About battery internal resistance and measurement method

　　Author ：Iflowpower – Portable Power Station Supplier

Different types of battery internal resistance. The same type of battery, due to the inconsistency of internal chemical characteristics, internal resistance is different. The internal resistance of the battery is small, we generally use millis units to define it.

Internal resistance is an important technical indicator for measuring battery performance. Under normal circumstances, the large current discharge capacity of the internal resistance is strong, and the internal battery discharge capacity is weak. On the schematic of the discharge circuit, we can consider the battery and internal blocking, divided into a power string that completely no internal resistance to connect a very small resistance.

At this time, if the external load is light, the voltage assigned on this small resistor is small, and vice versa if the external load is loaded, then the voltage allocated on this small resistor is relatively large, there will be part of the power being consumed in this Introelectric (possibly converted to fever, or some complex reverse electrochemical reactions). An internal resistance of a rechargeable battery is relatively small, but after long-term use, due to the depletion of the internal electrolyte of the battery, the internal block is gradually increased, until the internal resistance is large to the battery. The internal power cannot be released normally.

At this time, the battery is "life is dead". Most of the aging batteries are due to the excessive reasons of the internal resistance, there is no use value. Therefore, we should pay more attention to the capacity of the battery is not inheonded.

First, the internal resistance is not a fixed value, when the battery is in different power states, its internal resistance value is different; the battery is in different service life, its internal resistance value is also different. From the perspective of technology, we generally score the electric resistance of the battery to two states: charging state internal resistance and discharge state internal resistance. 1.

The inside of the charging state means the measured battery in the battery is fully charged. 2. Put the internal resistance of the battery to refer to the battery internal resistance measured after the battery is fully discharged (discharging to standard cutoff voltage).

In general, the internal resistance of the discharge is unstable. The results of the measurement are much higher than the normal value, and the recharge state is relatively stable, and the measurement is actually more significant. Therefore, in the measurement of the battery, we all made the measurement of the measurement in the charge state.

Second, the internal resistance cannot be used to accurately measure the general method may say that the high school physics class has a simple formula + resistance box to calculate the internal resistance of the internal resistance . but the physical class is based on the resistance of the resistance box to calculate the algorithm accuracy of the resistance box Too low, only the teaching of theory can only be used in practical applications. The internal resistance of the battery is small, we generally define it with micro Europe or milliocanel units.

In general measurement, we require the internal resistance measurement accuracy error of the battery to be controlled within 5%. Such a small resistance and such accurate requirements must be measured with a dedicated instrument. III.

In the current industry, the battery internal resistance measurement method industry is applied, the accurate measurement of the internal resistance is conducted by special equipment. Let me talk about the battery internal resistance measurement method used in the industry. The battery internal resistance measurement method applied in the current industry has the following two types: 1.

DC discharge internal resistance measurement. According to the physical formula R = U / I, the test device allows the battery to force the battery through a large constant DC current (currently using a large current of 40A to 80A) in a short period of time (currently using 40A to 80A), measure the battery The voltage at both ends and calculates the current battery internal resistance according to the formula. The accuracy of this measurement method is high and controlled.

The measurement accuracy error can be controlled within 0.1%. However, this method has a significant shortcomings: (1) can only measure a large-capacity battery or battery, a small capacity battery that does not load 40A to 80A in 2 to 3 seconds; (2) When the battery is passed through a large current The electrodes inside the battery will cause polarization, generating polarized internal resistance.

Therefore, the measurement time must be short, otherwise the measured internal resistance error is large; (3) large current is damaged by the electrode inside the battery through the battery. 2. AC pressure drop internal resistance measurement.

Because the battery is actually equivalent to an active resistance, we apply a fixed frequency and fixed current to the battery (currently using 1 kHz frequency, 50mA small current), then sample the voltage, rectification, filtering, etc. The internal resistance value of the battery is calculated by the op amp circuit. The battery measurement time of the AC pressure dropped internal resistance method is extremely short, generally in 100 milliseconds.

This accuracy of this measurement method is also good, and the measurement accuracy error is generally between 1% to 2%. The advantages and disadvantages of this method: (1) Almost all batteries can be measured using an alternating internal resistance measurement method, including small capacity batteries. The internal resistance measurement of the laptop battery cell is generally in this way.

(2) The measurement accuracy of the AC pressure drop measurement method is likely to be affected by the ripple current, and there is also possible possible to interfere with harmonic current. This is a test for the anti-interference ability in the measuring instrument circuit. (3) Measurement with this method, there will be no too much damage to the battery itself.

(4) The measurement accuracy of the AC pressure drop measurement method is not as good as DC discharge internal resistance measurement. 3. Test the component error of the instrument and the battery connection line problem for testing.

Whether it is the above method, there are some problems that are easily ignored by us, that is, the component error of the test instrument and the test cable problem for connecting the battery. Because the internal resistance of the battery to be measured is small, the electrical resistance of the line will take into account. A short slave from the instrument to the battery itself also has a resistor (approximately Micro-European grade), as well as the contact resistance of the battery and the connection line, these factors must be in the instrument's internal prior error adjustment.

Therefore, the formal battery internal resistance test is generally equipped with a dedicated cable and battery fixing shelf. Fourth, summarizing a lot of aging batteries, the internal power is still a lot, but the internal resistance is too large, it is unfortunately. However, once the internal resistance of the battery is increased, it is difficult to reduce this internal resistance value.

Therefore, for the aging battery, even if we want to "activate" it, such as large current shocks, small current floating, put a refrigerator, but most of them, return to the heavens. After understanding the above knowledge, we basically know that selecting a battery to select a small-resistant battery as much as possible. In addition, it is important, the battery is not used, and its internal resistance will continue to increase.

It is recommended that you still need to use the battery to keep the activity of the internal chemical substance of the battery.