing your load. To buy a UPS system that only works at 5% of the full inverter load capacity is a big waste of money and energy losses.?

Calculating the load

You can obtain any device’s power consumption on the rating plate, on the power supply, or from the manual. The power rating will either state VA or W or volts (V) AC and?amps (I) AC. For a load that states V and A simply multiply V x |A which will give you the apparent power VA rating of that device. Once you have everything worked out in VA, write a list of all the ratings in VA along with the loads in watts. For simplicity sake add the VA and watts together and assume this is the total UPS inverter rating you will be looking for. Take the calculated UPS inverter rating and multiply it by 1,3 to allow for load growth and some start-up/peak power draw devices.?

For example:

Device 1?????????Rating plate says 220 V or Volts or VAC and 3 A or amps. Therefore the required rating = V x A = 220 V x A = 660?

Device 2?????????Rating plate says?100 VA. Therefore the required UPS VA rating = 100?

Device 3?????????Rating plate says 240 watts or 240 W. Therefore the VA rating = 240

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Add them all up: 660 + 100 + 240 = 1000.

Allow for load growth and peak loads: 1000 x 1,3 = 1300

You need to purchase a UPS capable of supplying a minimum of 1300 VA.?

Deciding on the best back-up time

The next step would be to decide what battery backup time you need when the lights go out.?Although everyone will commonly ask for 4 hours or more backup time, it is not is not so simple.?

?Remember – batteries cost big money and they don’t last forever. The bigger the battery backup the bigger your headaches and total cost of ownership long-term.

Realistically, when it comes to choosing a battery backup time, do not expect unlimited battery backup unless you have the cheque book to match your requirements for many years to come. The best battery selection for a UPS application is 30-minutes or less. If you want to run for longer periods then your best bet is to use the UPS battery to cover the time from when the power fails until a generator backup is started and feeds the UPS.?

Long runtime battery back-up

If you do decide that you want a long battery backup runtime with your UPS inverter then make sure that you are buying a UPS with an appropriately rated rectifier (battery charger) to charge the battery. For easy reference, when you choose a long runtime battery backup you will require a UPS that will give you a minimum of 15% of the total battery ampere hour rating or AH rating. If your UPS supplier is offering you 4 strings of 100 AH batteries on your UPS you will need 15% of 4 x 100 = 15% of 400 = 60. In this example, your UPS rectifier should be able to give you a minimum battery recharge current of 60 amps while still being able to supply the inverter’s full load rating of the connected load. Additional to the recharge current you need to ensure that the UPS rectifier can give you sufficient voltage to charge properly. When a battery is subjected to rolling blackouts, it will need to be recharged at a higher than normal voltage rating. You need to ensure that the UPS rectifier can charge the battery at 14,5 volts per 12 volt battery block for such a cyclic application.

The next headache when it comes to long battery backup times is that your battery, under rolling blackout situations, will only manage about 300 discharges (depending on how your UPS supplier has sized the battery) before it needs replacement. When you have regular discharges on the battery for long periods you will need to purchase a new battery backup within two years. In 10 years of using your UPS inverter system you could change your battery banks as much as 5 or more times, which is extremely expensive.?

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Understanding backup battery warranties and terms of use

There are other battery types and technologies on the market that claim more cycling, long service life etc., but remember the golden rule when buying batteries: the life expectancy or rating means nothing; it is just open marketing statements. All battery warranty in terms of full replacement is 12 months or in some cases 2 years, but the terms and conditions attached thereto make the full replacement warranty even more grey than that; with so many loopholes it’s impossible to prove a product or mature failure.

?When choosing a battery backup system it is essential you choose a well-known brand such as ELITE, Enersys, CSB, |Vision, Chloride/Exide from FNB. Use a UPS supplier with good technical knowledge in order to size your backup battery correctly as well as supply you with the right technology product, personalised for your application, along with your UPS system.

Lastly, currently the only battery technology that is 100% recyclable in Africa is the lead-acid battery technology. Any other battery technology will require expensive export costs to send it back overseas for recycling and most of these technologies are not 100% recyclable. Choose a green solution not another item to dump in Africa. Choose a lead acid VRLA backup battery with a good reputation like the ELI|TE or Enersys.

Once you have decided on what battery backup you want, it is important to understand the different UPS technologies available in the marketplace and what is best?suited to your actual needs.

Consider other factors when selecting your UPS

Other factors that are important when selecting a UPS are:

·??????Operational environment

·??????Communication interfaces

·??????Redundancy

·??????Preventative maintenance and afterhours backup

Operational Environment

One of the biggest killers of a battery is the operational temperature it is subjected to. The ideal operational environment temperature for a UPS battery is around 20 to 25 degrees Celsius. If the UPS backup battery is housed in a hot environment, like in a cabinet that is exposed to the sun, or in a room with no ventilation, the UPS backup battery could start dying in as little as 3 to 6 months.

?Although an AROS RIELLO UPS can operate at temperatures of up to 40 degrees Celsius, it is important to note that long term operation at such high temperatures will reduce electronic component life expectancy just like a normal PC would be affected. The best practice is to not subject your UPS system to anything more than you would any IT load. Then your UPS should run, trouble free, and the battery should last for some years to come.

Communication interfaces

If you wish to be able to interrogate your UPS system and if you want to shut down your connected inverter loads in a controlled manner when the power goes off there are many communication options available; not only for IT, but also for industrial product communication highways such as ModBus, JBus and interface to your building management systems in any size building, from small to large data centres or factories. This software is also capable of sending various types of communication for a wide range of UPS conditions that are easily selected or deselected.

Redundancy

If your UPS backup power application is highly critical because:

?1)????Human life depends on power availability such as life support systems, ventilation systems, industrial and power plant control systems or emergency backup systems, etc.

2)????Loss of power to the UPS load will result in large scale loss of money for a business.

3)????Loss of power requires many hours or days of cleaning or restart procedures, for example in plants.

4)????Loss of power in IT applications is not negotiable with 100% uptime needed.

?Then you would want to consider various UPS redundancy options including parallel redundant or N+1 or N+X applications such as is required in the various tier data centres. A combination of UPS systems with Static transfer switches or STS as they are known is also a viable option when the critical load only has one power supply in it.

?Should you wish more in-depth information on UPS redundancy options, Standby Systems’ Technical sales Engineers are available for further discussions and proposals.

Preventative maintenance and afterhours backup

Lastly, an important consideration when choosing your UPS is to make use of a reliable, local supplier that carries the correct spares and technical knowledge to be able to offer 24/7 support in case of emergencies. In the case of corporate users, you need to find someone who offers country wide backup.

An important question to consider:

What is the cost of loss to you or your business if your critical load is damaged by bad power or power failures versus buying the best UPS solution available?

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