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1. Working Principle and Capacity Definition of Forklift Lead-Acid Batteries

(1) Working Principle

The working principle of lead-acid batteries is based on electrochemical reactions. During the charging process, electrical energy is converted into chemical energy and stored in the battery. Under the action of the charging current, lead sulfate on the positive plate gradually transforms into lead dioxide, while lead sulfate on the negative plate is converted into spongy lead. The concentration of sulfuric acid in the electrolyte increases. During discharge, chemical energy is converted into electrical energy. The lead dioxide on the positive plate and the spongy lead on the negative plate react with the sulfuric acid in the electrolyte to form lead sulfate again, while the concentration of sulfuric acid in the electrolyte decreases.

(2) Capacity Definition

The capacity of lead-acid batteries is usually expressed in ampere-hours (Ah), which refers to the amount of electricity that the battery can release under certain discharge conditions. For instance, a 100Ah battery, if discharged at a current of 10A, can theoretically be discharged for 10 hours. In practical applications, battery capacity is affected by various factors, such as the size of the discharge current, discharge time, temperature, and the degree of battery aging. Internationally, to unify the measurement standards of capacity, different discharge rates have been stipulated. Common ones include C20 (20-hour rate capacity), C10 (10-hour rate capacity), C5 (5-hour rate capacity), etc. Take C5 as an example, it refers to the amount of electricity output by the battery when it is discharged at a 5-hour rate current to the specified terminal voltage.

2. Factors Influencing the Capacity Selection of Lead-Acid Batteries in Forklifts

(1) The operation intensity of forklift

Working hours: The daily working hours of a forklift are one of the key factors determining the battery capacity. If forklifts need to work continuously for more than 8 hours a day, such as in large logistics warehouses, ports and other places, where forklifts need to constantly move goods, to avoid frequent charging affecting operation efficiency, large-capacity batteries should be selected.

Load weight: The weight of the goods being transported has a significant impact on the battery capacity demand. When forklifts frequently handle heavy objects weighing more than 3 tons, the motor needs to output greater power and consume more electrical energy. In scenarios such as steel mills and building materials factories where heavy goods are being moved, high-load operations require batteries to have strong discharge capabilities and sufficient power. At this time, large-capacity batteries are a necessary condition for ensuring the normal operation of forklifts. In working environments such as electronics factories and stationery factories where light-load goods are moved, forklifts have relatively lower requirements for battery capacity and can choose batteries with smaller capacity.

Working conditions: Apart from working hours and load weight, the working conditions should not be overlooked either. For instance, if a forklift needs to climb slopes frequently, the motor has to overcome gravity to do work, resulting in a significant increase in power consumption. In environments such as construction sites and mines where there is a large amount of climbing work, large-capacity batteries should be selected to cope with the additional power consumption. In a flat indoor warehouse environment, the operating conditions of forklifts are relatively simple, and the requirement for battery capacity can be appropriately reduced.

(2) Charging Conditions

The distribution of charging facilities: The distribution of charging facilities within an enterprise will affect the selection of battery capacity. If an enterprise has complete charging facilities and multiple charging piles are set up near the forklift operation area, allowing forklifts to be charged for a short time at any time, then it is more appropriate to choose medium-capacity batteries. In this way, the forklift can quickly recharge its battery during breaks and maintain operation throughout the day. Conversely, if an enterprise has only a few centralized charging areas, such as the forklifts being able to be charged centrally only at night, to ensure that the forklifts can work continuously throughout the day without power interruption, it is necessary to choose large-capacity batteries to store sufficient electricity to meet the operation requirements for the entire day.

Charging time limit: The charging time varies for batteries of different capacities. Some large-capacity batteries are equipped with fast charging technology, which can significantly shorten the charging time and improve the utilization rate of the equipment. For instance, some advanced lead-acid batteries for forklifts employ special charging algorithms and materials, which can charge the battery from a relatively low level to around 80% within 1 to 2 hours. If an enterprise uses forklifts at a very high frequency and the charging time is limited, it should give priority to such large-capacity batteries with fast charging functions. For enterprises with relatively ample charging time, batteries with ordinary charging speeds can be chosen. At this point, the selection of battery capacity is more based on other factors such as work intensity.

(3) Types and Specifications of forklifts

The differences among various brands and models: There are numerous forklift brands in the market. Different brands, or even different models of the same brand, have varying requirements for battery specifications. Some high-end models, in pursuit of outstanding performance and stability, have strict matching standards for parameters such as battery voltage, capacity, size and weight. When choosing batteries, it is necessary to refer to the forklift's user manual or technical specification sheet to ensure that the selected lead-acid battery is fully compatible with the forklift model. Otherwise, problems such as inability to install the battery or circuit incompatibility after installation, and decline in forklift performance may occur.

Battery compartment size limit: The size of the forklift battery compartment is a physical factor that restricts the selection of battery capacity. The size of the battery compartment determines the maximum external dimensions that can accommodate batteries. If the selected battery capacity is too large and its size exceeds the battery compartment limit, it will not be able to be installed normally. At the same time, the weight of the battery also needs to be taken into account. An overly heavy battery may affect the balance and handling performance of the forklift, especially for some forklift types that have high requirements for the vehicle's center of gravity and handling performance.

3. Methods and Steps for Selecting the Capacity of Lead-Acid Batteries in Forklifts

(1) Calculate the energy demand of the forklift

Determine the power demand of the forklift: The power demand of the forklift can be estimated by the power of its motor. The rated power of the motor is usually indicated in the product manual of a general forklift.

Estimate energy consumption during operation time: Based on the working hours and power requirements of the forklift, the energy consumption during operation time can be estimated.

(2) Select battery capacity based on energy demand

Consider the depth of discharge of the battery: During the use of lead-acid batteries, the power should not be completely discharged; otherwise, it will seriously affect the battery life. It is generally recommended that the discharge depth of lead-acid batteries be controlled between 50% and 80%.

Adjust capacity in combination with safety factors: To ensure the stable operation of forklifts under various complex working conditions, a certain safety factor also needs to be considered. The safety factor is generally set at 1.1-1.3.

(3) Verify the compatibility of the selected battery capacity

After selecting the battery capacity, it is necessary to compare and verify it with the performance parameters of the forklift. The main checks are whether the voltage, capacity, size and weight of the battery match the design requirements of the forklift. The battery voltage must be consistent with the rated voltage of the forklift motor; otherwise, it will cause the motor to fail to work properly or get damaged. The battery capacity should be able to meet the energy demands of the forklift under various working conditions, while not affecting the overall performance of the forklift due to either excessive or insufficient capacity. The size of the battery should be able to be smoothly installed in the battery compartment of the forklift, and its weight should also be within the designed load-bearing range of the forklift to avoid affecting its stability and controllability.

When verifying the battery capacity compatibility, you can also refer to the actual usage cases and experiences of the same type of forklifts in similar working environments. By consulting other enterprises that use the same or similar forklift models, understand their practical experience in battery capacity selection, and whether there have been problems such as operation interruption due to insufficient battery capacity or resource waste due to excessive capacity.