The agm valve regulated lead acid battery is widely used in backup power. It is also used in renewable energy storage and telecommunication systems. This is because of its sealed, maintenance-free design. Unlike traditional flooded lead-acid batteries, AGM batteries use fiberglass mats to absorb the electrolyte, preventing leaks and reducing maintenance requirements. Their valve-regulated design allows safe operation without the need for frequent water refilling. This makes them ideal for standby applications. They are also suitable for cyclic applications.
How AGM Valve Regulated Lead Acid Battery Work
AGM batteries feature a microporous glass fiber separator that holds the electrolyte in place between the positive and negative plates. This design enhances efficiency by reducing internal resistance and enabling higher discharge rates. The valve-regulated system maintains internal pressure and safely vents excess gases, ensuring safety and long service life.
Sealed Valve-Regulated Design
Unlike conventional flooded lead acid batteries, AGM VRLA batteries are sealed and equipped with a pressure relief valve. This design allows gases generated during charging to recombine internally, minimizing electrolyte loss and eliminating the need for water refilling. The valve-regulated system only vents excess gas when internal pressure exceeds safe levels, ensuring both safety and long service life.
Absorbent Glass Mat Technology
At the core of AGM batteries is the glass fiber separator:
- Electrolyte Absorption: The porous glass mat absorbs and immobilizes the sulfuric acid electrolyte, preventing leaks and enabling a spill-proof design.
- Capillary Action: The fibers hold electrolyte in close contact with the active material, improving ion transport and enhancing charge/discharge efficiency.
- Starved Electrolyte System: A controlled amount of electrolyte is used, which helps oxygen recombination and reduces gas buildup.
Internal Structure and Design
An AGM valve regulated lead acid battery consists of several carefully engineered components:
- Positive and Negative Plates: Made from lead dioxide (positive) and sponge lead (negative) to store and release energy.
- Glass Mat Separator: Holds the electrolyte and enhances conductivity.
- Electrolyte: Diluted sulfuric acid immobilized within the glass mat.
- Battery Case: Sealed ABS or polypropylene housing to give structural strength and resistance to shock and vibration.
- Safety Valves: Prevent overpressure while ensuring sealed operation.
Charging Characteristics
AGM valve regulated lead acid battery can need a constant voltage, limited current charging method. The charging process typically includes three stages:
Bulk Charge – The battery is charged at a constant current until the voltage reaches the absorption level.
Absorption Charge – The voltage is held constant while the current gradually decreases as the battery nears full capacity.
Float Charge – A lower voltage is applied to keep full charge and compensate for self-discharge, preventing overcharging.
- Recommended Voltage: Typically 2.25 – 2.30V per cell for float charging and 2.40 – 2.45V per cell for cycle charging.
- Temperature Compensation: For every 1°C change from 25°C, adjust the charging voltage by about –3mV per cell. This adjustment helps avoid thermal runaway.
- Overcharging Risk: Excessive voltage can dry out the electrolyte, increase internal resistance, and reduce service life.
Discharging Characteristics
When supplying power, AGM valve regulated lead acid battery can deliver stable voltage and strong discharge ability.
Discharge Curve
AGM batteries offer a relatively flat voltage curve during discharge, maintaining consistent power until nearing depletion.
Depth of Discharge (DoD)
The deeper the discharge, the shorter the cycle life. For example, 50% DoD yields more cycles than 80% DoD.
High Rate Discharge
Thanks to low internal resistance, AGM valve regulated lead acid battery can deliver high current quickly. This ability is useful for UPS and engine start applications.
Cut-off Voltage
Discharging below the manufacturer’s recommended cut-off (typically 1.75 – 1.8V per cell) may cause permanent damage.
Internal Resistance
Internal resistance is a critical parameter that influences battery performance. It opposes the flow of current within the battery. It is composed of the resistance of electrodes, electrolyte, and separators.
Impact
- Higher resistance leads to voltage drop under load.
- Causes heat generation during high-current charging/discharging.
- Reduces efficiency and shortens service life.
Factors Affecting Internal Resistance
- Battery age: Resistance increases as the battery ages.
- State of charge: Lower charge levels often result in higher resistance.
- Temperature: Cold temperatures raise resistance, reducing performance.
Typical Range
A new AGM battery usually has an internal resistance between 3–10 milliohms depending on size and capacity.
Related AGM Valve Regulated Lead Acid Battery
Applications
AGM VRLA batteries are widely used across industries due to their reliability and versatility. Common applications include:
- Uninterruptible Power Supply (UPS) systems
- Telecommunication equipment and base stations
- Renewable energy storage (solar and wind systems)
- Emergency lighting and security systems
- Electric vehicles and mobility scooters
- Marine and RV power systems
- Medical equipment backup
Advantages
Compared to flooded lead-acid batteries, AGM valve regulated lead acid battery can offer several benefits:
- No acid spills due to sealed construction.
- Lower maintenance costs since they need no regular servicing.
- Longer service life in standby and cyclic use.
- Enhanced safety with controlled gas recombination.
- Compact and lightweight design, offering better energy density.
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