What To Know About Sealed Lead Acid Batteries - CleanLink

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Batteries don’t always get the level of attention from end-users that mirrors their importance. They are the powerhouses behind essential equipment, such as large floor care machines, which allow janitors to operate without being tied to a power source for long durations. The continual advancement in battery technology today offers a diverse range of options for users, from sealed to flooded, VRLA, AGM, gel, and TPPL batteries, making it challenging even for well-informed customers to keep track.

Unfortunately, confusion over different battery types often results in inadequate maintenance, ultimately shortening the lifespan of these batteries. Lead acid batteries dominate the cleaning industry, primarily available as flooded or sealed variants. While flooded batteries, known for their affordability and longer cycle life, still power much of today’s floor care equipment, there's growing interest in sealed batteries due to their low maintenance.

“Flooded batteries remain the preferred choice for most floor maintenance equipment,” states Fred Wehmeyer, senior vice president of engineering at U.S. Battery Manufacturing Co., Corona, California. “However, a segment of customers is moving towards sealed lead acid batteries mainly to avoid maintenance hassles.”

Flooded batteries require periodic water addition, while sealed batteries, labeled as “maintenance-free,” eliminate this necessity.

“The electrochemical process in both battery types is similar,” explains Stacy Delzeit, senior applications engineer at Trojan Battery, Santa Fe Springs, California. “Each uses lead and sulfuric acid for electrolytes. The differentiation is that flooded batteries incorporate an antimony additive in the lead, causing the battery to emit gas and hydrogen. Upon gassing, these batteries lose water, necessitating regular refilling. Conversely, valve-regulated batteries don’t contain antimony and, therefore, don’t emit gas or lose water, which eliminates the maintenance requirement.”

Are Sealed Batteries Safer?

Fred Wehmeyer advises his customers that a well-maintained flooded lead acid battery will outlast a sealed one. However, poorly maintained flooded batteries won't last as long as low-maintenance sealed ones.

“It depends on the maintenance program in your facility,” says Wehmeyer. “Additionally, there are scenarios where maintaining a battery could be tough or unattainable, making sealed batteries a favorable technology in such cases.”

Aside from maintenance concerns, safety is another reason why some facilities mandate the use of sealed lead acid batteries.

“All batteries emit some hydrogen gas during charging, which could be explosive in large quantities, depending on the room or container size,” adds Delzeit. “Flooded batteries emit more hydrogen due to venting, as they are open and release gases into the atmosphere. This hydrogen gas buildup is not an issue with valve-regulated batteries, as they are sealed.”

Sealed batteries feature one-way valves to release excess pressure during overcharging and do not spill acid when positioned on their sides, affording flexibility in mounting positions.

“As long as it's not positioned upside down, a VRLA battery should never leak acid,” Wehmeyer confirms. “This is especially advantageous in settings like office environments or food storage where acid spillage must be avoided.”

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Defining VRLA Batteries, AGM Batteries And TPPL Batteries

The sealed lead acid battery (often abbreviated as SLA) presents numerous advantages like compact size, heightened safety, and excellent discharge performance with minimal maintenance. These characteristics have enabled it to supplant traditional acid-proof explosion-proof batteries in several applications.

The design life of a sealed lead acid battery generally exceeds 5 years, with some reaching beyond 20 years. However, their actual service life is commonly between 4 to 8 years, which is significantly less than the theoretical design life.

The Evolution and Advancement of Sealed Lead Acid Batteries

The battery industry has benefited immensely from advancements in metallurgical and chemical technologies, leading to more efficient MF (maintenance-free) batteries. Consequently, SLA batteries became prominent with the integration of gas recombination technology and structural enhancements like the one-way gas valve, which ensures the battery remains sealed.

The improvement of safety valves, which manage gas recombination and prevent leaks, has become critical in ensuring the reliability and safeness of these batteries.

Understanding the Principle, Structure, and Characteristics of Sealed Lead Acid Batteries

Constituents and Operating Principle

A sealed lead acid battery consists of plates, separators, explosion-proof caps, shells, and other components. It utilizes a fully sealed, scarce-liquid structure and the cathode adsorption principle to combine oxygen and hydrogen within the battery, achieving complete sealing.

Based on how sulfuric acid electrolyte is fixed, these batteries are classified into AGM (using ultra-fine glass fiber separators) and GEL (using a silicone gel electrolyte) types. For more information on the differences between agm vs lead acid, kindly click and read it.

