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At present, there are two types of electric vehicle batteries: lead-acid batteries and lithium batteries! Lead acid batteries have capacities of 12AH, 14AH, 20AH, 24Ah! The capacity of lithium batteries is not necessarily the same because lithium batteries can be combined as you like to obtain large capacity batteries, such as 48V40Ah, 72V80Ah, and so on!

Battery capacity is one of the important performance indicators for measuring battery performance. It represents the amount of electricity released by the battery under certain conditions (discharge rate, temperature, termination voltage, etc.) (JS-150D can be used for discharge testing), which is the capacity of the battery. It is usually measured in ampere hours (abbreviated as A · H, 1A · h=3600C)

The battery capacity is divided into actual capacity, theoretical capacity, and rated capacity according to different conditions. The calculation formula for battery capacity C is C=Δ t0It1dt (integrating current I within t0 to t1 time), and the battery is divided into positive and negative poles

The battery capacity is divided into actual capacity, theoretical capacity, and rated capacity according to different conditions

The minimum capacity required to discharge at 25 ℃ to the termination voltage at a certain discharge rate is the specified capacity of the battery during design and production, which is called the rated capacity of a certain discharge rate RH

Square lithium-ion battery

The battery capacity is generally calculated in AH (ampere hours), and another method is to calculate in watts (W) per cell (W/CELL)

1. Ah (ampere hour) calculation, discharge current (constant current) I x discharge time (hour) T. For example, if the continuous discharge current of a 7AH battery is 0.35A, the time can be continuous for 20 hours

2. The charging time is based on 15 hours, and the charging current is 1/10 of the battery capacity. Fast charging will reduce the battery life

Battery capacity refers to the amount of electricity stored in a battery. The unit of battery capacity is "mAh", and the Chinese name is milliampere hour (for convenience when measuring large capacity batteries such as lead-acid batteries, "Ah" is generally used, and the Chinese name is ampere hour, with 1Ah=1000mAh). If the rated capacity of a battery is 1300mAh, which means that a 130mA current discharges the battery, the battery can continue to operate for 10 hours (1300mAh/130mA=10h); If the discharge current is 1300mA, then the power supply time is only about 1 hour (the actual working time may vary due to individual differences in the actual capacity of the battery). This is an ideal analysis, and the actual working current of a digital device cannot always be constant at a certain value (taking a digital camera as an example, the working current will undergo significant changes due to the opening or closing of components such as the LCD display screen and flash), Therefore, the power supply time that a battery can provide to a certain device can only be an approximate value, and this value can only be estimated through practical operating experience

Usually, we talk about battery capacity in ampere hours, which is based on a specific battery that has already been determined

For example, what is the battery capacity of this mobile phone; The capacity of this electric vehicle battery is determined for different batteries. The battery voltage has been determined, without considering the actual voltage. Simply stating ampere hours can represent the capacity of this battery

However, for batteries with different voltages, we cannot simply use ampere hours to represent capacity. For example, a 12V20AH battery, a 15V20AH battery, even if they are both 20AH, can supply the same power load, and the equipment can work normally, but the duration is different. Therefore, the standard capacity should be measured in power

For example, if a device can support both 12V and 24V, and is powered by a 12V (20AH) battery that can provide one hour of power, then using two pieces in series will result in 24V (20AH). The ampere hour does not increase, but the duration will double. Therefore, the capacity should be considered based on the work that the battery can accommodate, rather than just ampere hours

W (work)=P (power) * T (time)=I (current) * U (voltage) * T (time)

Discussing battery capacity in this way has practical significance and must be truthful, otherwise there may be a claim that a mobile phone battery has a larger capacity than an electric car battery, which is obviously unscientific

Charge a battery with constant current and voltage, and then discharge it with constant current. The amount of electricity released is the capacity of the battery, including batteries, nickel hydrogen batteries, etc. However, lithium batteries are not suitable. They have a minimum discharge voltage of 2.75V, which is usually 3.0V as the lower limit protection voltage. For example, if the capacity of a lithium battery is 1000mAh, the charging and discharging current is 1000mA. Place it at 3.0V within the maximum voltage of 4.2V, The capacity released is the most authentic capacity of a battery

