What are the parameters of the car battery

1. Battery electromotive force, open circuit voltage and working voltage

When the battery conductor is connected externally, the electrochemical reaction between the positive electrode and the negative electrode will occur spontaneously. If the conversion of electric energy and chemical energy in the battery reaches a balance, the difference between the balance electrode potential of the positive electrode and the balance electrode potential of the negative electrode is the battery electromotive force, which is numerically equal to the open circuit voltage when reaching a stable value. The product of electromotive force and unit electric quantity, representing the maximum electric work that can be done per unit electric quantity. However, the significance of electrodynamic heat of battery is different from that of open circuit voltage: the electromotive force can be calculated by thermodynamics or by measurement according to the reaction in the battery, which has clear physical significance. The latter is only numerically close to the emf, depending on the degree of reversibility of the battery.

The terminal voltage of the battery in the open circuit state is called the open circuit voltage. The open circuit voltage of the battery is equal to the difference between the positive electrode potential and the negative electrode potential of the battery.

The working voltage of a battery is the voltage at which the battery has a current passing through (closed circuit). The operating voltage at the beginning of the battery discharge is called the initial voltage. After the battery is connected to the load, the working voltage of the battery is lower than the open circuit voltage due to ohmic resistance and polarization overpotential.

2, capacity,

Battery capacity refers to the amount of battery energy stored, represented by the symbol C. Common units are the ampere hour, referred to as the ampere-hour (Ah) or the milliampere-hour (mAh).

Battery capacity can be divided into rated capacity (nominal capacity), the actual capacity.

(1) rated capacity

The rated capacity of the battery is at 25 ℃ ambient temperature, the rate of discharge current 10 hours, should let out the minimum power (Ah).

A. discharge rate. Discharge rate is for the battery discharge current size, divided into time rate and current rate.

Discharge time rate refers to the length of time from discharge to discharge terminal voltage under certain discharge conditions. According to IEC standard, the discharge time rate is 20,10,5,3,1,0.5 hour rate and minute rate, respectively expressed as 20Hr, 10Hr, 5Hr, 3Hr, 2Hr, 1Hr, 0.5Hr, etc..

B. discharge termination voltage. Lead battery at a certain discharge rate at 25 ℃ ambient temperature to devolve electricity to the minimum voltage to recharged again use referred to as the end of the discharge voltage. Most of the fixed type battery regulation with 10 hr discharge (25 ℃) termination voltage of 1.8 V/only. The termination voltage depends on the discharge rate and the need. In general, for the safe operation of the battery, the value of the termination voltage is slightly higher for a small current discharge less than 10Hr and slightly lower for a large current discharge more than 10Hr. In the communication power system, the terminal voltage of the battery discharge is determined by the basic voltage requirement of the communication equipment.

Discharge current rate is to compare the nominal capacity of different battery discharge current size and set, usually with 10 hours rate current as of the standard, with I10, 3 hours rate and 1-hour rate discharge current respectively with I3, I1.

C. rated capacity. Fixed lead-acid battery regulation under 25 ℃ environment, 10 hours rate discharge current to voltage can reach the end of the rated capacity. The 10 - hour rate rated capacity is expressed in C10. The current value of the 10-hour rate is

Capacity under other hourly rates can be expressed as:

3 hours rate capacity (Ah) expressed in C3, at 25 ℃ ambient temperature measured capacity (Ah) is the product of the discharge current and discharge time (h), fixed type valve-controlled lead-acid battery C3 and I3 value should be

C3 = 0.75 C10 (Ah)

I3 = 2.5 I10 (h)

1 hour fixed capacity (Ah) is represented by C1, and the measured values of C1 and I1 should be

C1 = 0.55 C10 (Ah)

I1 = 5.5 I10 (h)

(2) actual capacity

The actual capacity refers to the amount of electricity the battery can output under certain conditions. It's the product of the discharge current times the discharge time, in Ah.

3, internal resistance

Battery internal resistance includes ohmic resistance and polarization resistance, polarization resistance includes electrochemical polarization and concentration polarization. The existence of internal resistance makes the terminal voltage lower than the electromotive force and open circuit voltage when the battery is discharged, and higher than the voltage of electromotive force and open circuit when the battery is charged. The internal resistance of the battery is not constant and changes with time in the process of charging and discharging because the composition of the active material, electrolyte concentration, and temperature are constantly changing.

Ohm resistance obeys Ohm's law; The polarization resistance increases with the increase of current density, but it is not linear.

4. Cycle life

The battery undergoes a charge and discharge, called a cycle (one cycle). Under certain discharge conditions, the number of cycles the battery can withstand before the battery works to a certain capacity regulation value is called cycle life.

The cycle times of all kinds of batteries are different. The traditional fixed lead-acid battery is about 500~600 times, and the starting lead-acid battery is about 300~500 times. The cycle life of a valve-controlled sealed lead-acid battery is 1000~1200 times. Factors affecting cycle life are the performance of the manufacturer's products and the quality of the maintenance work. The life of the fixed lead battery can also be measured by floating charge life (years). The floating charge life of the valve-controlled sealed lead acid battery is more than 10 years.

For the starting lead-acid battery, according to the standards of China's ministry of mechanical and electrical, the number of overcharge endurance and cycle endurance units is used to express the life, but the number of cycles is not used to express the life. That is, the number of overcharge units should be more than 4, and the number of cyclic endurance units should be more than 3.

5, energy

The energy of a battery is the amount of energy, usually in watt-hours (Wh), that can be produced by the battery under a certain discharge regime.

The battery energy is divided into theoretical energy and practical energy. The theoretical energy W can be expressed as the product of the theoretical capacity and the electromotive force (E), i.e

W =C E

The actual energy of the battery is the product of the actual capacity C under certain discharge conditions and the average working voltage U, i.e

W real equals C real U squared

Specific energy is often used to compare different battery systems. Specific energy refers to the electric energy that can be output per unit mass or volume of the battery, which is Wh/kg or Wh/L respectively.

Specific energy is divided into theoretical specific energy and practical specific energy. The former refers to the theoretical output of 1kg of battery reactive material when fully discharged. The actual specific energy is the actual energy that can be output by the reaction material of 1kg battery.

Due to various factors, the actual specific energy of the battery is far less than the theoretical specific energy. The relation between actual specific energy and theoretical specific energy can be expressed as follows:

W real =W truth? KV? KR? Km

Where, KV - voltage efficiency; KR -- reaction efficiency; Km -- mass efficiency.

Voltage efficiency is the ratio of the working voltage of a battery to its electromotive force. When the battery is discharged, the operating voltage is less than the electromotive force due to electrochemical polarization, concentration polarization, and ohmic voltage drop.

The reaction efficiency represents the utilization rate of the active substance.

The specific energy of the battery is a comprehensive index, which reflects the quality level of the battery and indicates the technology and management level of the manufacturer.

6. Storage performance

During storage, there are impurities in the battery, such as positive electric metal ions. These impurities can be combined with negative active substances to form a microbattery, which will lead to the dissolution of negative metal and the precipitation of hydrogen. If the standard electrode potential of the impurities dissolved in the solution and from the positive electrode grid is between the positive electrode potential and the negative electrode potential, it will be oxidized by the positive electrode and reduced by the negative electrode. So the existence of harmful impurities, so that the positive and negative electrode active material is gradually consumed, and cause the loss of capacity of the battery, this phenomenon is called self-discharge.

The battery self-discharge rate is expressed by the percentage of capacity reduction per unit time: that is, the percentage of capacity difference before battery storage (C10 ') (C10 ") and storage time T (days and months).

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