Technical performance parameters of lead-acid batteries
The technical performance parameters of lead-acid batteries are mainly composed of static electromotive force, internal resistance and capacity.
(1) Static electromotive force
Exquisite electromotive force means that the lead-acid battery is in a static state (no charging or discharging), and the potential difference between the positive and negative electrodes of the single cell depends on the relative density and temperature of the electrolyte. The general static electromotive force Ej can be expressed by the following empirical formula:
Where Ej is the resting electromotive force (V); γ 25 ° C is the relative density of the electrolyte at 25 ° C.
The relative density of the measured electrolyte should be converted to the relative density of the electrolyte at 25 ° C. The conversion relationship is
Γ25°C=γt+β(t-25) where γt is the measured relative density of the electrolyte; t is the measured electrolyte temperature (°C); β is the relative density temperature coefficient, and the value is 0.00075.
(2) Internal resistance
The size of the internal resistance of the lead-acid battery reflects the capacity of the battery load. Under the same conditions, the smaller the internal resistance, the larger the output current and the stronger the load carrying capacity. The internal resistance of lead-acid batteries includes the resistance of plates, separators, electrolytes, joints and poles. The plate resistance is very small in the fully charged state, but as the battery discharge degree increases, the PbSO4 covering the surface of the plate increases, and the plate resistance increases accordingly. The separator resistance mainly depends on the separator. Material, thickness and porosity. Among the commonly used separators, the microporous plastic separator has a small electrical resistance. The electrical resistance of the electrolyte is related to the temperature and relative density of the electrolyte. When the temperature is lowered, the viscosity of the electrolyte increases, the permeability decreases, and the resistance increases. When the relative density of the electrolyte is too high and too low, the resistance increases.
The capacity of the lead-acid battery marks the ability of the battery to supply power externally and is the main performance parameter of the battery. The fully charged battery, the amount of electricity output in the allowed discharge direction is called the capacity of the battery, which can be expressed by:
Where C is the capacity of the battery (A·h); If is the discharge current (A); tf is the discharge time (h).
According to the national standard GB5008。1-1991 "Technical conditions for the start-up lead-acid battery", the new battery with sufficient electricity will have a discharge rate of 20h at a temperature of (25±5) °C。 0。05C20A) Continuous discharge until the voltage of the single cell drops to 1。75V, the output of the battery is called the rated capacity of the battery, which is expressed by C20。 For example, the “100” of the 6-CA-100 lead-acid battery is the rated capacity。 , that is, the rated capacity, that is, the design capacity, is one of the important signs for checking the performance of the battery。
2。 Startup capacity
The starting capacity characterizes the power supply capability of the lead-acid battery when the engine is started, and is one of the important indicators for checking the quality of the battery. The starting capacity is greatly affected by the temperature, so it is divided into two types: normal temperature starting capacity and low temperature starting capacity.
(1) Normal temperature starting capacity
The normal temperature starting capacity refers to the amount of electricity output from a new battery that is fully charged, at a temperature of 25 ° C, with a current of 3 C20 A for more than 5 min, until the cell voltage drops to 1.5 V. For example: 6- The CA-100 lead-acid battery is continuously discharged for 5 minutes at a large current of (3 × 100) A = 300 A, and the room temperature starting capacity is (300 × 5 / 60) A · h = 25 A when the cell voltage drops to 1.5 V. · h, generally 1/4 of the rated capacity.
(2) Low temperature starting capacity
The low-temperature starting capacity refers to a new battery that is fully charged. When the electrolyte temperature is 18 ° C, the current is continuously discharged for 3 min at a current of 3 C 20 A until the cell voltage drops to 1 V. For example: 6-CA The -100 type lead-acid battery is continuously discharged for 2.5 min at a large current of (3 × 100) A = 300 A until the cell voltage drops to 1 V, and its low-temperature starting capacity is (300 × 2.5 / 60) A · h = 12.5 A · h, generally 1/8 of the rated capacity.