Both types employ the cathode absorption principle, where the negative electrode possesses more capacity than the positive electrode. During charging, oxygen is released from the positive electrode and hydrogen from the negative. The early release of oxygen and delayed release of hydrogen prevent water loss from the cells. The reactions involved include: 2Pb+O2=2PbO and 2PbO+2H2SO4=2PbSO4+2H2O.

This reaction minimizes hydrogen evolution at the negative electrode, thereby reducing water loss. The AGM type utilizes pure sulfuric acid as an electrolyte, held in place by the porous separator, which allows the oxygen released to reach and be absorbed by the negative electrode. In GEL batteries, the silicone gel and sulfuric acid mixture forms a gel, which changes shape to create pathways for oxygen transfer from the positive to negative electrodes. Despite differing methods, both ensure a fully sealed effect.

Distinguishing Features

1. Steady electrolyte facilitating oxygen diffusion.
2. Safety valves that allow internal pressure regulation to aid oxygen recombination.
3. Upgraded grid materials using high-purity lead alloys to minimize corrosion.
4. Reinforced shells made of durable, pressure-resistant, explosion-proof materials.
5. No need for water or acid refilling due to their valve-regulated design and internal oxygen cycle mechanism.
6. Space-efficient installation, supporting layered setups.
7. Reduced environmental pollution owing to minimal acid mist and flammable gas escape.
8. Sensitivity to environmental conditions, especially temperature.

Causes Leading to Battery Failure

Sealed lead acid batteries are complex electrochemical systems whose performance and longevity rely on several factors, including material composition, manufacturing processes, and environmental conditions.

For more insights into the Features Of Sealed Lead Acid Batteries, feel free to contact us.

• Positive Plate Corrosion

For batteries used in float charging, corrosion of the positive grid significantly limits battery life. Overcharging produces water and H+, with water reducing acidity and H+ accelerating positive grid corrosion.

• Water Loss

The oxygen recombination mechanism isn't completely efficient, and combined with grid corrosion, leads to water loss. As these batteries are sealed, dehydration cannot be remedied, making it a prime cause of failure.

• Dendrite Formation

Dendrites can form in over-discharged batteries, leading to short circuits and zero voltage failures.

• Negative Plate Sulfation

Lead sulfate formation on the negative plate hampers the battery's charge-discharge abilities, reducing capacity and life.

• Thermal Runaway

Thermal runaway is a result of the closed oxygen cycle mechanism. The sealing prevents proper heat dissipation, leading to potential battery failure due to overheating.

Factors Influencing the Longevity of Sealed Lead Acid Batteries

SLAs are particularly sensitive to environmental factors like temperature, usage patterns, and overcharge conditions.

• Ambient Temperature

High temperatures accelerate plate corrosion and water loss, significantly reducing battery life.

• Overcharging

Excess gas production from overcharging can escape, taking acid mist with it, leading to capacity loss and grid corrosion.

• Excessive Discharge or Low Current Discharge

Over-discharge results in sulfation on the negative plate, increasing internal resistance and reducing lifespan.

Enhancing the Lifespan of Sealed Lead Acid Batteries

• Check Charging and Discharging Cycles

Regular discharge and charge cycles reflect the health status of batteries. It is suggested every 2 years within the first 4 years, then annually. Batteries with less than 90% but more than 80% capacity should be refreshed yearly, while those under 80% should be replaced promptly.

• Internal Resistance Testing

Monitoring the internal resistance helps gauge battery health. Variations in different testing instruments must be accounted for.

• Balanced Charging

While frequent equalization charging is not ideal, guidelines should be followed based on the battery’s current state.

• Addressing Inconsistencies

Even initially consistent batteries can develop inconsistencies over time, necessitating measures to ensure uniform performance.

• Online Monitoring

Given the multiple failure modes of SLAs, monitoring systems can provide timely warnings for issues like high temperature and voltage, charging current anomalies, and short circuits, ensuring prompt corrective action.

Conclusion

Numerous factors affect the lifespan of sealed lead acid batteries, mainly temperature and charging methodologies. Understanding these factors can aid in adopting better maintenance practices, enhancing the operational reliability of such batteries, and preventing premature failure.

For more insights, visit What is an AGM battery?. Consult our experts today!