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# The influence of lead-acid battery discharge rate on battery capacity

From the reaction formula of the lead-acid battery, it can be seen that in the reaction of 1mol PbO2 and 1mol H2SO4 on the positive electrode, the amount of electricity flowing through the positive electrode is 2F; the reaction of 1mol Pb and 1mol H2SO4 on the negative electrode, the electricity flowing through is also 2F. The positive and negative reactions are written together. 1mol PbO2, 1mol Pb and 2mol H2SO4 react, and the battery emits 2F of electricity. Therefore, it can be said that 1F of electricity in the lead-acid rose battery makes 1mol H2SO4 participate in the reaction and generate the same If 1 mol PbO4 and 1 mol H2O are used, the principle of the charging reaction is the same.

The weight of the battery is much heavier than the theoretical weight. First of all, the active material must have a supporting carrier, which is the grid, which accounts for 25% to 45% of the weight of the plate; connectors, such as busbars, intermediate poles, Conductive parts such as terminal poles also account for part of the weight; the utilization rate of the active material of the positive plate is generally 32% to 55%, the utilization rate of the active material of the negative plate is generally 35% to 68%, and the electrolyte is used except for 37% In addition to ~40% dilute sulfuric acid, the sulfuric acid cannot be fully utilized; the positive and negative electrodes must be separated by a separator, and the entire pole group must be placed in a plastic tank, which all need to occupy weight.

The electricity that can be generated by 1kg of active material derived from the above data is 83.47A·h, which is the theoretical specific capacity value of lead-acid batteries. The actual specific capacity of the battery is 15~23A·h/kg (this value is multiplied by the voltage, which is 30~48W·h/kg).

A battery is a container for storing electrical energy, just like a bucket is a container for storing water. The volume of a water bucket indicates how much water can be stored. A large volume can store more water, but a small volume can store less. Similarly, a large storage battery has more power storage, while a small capacity means less power storage. The unit of battery capacity is expressed in ampere-hour (A·h), which is the product of discharge current (A) and discharge time (h). According to different uses, the capacity of lead-acid batteries ranges from 0.5 to 3000A·h. The discharge capacity of the same lead-acid battery is related to the discharge conditions, such as the discharge rate. The higher the discharge rate, the smaller the discharged capacity. For convenience, constant current discharge (known as constant current discharge) is commonly used for battery measurement, and some are discharged with constant power, but the discharge conditions when the battery is used are various.

The discharge rate refers to the reference amount of the discharge current when the battery is discharged. In order to compare the value of the discharge current easily, use a comparison parameter, such as capacity, discharge time, etc., which is called the discharge rate. For high-current discharge, the discharge current is generally expressed as a multiple of the capacity value, such as 3C20, which means that the discharge current is 3 times the 20h rate capacity value. Assuming that the battery’s 20h rate capacity is 60A·h, and 3 times the 20h rate capacity value 180, the discharge current is 180A. For a discharge with a relatively small current, it is generally expressed in hour rate, such as a 20h rate current. For a bud battery of 60Ad·h (20h rate), the 20h rate current is equal to the capacity divided by the discharge time, that is, 60/ 20=3, that is, when the battery is discharged at 3A, it is called the battery discharge at a rate of 20h.

The discharge rate is expressed by the capacity rate, the greater the rate, the greater the current; the discharge current expressed by the hour rate, the greater the hour rate value, the smaller the discharge current. The various discharge rate capacities of a battery can be obtained by measurement, and there is a certain relationship between them. Because the nature and use of rose batteries are quite different, the relative relationship between different types of battery hour rate capacity is also different. There are also certain differences between manufacturers’ batteries. But the general rule is that the larger the discharge current, the smaller the discharged capacity; the smaller the discharge current, the more discharged capacity.

Starting batteries require high-current discharge performance. Generally, the plate is relatively thin, and the porosity of the plate is relatively high, and the difference between various discharge rates and capacities is relatively small; while the valve-regulated fixed battery has a thick plate. , The porosity of the electrode plate is relatively low, so the difference in discharge capacity between large current discharge and small current discharge is greater.

The relationship between discharge rate and capacity, battery workers have done a lot of research work, put forward a lot of empirical formulas, in 1898 Peukert (Peukert) put forward the empirical formula as
InT=K
In the formula, I-discharge current (A);
T-discharge time (h);
n- constant related to the battery type;
K- a constant related to the amount of active material in the battery.

In order to obtain the n and K values ​​of a given model, the battery is discharged with two currents I1 and I2 to obtain T1 and T2. This empirical formula is within the range of some currents, and the degree of compliance is good. If the range is exceeded, the error may be larger.