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2021-03-25

Introduction of knowledge points of VRLA battery

The English name of VRLA battery is valve regulated lead battery (VRLA battery for short). Its basic feature is that it does not need to add acid and water for maintenance during use. The battery is a sealed structure, which will not leak acid or discharge acid mist. The battery cover is equipped with one-way exhaust valve (also known as safety valve). The function of the safety valve is that when the amount of gas inside the battery exceeds a certain value, that is, when the air pressure inside the battery rises to a certain value, the exhaust valve will automatically open to discharge gas, and then automatically close the valve to prevent air from entering the battery.

Battery capacity refers to the amount of electricity stored in the battery, represented by the symbol C. The commonly used unit is ampere hour, referred to as ampere hour (ah) or milliampere hour (MAH). The capacity of battery can be divided into rated capacity (nominal capacity) and actual capacity. (1) Rated capacity (nominal capacity) the rated capacity refers to the minimum amount of electricity (ah) that the battery should discharge at the current rate of 10 hours at the ambient temperature of 25 ℃.

a. Discharge rate. The discharge current rate and discharge time are divided into two parts. Discharge time rate refers to the time from discharge to the end of discharge voltage under certain discharge conditions. According to IEC standard, the discharge time rate has 20, 10, 5, 3, 1, 0.5 hour rate and minute rate, which are respectively expressed as 20HR, 10hr, 5hr, 3hr, 2hr, 1hr, 0.5hr, etc.

b. Discharge termination voltage. The lowest voltage of lead-acid battery which can be recharged repeatedly at a certain discharge rate at 25 ℃ is called discharge end voltage. Most of the fixed batteries require the termination voltage of 1.8V at 10hr (25 ℃).

c. Rated capacity. The rated capacity of fixed lead-acid battery is regulated to be reached when it is discharged to the end voltage at the current rate of 10 hours at 25 ℃. The rated capacity of 10 hour rate is represented by C10. The current value of 10 hour rate is C10 / 10. (2) Actual capacity actual capacity refers to the amount of electricity that the battery can output under certain conditions. It is equal to the product of discharge current and discharge time, in ah.

Internal resistance of battery

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

Cycle Life

The battery goes through a charge and discharge, which is called a cycle. Under certain discharge conditions, the number of cycles that the battery can withstand before working to a certain capacity is called cycle life. The cycle life of traditional fixed lead-acid battery is about 500 ~ 600 times, that of starting lead-acid battery is about 300 ~ 500 times, and that of valve regulated sealed lead-acid battery is about 1000 ~ 1200 times. One of the factors affecting the cycle life is the performance of the manufacturer's products, and the other is the quality of maintenance work. The floating charge life of VRLA battery is more than 10 years.