The capacity of a battery is an important indicator to measure its performance. It is generally expressed in ampere hours. The sum of discharge time (hours) and discharge current (amperes) is called capacity=discharge time x discharge current. The actual capacity of a battery depends on the amount and utilization rate of active substances in the battery. The more active substances there are, the higher the utilization rate of active substances, and the larger the battery capacity. Conversely, the smaller the capacity, the higher the utilization rate of active substances in the battery, There are many factors that affect battery capacity, and the common ones are as follows:

(1) The influence of discharge rate on battery capacity

The capacity of lead-acid batteries decreases with the increase of discharge rate, which means that the larger the discharge current, the smaller the calculated capacity of the battery. For example, a 10Ah battery can be discharged for 2 hours with 5A discharge, which is 5 × 2=10; So using 10A discharge can only release 47.4 minutes of electricity, equivalent to 0.79 hours. Its capacity is only 10 x 0.79=7.9 ampere hours. Therefore, for a given battery to discharge at different time rates, there will be different capacities. When talking about capacity, we must know the discharge rate or multiple. Simply put, it is how much current is used to discharge

(2) The influence of temperature on battery capacity

The temperature has a significant impact on the capacity of lead-acid batteries. Generally, as the temperature decreases, the capacity decreases. The relationship between capacity and temperature is as follows:

Ct1=Ct2/1+k (t1-t2). t1t2 is the temperature of the electrolyte, where k is the temperature coefficient of the capacity. Ct1 is the capacity at t1 (Ah), and Ct2 is the capacity at t2 (Ah). In battery production standards, a temperature is generally specified as the rated standard temperature. If t1 is the actual temperature and t2 is the standard temperature (usually 25 degrees Celsius), the negative electrode plate is more sensitive to low temperatures than the positive electrode plate. When the electrolyte temperature decreases, the viscosity of the electrolyte increases, Ions are subject to significant resistance, leading to a decrease in diffusion ability and an increase in electrolyte resistance, resulting in an increase in electrochemical reaction resistance. Some lead sulfate cannot be converted normally, and the charging capacity decreases, resulting in a decrease in battery capacity

(3) The effect of termination voltage on battery capacity

When the battery is discharged to a certain voltage value, a sharp drop in voltage is generated, and in fact, the energy obtained is very small. If it is discharged deeply for a long time, the damage to the battery is considerable. Therefore, it is necessary to terminate the discharge at a certain voltage value, which is called the discharge termination voltage. Setting the discharge termination voltage is of great significance for extending the service life of the battery. Generally, the discharge termination voltage of the electric vehicle battery we repair, the electric motorcycle battery, is 1.75 volts per cell, That is to say, a 12 volt battery has 6 cells, and its discharge termination voltage is 6 x 1.75=10.5 volts [2]

(4) The influence of the geometric dimensions of the electrode plate on the battery capacity

When the amount of active substance is constant, the geometric area of the electrode plate in direct contact with the electrolyte increases, leading to an increase in battery capacity. Therefore, the influence of the geometric size of the electrode plate on battery capacity cannot be ignored

① The influence of plate thickness on capacity

The amount of active substance is constant, and the battery capacity decreases with the increase of electrode thickness. The thicker the electrode, the smaller the contact surface between sulfuric acid and active substance, the lower the utilization rate of active substance, and the smaller the battery capacity

② The influence of electrode height on capacity

In batteries, there is a significant difference in the utilization efficiency of active substances between the upper and lower parts of the electrode plate. Experiments have shown that in the early stages of discharge, the current density in the upper part of the electrode plate is about 2 to 2.5 times higher than that in the lower part. This difference gradually decreases as discharge progresses, but the current density in the upper part is higher than that in the lower part

③ The influence of plate area on capacity

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