UPS Batteries: Questions and Answers

1. What does a UPS battery life of 3, 5, or 10 years mean?

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3, 5, or 10 years when referring to a UPS battery is a general term used for high specification EUROBATT and IEC compliant lead-acid batteries regarding their in-service life-expectancy when they are designed and built for use in Riello UPS systems. Batteries compliant with these standards guarantee the user peace of mind. Although UPS backup batteries are generally more costly, they are of much higher build quality, better performing, and have a longer design life than standard batteries.

These compliant batteries have a design life of 12 to 15 years, are built in flame-retardant PVC casings with threaded Cu inserts for the main terminals, and are most popular in high spec UPS installations where reliability is a major factor.

2. How do I size a UPS correctly?

There are many things that affect the sizing of a UPS backup system. These include:

• The accumulated overall inverter load to be connected.
• The type of loads to be connected to the inverter.
• The type of backup, i.e., a short duration of 5 to 30 minutes just to allow time to safely shut down the load when the power goes off, or long battery backup to carry the load through load shedding.
• If the load is highly critical, then one may want to consider a parallel redundant UPS plant so that if one UPS should fail, the load will still be protected by the other parallel UPSs.

It is very important to choose the right UPS technology for the load you wish to connect. Different technology UPS systems offer different levels of load support and protection – along with higher pricing as the technology gets better.

UPS technologies commonly available nowadays are:

• Off-line UPS: offering least load protection overall and only short battery backup of 5 to 30 minutes, inverter load dependent.
• Line-interactive UPS: offering more load protection. Often with built-in Automatic Voltage Regulator (AVR), it features quicker switch-on times and is also suited to short-duration load backup on power failures of 5 to 30 minutes, inverter load dependent.
• Online double-conversion UPS offering full load protection, no switch-on time, and available for short battery backup or long battery backup of several hours.

Another important factor is to ensure that the UPS is not sized too large for the actual connected load, as a UPS running at 25 to 50% load is very inefficient and has high running costs due to high inefficiencies at low loads. Ideally, the inverter should be running between 60 and 75% of the actual power rating.

Suppose you're not sure what size UPS you need. In that case, Standby Systems have a highly competent team of UPS technical sales engineers, specializing in UPS systems for all applications, from small 1-phase Riello UPS units for your home or small office to large 3-phase UPS power plants. Our specialists will visit your site free of charge to assist in your UPS sizing. Contact us or email us, and we will send a free UPS load calculator. Using the calculator, you can select the loads you want to connect to your UPS to determine the UPS size you need.

3. What is galvanic isolation of a UPS inverter?

Galvanic isolation is the use of a double-wound transformer, generally on the UPS output inverter, to isolate the load from the UPS battery power. Should an inverter short-circuit, there is a chance that the load will be subjected to high DC (battery) power, which will certainly damage any sensitive load connected to the inverter. The isolation transformer prevents the DC from doing this and acts like a one-way valve allowing only AC power through it.

Galvanically isolated UPS systems, like the Riello MPT, MHT, and MHE ranges, are widely used when high-demanding power is required by the inverter load, such as mixed building loads, motors, air conditioners, medical imaging loads, and other industrial loads like plasma cutting machines, etc. The inverter output transformer makes the UPS far less susceptible to these harsh loads and is a more reliable solution and lower cost, long term, than a transformer-free UPS inverter.

4. What is harmonic filtering?

Harmonic filtering is necessary for large 3-phase UPS plants to limit the amount of "electrical noise" that the UPS rectifier generates back into the ESKOM power grid. This noise can be so bad that it will prevent a building's power factor correction equipment from working, which results in huge unnecessary electricity costs.

This noise can penetrate other equipment connected to the building's supply and affect its operation; causing overheating of UPS supply cables and UPS supply distribution boards. Its effects cannot be seen with the eye, but they are nasty overall and easily avoided using a UPS with a total harmonic current distortion back into mains of less than 3%. In years gone by, this was achieved by using a 12 pulse UPS rectifier, but this has been replaced with a far more effective component, namely, an IGBT rectifier.

5. What does battery backup mean in a UPS?

Battery autonomy or battery backup in a Riello UPS system refers to the amount of time the load will continue to run even when the ESKOM supply goes off. The longer the battery backup to the UPS inverter, the higher the cost. Ideally, if one experiences frequent power failures every day or a few times a week, then the UPS should be used in conjunction with a generator so that the battery backup is only for a few short minutes while the generator starts, i.e., the UPS is only there to bridge the gap in power, not supply power for hours.

