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Lead-acid Battery

2. The amount of charge a battery can deliver under specific discharge conditions is referred to as the battery's capacity, represented by the symbol C. The commonly used unit is ampere-hours, abbreviated as Ah. The discharge rate is often indicated as a subscript to C, such as: C10, which refers to the discharge capacity over 10 hours; C20, which refers to the discharge capacity over 20 hours.

Battery capacity is divided into rated capacity and actual capacity. The actual capacity refers to the amount of charge a battery can deliver under specific discharge conditions. It is the product of discharge current and discharge time, measured in Ah. Factors affecting the actual capacity during use include discharge rate, cutoff voltage, and temperature. The rated capacity refers to the minimum guaranteed capacity that the battery should deliver under certain discharge conditions.

(1) Deep Discharge
(2) High Current Discharge
(3) High Current Charging
(4) Overcharging
(5) Impact of Surrounding Temperature

Using a low-quality charger, a faulty charger, a charger with excessively high maximum charging voltage parameters, or charging the battery for too long can lead to excessive water loss in the battery, causing the electrolyte to dry out prematurely. This can result in swelling and deformation, ultimately shortening the battery's lifespan.

Valve-Regulated Lead-Acid (VRLA) batteries are classified into two types: AGM (Absorbed Glass Mat) and GEL (Gel-type) batteries.

  • AGM batteries use an absorbed glass fiber mat as the separator, with the electrolyte absorbed between the plates and separator. These batteries have a low electrolyte design, and there is no flowing electrolyte inside. AGM batteries can operate in both upright and horizontal positions.

  • GEL batteries use SiO2 as a gelling agent, with the electrolyte absorbed between the plates and the gel. These batteries typically operate in an upright position.

Depth of Discharge (DoD) refers to the percentage of the rated capacity that is discharged from the battery. For shallow cycle batteries, the DoD should not exceed 25%, while deep cycle batteries can discharge up to 80% of their capacity.

Battery thermal runaway failure occurs when the working environment temperature of a valve-regulated lead-acid battery is too high, or when the charging equipment's voltage is uncontrolled. This causes the battery's charging rate to increase too quickly, leading to a rise in internal temperature. Poor heat dissipation results in overheating, which lowers the internal resistance of the battery. As a result, the charging current increases, further reducing internal resistance. This creates a vicious cycle that continues until thermal runaway causes the battery casing to deform and rupture.

 

To prevent thermal runaway, the following measures should be implemented:

  1. The charging equipment should have temperature compensation or current limiting functions.
  2. Strict control of the safety valve quality to ensure proper venting of gases from the battery.
  3. The battery should be placed in a well-ventilated area, and its temperature should be controlled.

Chargers for valve-regulated lead-acid (VRLA) batteries should have the following features:

  1. Automatic Voltage Regulation
  2. Automatic Current Regulation
  3. Constant Voltage and Current Limiting
  4. Overtemperature Alarm
  5. Ripple Coefficient Not Exceeding 5%
  6. Fault Alarm
  7. Automatic Float/Equalization Mode Switching
  8. Temperature Compensation

When using batteries in series/parallel connections, the following precautions should be taken:

  1. Do not mix different brands, capacities, or old and new batteries together.
  2. When connecting in series, ensure that the batteries are of the same type.
  3. In parallel connections, pay attention to the voltage differences across each circuit.
  4. The cables or connection plates linking the batteries must be of equal length and resistance to ensure balance.

Deep discharge occurs when the battery continues to discharge beyond its cutoff voltage. This can lead to an increase in internal pressure, damaging the reversibility of the positive and negative electrode active materials. After recharging, the battery's capacity may decrease or even result in a short circuit.

Zero voltage occurs when there is a battery circuit break, which can be caused by:

  1. Broken terminal posts
  2. Poor soldering of connections
  3. Poor terminal soldering

The difference between gel batteries and traditional lead-acid batteries goes beyond just the electrolyte being transformed into a gel-like substance. The key features are:

  1. Longer Lifespan: Gel batteries typically have a longer lifespan compared to traditional lead-acid batteries, achieved at a lower industrial cost.
  2. Better Temperature Performance: Gel batteries perform significantly better in both high and low temperature conditions.

The main causes of lead-acid battery failure are:

  1. Reverse Polarity
  2. Short Circuit
  3. Sulfation of the Plates
  4. Plate Bending, Corrosion, and Fracture
  5. Loss of Active Material

A lead-carbon battery is a capacitive type of lead-acid battery where carbon material is added to the negative electrode. In a standard lead-acid battery, the positive electrode's active material is lead dioxide (PbO₂), and the negative electrode's active material is lead (Pb). By mixing carbon material into the negative electrode's active material (Pb), the standard lead-acid battery becomes a lead-carbon battery. This type of battery exhibits double-layer capacitance characteristics, improved low-temperature start-up ability, better charging acceptance, and enhanced performance for high-current charge and discharge, effectively extending the battery's lifespan.