Analysis on the internal resistance of the battery and its measurement method

Battery resistance and measurement methods Different types of batteries have different internal resistances. Due to the inconsistency of the internal chemical composition of the battery, the internal resistance of the same type of battery is different. The internal resistance of the battery is very small, we usually use milliohm to mean it. Internal resistance is an important technical indicator to measure battery performance. Under normal conditions, the internal resistance of the battery is small, the discharge current is large, the intensity is increased, and the internal resistance of the battery is large, which reduces the discharge. On the schematic diagram of the discharge circuit, we can separate the battery and the internal resistance into a complete non-internal resistance power supply connected to a very small resistance. Now, suppose an external load is very light, so the voltage distribution on this small resistor is small, and bears a heavy external burden, so the voltage distribution on this small resistor is relatively large, and there will be a part of the internal resistance of power consumption (which may be transformed For heat, perhaps a somewhat chaotic reverse electrochemical reaction). When delivered from the factory, the internal resistance of the rechargeable battery is very small. However, after long-term use, as the internal electrolyte of the battery is dry and the internal chemical activity of the battery decreases, its resistance will gradually increase until the internal resistance of the battery is released to the internal power source, and the battery will die. Most of the aging batteries are due to excessive internal resistance, which constitutes no use value and has to be scrapped. Therefore, we should pay more attention to battery capacity rather than charging capacity. First of all, the problem that the internal resistance is not a fixed value is that when the battery is under different conditions, its internal resistance is not the same; the internal resistance of the battery changes with its service life. From a technical point of view, we generally divide the resistance of the battery into two situations: the internal resistance of the charging state and the discharging state. 1. The internal resistance of the charging state refers to the internal resistance of the battery measured after the battery is fully charged. 2. The internal resistance of the discharged state refers to the internal resistance of the battery measured when the battery is fully discharged (discharged to the specified cut-off voltage). In general, the internal resistance of the charged state is unstable, and the measurement effect is much higher than the normal value. However, the internal resistance of the state of charge is relatively stable, and the measurement of this value has practical significance. Therefore, in the battery measurement process, we use the internal resistance of the state of charge as the measurement standard. Secondly, the general method cannot accurately measure the internal resistance. Maybe we would say that in high school physics class, there is a method to calculate the internal resistance of a battery, using a simple formula + resistance box. However, the accuracy of the resistance box calculation algorithm taught in the physics textbook is too low and can only be used for theoretical teaching. In practice, the application of the root cannot be selected. The internal resistance of the battery is very small, we usually use micro-ohm or milliohm to mean it. In general measurement occasions, we require the measurement accuracy error of the battery internal resistance to be controlled within plus or minus 5%. Such small resistance and such precise requirements require the use of specialized measuring instruments. 3. The battery resistance measurement method is used in current operation. In operation and application, the battery resistance is accurately measured by special equipment. Now let me talk about the battery resistance measurement method used in operation. There are two important methods for measuring battery resistance in current operation: 1. Measurement of DC discharge resistance. According to the physical formula Ru003dU/I, the power of the battery testing equipment passes a large and stable DC current in a short time (generally 2~3 seconds) (currently 40~80 large currents are usually used), and measure the voltage at both ends of the battery. , And calculate the internal resistance of the battery according to the formula. This method has high measurement accuracy. If the control is safe, the measurement accuracy error can be controlled within 0.1%. However, this method has obvious shortcomings: (1) It can only measure large-capacity batteries or batteries, and small-capacity batteries cannot load a large current of 40A~80A within 2 to 3 seconds; (2) When the battery passes a large current, the battery The internal electrodes will have polarization and polarization resistance. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Misunderstanding of mobile phone battery charging 'Eat less and more meals' is more reasonable