If it is not possible to run a generator in conjunction with a UPS, then a long battery backup will have to be considered. This is an expensive and limited option, with many long-term costs, because:

1. A normal, affordable UPS battery can only undergo about 200 to 300 full discharges.
2. A long battery backup system requires a lot of space.
3. Big battery banks are more of a fire risk.
4. UPS Batteries must be recyclable in South Africa, so use only lead-acid products.
5. UPS Batteries require replacement every 3 to 8 years usage dependent, leading to a high total cost of ownership.

6. What is the point of using a UPS or uninterruptible power supply anyway?

An uninterruptible power supply, also known as a UPS system, is primarily aimed for use in protecting sensitive IT/electronic and other connected inverter loads from the following issues:

• Power failures
• Brownouts or short loss of power
• High spikes or transients caused by lightning and the switching of high voltage switches on the ESKOM grid
• General bad power as experienced in areas near heavy industry, such as arc furnaces

The UPS acts as a filter and prevents the connected inverter load from "seeing" the bad power supply while using the battery backup power to manage situations of power supply loss, ensuring the load continues running unhindered.

A UPS thus protects its connected inverter loads from bad power or loss of power supply. It prevents software corruption, data loss, injuries in production, loss of production, loss of time, equipment damage, and many other issues.

7. Can I use a UPS for an air conditioner or motor supply?

An air conditioner or any motor with a start/stop load is a very harsh load that distorts the mains supply due to its very high current demands on start-up and often regeneration of power back into the mains supply when it switches off – also called a regen load. These high start-up currents normally exceed the UPS inverter's ability because although it can cater for peak loads, it can only supply a certain amount of peak inverter load for a very limited time.

For this reason, it is not advisable to put an air conditioner or start/stop motor load into a UPS. One way around this is to put a variable speed drive between the UPS and the motor load, which will soft-start the inverter and protect it. Alternatively, a generator is the preferred supply option for these types of loads.

8. What is UPS load shedding and how can I lengthen my available battery backup time on my UPS inverter?

In South Africa, we have become used to the words "load shedding", "inverters", "backup power", "solar", and "off-grid".

What does the word "load shedding" actually mean in the context of UPS systems or UPS plants? Well, the answer is simple. A UPS inverter will usually have several loads connected to it that need clean power filtering and reliable inverter power backup when the lights go out.

In most cases, many of these loads do not necessarily need to be kept running; they just need to be protected from bad power or sudden loss of power. Under power failure conditions, these loads can be shut down in a controlled manner, either manually or via the Riello Powershield and Watch and Save software (which is freely available), or a UPS network interface or SNMP card, which is optional on purchase or can be retrofitted. This software is a powerful UPS tool that can be easily and safely used to power down less critical loads during a power failure in a controlled manner, thus increasing available battery backup time for the inverter loads that must run continuously. This process is known as UPS load shedding to increase available battery backup time.

9. What does an automatic transfer switch (ATS) do for me, and how does it work?

An ATS is a device that allows for 2 input supplies and 1 output supply. In UPS systems smaller than 10 kVA, the ATS is generally a 19-inch rackmount device with 2 sources of input, i.e., UPS 1 inverter connected to input 1 and a UPS 2 inverter connected to input 2. These devices have several IEC plug outlets to plug loads into. With IT and Datacenter equipment being highly critical but often only having one power supply, the ATS at least allows the equipment connected to its output to have two UPS supply sources in case one of the UPSs should fail.

Another form of ATS is called a Static Transfer Switch (STS). It is far more advanced than the ATS technically and designed for use in higher-power single- and three-phase applications, usually in conjunction with a UPS feed to input A and another UPS feed to input B.

10. What does transformer-based UPS inverter mean?

Since UPS systems were first designed and built, they were always made with an inverter output transformer. This had two functions:

1. The transformer was used to step up the inverter output voltage to 220/400 volts supply for what we use here in South Africa.
2. The transformer galvanically isolated the load from the UPS battery, thereby protecting it.

Nowadays, transformer-based UPS like the Riello MPT, MHT, and MHE have a third positive effect in that they create a new neutral for the critical connected inverter load, bringing the neutral much closer to the load. This drastically reduces the effect bad neutrals can have on the functionality of critical data center, IT, and software loads.

With the Riello MHE UPS, there is the added advantage that this UPS system is extremely efficient and has low losses, with a small footprint making it ideal for use in Datacenters where space is expensive and precious.

All Riello transformer-based UPS systems can be installed up against the wall, making them more space-efficient. They also only require front access for servicing and 500mm clearance above the top of the UPS for fan airflow and cooling.

11. What does transformerless or transformer-free UPS inverter mean?

In more recent years, transformerless or transformer-free UPS systems have been developed, with most manufacturers moving away from transformer-based UPS systems. This newer technology is far cheaper to produce and thus more competitive. This technology is also more efficient and requires a smaller footprint.

