Complete Guide About AGM Valve Regulated Lead Acid Battery

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2 months ago

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.

What Is an AGM Valve Regulated Lead Acid Battery

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.