Backup Power Systems: VRLA, VLA, Lithium-ion Batteries Overview and Working

Understanding your UPS battery can help you save time and money, prolong its life, and avoid expensive downtime. It is common knowledge that a UPS’s battery is its most delicate component. In actuality, a major factor in load loss is battery failure. Your UPS batteries’ lifespan will be extended by knowing how to maintain and manage them, which will also save you time and possible trouble in the future.

Overview of UPS batteries

Valve-regulated lead-acid (VRLA), often referred to as sealed or maintenance-free lithium-ion batteries and vented lead-acid (VLA) batteries are the three major types of batteries used in UPSs (also called flooded-cell). Although they often cost less upfront than VLA batteries, VRLA batteries typically only last five years on average. Flooded-cell batteries have a lifespan of up to 20 years but require more complex maintenance.

VRLA

The typical container used to seal VRLA batteries is polypropylene plastic. They were created because they don’t contain any sloshing acid that could spill or drop out if handled violently or turned upside down. The mechanism of gas release is referred to as valve regulated. The valve will vent when it reaches a particular pressure if the gas pressure inside the battery rises too much. Hydrogen is typically released while a lead-acid battery is being charged. The hydrogen escapes from a vented battery and into the atmosphere. In a VRLA battery, internal hydrogen and oxygen are recombined to reduce water loss. Nearly all of the hydrogen and oxygen are recombined in float circumstances.

Re-sealable valves only release non-recombined gases when a certain pressure is reached. The speed at which oxygen diffuses from the positive plate to the negative plate and eventually forms water separates a VRLA battery from a flooded-cell battery. This pace is far faster than a flooded-cell battery by many orders of magnitude. Water cannot be added, thus its recombination is essential to a battery’s life and health. The battery life is impacted by any element that accelerates the rate of evaporation or water loss, such as ambient temperature and heat generated by the charging current.

VLA

Batteries called VLA or flooded cells have heavy lead-based plates that are submerged in an acid electrolyte. This is a very dependable design; failures typically don’t happen until halfway through their 20-year pro-rated life, and when they do, a short circuit is most frequently the cause. Because each shorted cell only has a very little impact on the total reserve time, the problem is not extremely urgent. However, flooded-cell batteries still have drawbacks despite their high level of dependability and long lifespan. To use them, additional safety precautions and a roomy separate battery room are needed. Although there are various types of UPS batteries, both need to be monitored and maintained to ensure optimal life and system uptime.

Lithium-ion

For UPS applications, lithium-based batteries offer several important advantages over other DC storage methods. The technology is seen as being appropriate for critical power backup because it has become mature in heavy-duty applications like electric automobiles. The main advantages of lithium-ion batteries are their small size and lightweight, but they also include extra characteristics such as integrated battery management (not only monitoring), which makes them a desirable replacement for conventional batteries. Additionally, they can be used in non-traditional UPS applications including grid sharing, peak shaving, and industrial or process control assistance because of their high cycle count (charge-discharge cycles) and quicker recharge durations compared to lead batteries.

Each battery has a battery management system installed in it, along with a system-level master controller. It controls the balance of the charge current, voltage, and cell voltage while making any required modifications to prevent overheating. The management system will autonomously disconnect the battery or string if temperatures exceed safe levels using several different methods. It will also alert the user via the battery cabinet monitor and an alarm on the UPS. Overall, a lithium-ion battery system offers a cheaper total cost of ownership (TCO) due to comparable Capex costs, savings on Opex due to a longer replacement interval, and operational flexibility at higher ambient temperatures.

Battery configuration and power

You don’t use a single cell at a time in the majority of UPSs. Typically, they are connected in series to create greater voltages or in parallel to provide higher currents. The voltages increase when the arrangement is serial. In a parallel configuration, the currents combine. Batteries aren’t exactly linear, either, as the two pictures to the right show. A 500-milliamp-hour battery, for instance, cannot create 30,000 milliamps in one second because its chemical reactions cannot occur that quickly. All batteries have the maximum current they can produce. It’s crucial to be aware that batteries can generate a lot of heat at higher current levels, which wastes some of their capacity.

UPS batteries are electrochemical components, the same as all other batteries. In a UPS, the electrolyte is diluted sulfuric acid, and the electrodes are grids of lead that contain lead oxides that alter composition while charging and discharging. In other words, they are made up of parts that interact to produce DC electrical current.

These elements include:

• The electrolyte, which is immobilized in VRLA batteries and liquid in flooded-cell batteries, acts as a conduit for ions to move between the positive and negative electrodes of a cell.
• Grid: A lead or lead alloy plate that has been perforated or corrugated and is utilized as a conductor and support for the active substance.
• Anode: The terminal into which current is brought.
• The cathode is the terminal where current leaves the system.
• In VRLA batteries, a valve is utilized to vent gas accumulation that exceeds set thresholds.
• A separator is a tool used to physically separate and electrically isolate electrodes of different polarities.
• Jar: The storage space for the battery’s parts.

Key Takeaway

Battery technology advancements have been more evolutionary than revolutionary. The hazards associated with relying on any battery have been decreased, but not entirely removed, thanks to features like enhanced charging procedures, software management for precise remaining life statistics, and firmware giving intelligence to batteries.

As a result, it is wise, if not necessary, to carefully consider what might be raising your risk of an unplanned load loss due to a failing UPS battery. The failure of a single battery can affect even large installations with numerous batteries.