However, in most cases, the smaller footprint doesn't necessarily mean less room space use, as almost all UPS systems with transformerless technology require front, side, and back access, plus rear clearance for fans exhausting hot air. Essentially, they take up less floor square meterage but need more room area around them.

They are very efficient, which is very important in the green energy UPS world we live in. Still, they can easily and more effectively be replaced in high power ranges with more reliable and robust transformer-based Riello MHE flagship products, which give the user peace of mind, offering both high reliability with ultra-high efficiencies – the best of both technologies in one.

In the field, transformer-based UPS units tend to be far more reliable than transformerless UPS units. They are generally only used when connected to inverter loads that are highly demanding and harsh on the inverter. They are more costly, so the cheaper alternative is generally used for most UPS backup applications.

12. What is the difference between critical and non-critical UPS inverter loads?

To begin with, it is necessary to put together a list of all the loads that need to be protected by the UPS from power failures and bad power supply from the grid. This list of UPS inverter loads is known as the critical loads, and it is essential they have inverter and battery backup when the power fails. It is important to remember that UPS and battery backup are ‘essential components’, so it is important to be 100% sure the selected critical inverter loads are the absolute minimum. No luxuries are allowed for in the sizing. Any other load that is not required when the power fails is a non-critical load.

13. Calculating the power draw of the critical UPS loads

The total power draw of the selected critical loads is obtained by making a list of the power rating of each piece of equipment. This detail can be obtained from the rating plate, normally at the rear or under the device, or off the power supply feeding it. Once you have the list, add it all together, and that will be the total power draw to select on the UPS. If you have a problem with sizing, you can email Shaun and request a UPS sizing calculator to assist you in your sizing.

14. How to select the right UPS size?

Once you have the total power draw added in watts, you can select the UPS size accordingly. It is important to allow 30% on top of the calculated power draw to accommodate when loads start up, resulting in higher than normal inrush currents on the UPS inverter. If the total power draw is in watts, you need to divide this by 0.7 to get to the VA size, which is what UPS units are generally rated in. A UPS up to 3 kVA is a plug-and-play device and doesn’t require installation. Units of 4 kVA and upwards require an electrician to hard-wire the UPS into your building.

15. What UPS inverter loads have the potential to cause problems with the UPS’s operation?

Some types of loads have very high inrush currents on startup or just draw far more power than other items the same size, for example:

• Laser printers
• Air conditioners and pumps
• Lighting including LED lighting, which draws what is known as a leading power factor
• Certain types of servers such as blade servers
• Motor loads

If connected to a UPS, these kinds of loads will cause it to go to bypass continuously, giving constant alarms. They will also affect inverter operation while under power failure conditions during battery discharges. The best way to cater for such loads is to either leave them off the UPS completely or calculate their peak instantaneous power draw on startup and include this in your sizing. This peak is often not normally stated on the device power rating and must be obtained from the manufacturer, or you can contact Shaun for assistance or email us to arrange a site visit by a technical sales engineer from Standby Systems.

16. What is the battery backup or run-time on a Riello UPS?

The battery backup time is the period of time for which you need to keep your loads on inverter battery backup, up and running. This could be for several hours to bridge an entire power outage or for the time it takes for your backup generator to start up and take the load, which is normally less than 5 minutes. If the load doesn’t have to run all the time in a power outage, but just for long enough to allow time to shut down properly, a backup time of 10 to 30 minutes is generally used. The backup time sized at full UPS inverter load is ironically affected positively if the actual running loads are reduced to a minimum under a power failure scenario. Load reduction results in a non-linear battery discharge, so for example, a UPS battery sized for 5 minutes backup at full inverter load will get far more than 10 minutes backup at 50% inverter load.

17. Why does the operational ambient temperature affect my UPS batteries and what does it do to them?

UPS Sealed valve-regulated lead-acid batteries, also known as VRLA batteries, are high rate batteries that are an electrochemical device. ELITE brand is an example. All batteries contain a liquid known as electrolyte. A UPS battery uses a technology called starved electrolyte, whereby the amount of liquid inside is minimal, and therefore it is not considered a spillable device. A UPS battery is designed to run at an ambient temperature of between 20 and 25 degrees Celsius over its service life. When operated at temperatures higher than 25 degrees Celsius, the electrolyte will evaporate at an accelerated rate. This causes a pressure build-up inside the battery, forcing the emergency valve to open and purge the gas. The loss of gas means a loss of liquid in the battery, and the battery will dry out much faster than normal, causing premature failure. UPS batteries operated at over 30 degrees Celsius will achieve less than half their expected service life.

18. What does an automatic-voltage-regulator do for me?

An automatic-voltage-regulator (AVR) device,