At present, the common methods for measuring the internal resistance of batteries are:
(1) Density method
The density method mainly estimates the internal resistance of the battery by measuring the density of the battery electrolyte. It is often used for the internal resistance measurement of open-ended lead-acid batteries, and is not suitable for the internal resistance measurement of sealed lead-acid batteries. The scope of application of this method is narrow.
(2) Open circuit voltage method
The open circuit voltage method estimates the internal resistance of the battery by measuring the terminal voltage of the battery. The accuracy is very poor, and even wrong conclusions can be drawn. Because even a storage battery whose capacity has become very small, its terminal voltage may still behave normally under the re-floating state.
(3) DC discharge method
The direct current discharge method is to measure the instantaneous voltage drop on the battery by discharging the battery with an instantaneous high current, and calculate the internal resistance of the battery by Ohm's law. Although this method has been widely used in practice, it also has some shortcomings. If this method is used to detect the internal resistance of the battery, it must be done in a static or offline state, and online measurement cannot be achieved. Moreover, high-current discharge will cause greater damage to the battery, thereby affecting the capacity and life of the battery.
(4) AC injection method
The AC method injects a constant AC current signal IS into the battery to measure the voltage response signal Vo at both ends of the battery, and the phase difference θ between the two is used to determine the internal resistance R of the battery by the impedance formula. This method does not need to discharge the battery, and can realize the online detection of the internal resistance of the battery, so it will not affect the performance of the battery. However, this method needs to measure the AC current signal Is, the voltage response signal Vo, and the phase difference θ between the voltage and the current. It can be seen that this method not only has many interference factors, but also increases the complexity of the system and also affects the measurement accuracy. .
(5) Internal resistance tester
The battery internal resistance tester adopts an advanced AC discharge test method, which can accurately measure the voltage and internal resistance at both ends of the battery, and use this to judge the battery capacity and technical status of the battery. Customers can choose the internal resistance test, voltage test, and capacity estimation of the battery according to their own conditions. As the basis for matching the internal resistance of the new battery pack; test the internal resistance of the battery before and after discharge to identify the true backward battery; two operation modes: key operation and LCD touch; it can be used for group measurement of batteries or single Section measurement.