Electric energy is the most convenient energy source in our life, and we use it all the time. Today, we have access to electricity anytime, anywhere, and these conveniences are inseparable from rechargeable lithium-ion batteries.
After years of technological innovation, lithium batteries have been continuously improved in comprehensive performance, and have been used in many fields. However, because of this, it is very necessary to conduct comprehensive tests on batteries, because lithium batteries may catch fire and explode when they work abnormally. Accidents, resulting in personal injury and property damage. In various tests of the battery, the battery discharge test is an important part. The discharge test of the battery is of great help to the battery cycle life and discharge performance evaluation.
During the battery discharge test, it is not only necessary to pay attention to the electrical parameters of the battery, but the temperature of the battery is also a very important point, because temperature is one of the factors that directly affects the safety and reliability of lithium-ion batteries. In addition to safety aspects, temperature also has a large impact on the effective capacity and discharge performance of Li-ion batteries. The sharp drop in the performance of electric vehicles in the cold winter is largely related to the performance degradation of the battery in the low temperature environment.
In addition, in actual use, the battery is often charged according to the standards specified by the battery manufacturer. The charging process is relatively smoother and more controllable. However, the discharge process will vary greatly with the load. Once the discharge process A large amount of heat accumulation is generated, exceeding the allowable operating temperature of the battery, which will affect its safety and reliability.
It can be seen that the discharge performance test of the battery under different temperature environments and the temperature change detection during the discharge process are an important step in product development that cannot be ignored. parameter monitoring.
Generally speaking, the performance of the battery is affected by various factors such as battery temperature, battery internal resistance, number of charge and discharge cycles, discharge current, and discharge method. For batteries that have been stored for a period of time, the storage time and storage temperature will also affect to the performance of the battery in use. Therefore, testing the battery discharge characteristics is a long and repetitive task.
The following issues need to be paid attention to in the battery discharge test:
Battery terminal voltage
In the battery discharge test, it is necessary to pay attention to the terminal voltage of the battery at all times. On the one hand, calculating the energy that can be released by the battery needs to be calculated according to the real-time port voltage of the battery to obtain accurate power parameters during the actual discharge process; The battery is damaged or its performance is degraded due to irreversible changes. In order to avoid this situation, the battery test mode of the electronic load needs to set the threshold voltage for termination of discharge. Once the voltage condition for termination of discharge is reached, the electronic load can automatically stop the test without the need for a human. Monitor the battery voltage at all times to avoid over discharge of the battery.
Resistance of wires from battery to electronic load
There must be a certain resistance in the wire between the battery and the electronic load. When the device under test outputs a large current, the voltage drop on the load lead will become non-negligible, which will make the terminal voltage of the electronic load lower than the load current after the establishment of the load current. The actual port voltage of the battery, obviously, this has a direct relationship with the equivalent resistance of the lead wire connecting the cable. In order to ensure that the electronic load can accurately measure the output voltage of the device under test, the electronic load needs to provide an additional remote Sense terminal independent of the plugged terminal. When the electronic load is in the Sense working mode, the Sense function is enabled.
After connecting the Sense terminal and the output terminal of the device under test in the correct way, the electronic load can directly detect the actual voltage of the measured object through the Sense terminal, thereby automatically compensating for the voltage drop caused by the resistance of the electronic load lead, so that the electronic load can accurately measure The terminal voltage of the battery.
During the entire discharge test process, the temperature of the battery is also one of the information that needs to be monitored. On the one hand, during the battery discharge process, the battery will inevitably generate heat due to the ohmic internal resistance, and there will also be heat generated by the internal electrochemical reaction, especially when the battery is discharged at high power, the battery will have a significant temperature rise; On the one hand, the temperature change of the battery will have a significant impact on the performance of the battery. Too high and too low temperature will seriously affect the performance of the battery and even affect the safe use of the battery. In addition, in the later period of the battery life, as the battery performance decreases and the internal resistance increases, the temperature of the battery will rise faster under the same discharge conditions, which may exceed the safety limit of the battery in severe cases, causing a safety risk. For the entire battery pack, limited by the heat dissipation conditions, the heat dissipation capabilities of the battery cells located at different positions of the battery pack will have significant differences. During the discharge process, even if the characteristics of the battery cells are completely the same, the temperature of the battery cells in the battery pack will be unbalanced due to the difference in heat dissipation capacity. Differences or increasing differences in performance between individuals.
To sum up, only by accurately measuring the voltage and temperature of the battery during the discharge process can the discharge characteristics of the battery be more accurately evaluated. Australia E-Nanny Electric factory is a leading battery discharge tester manufacturer and supplier in China. E-NANNY not only produces one product, but the whole line of electrical testing equipment including Hipot tester, transformer test set, gis test set, relay protection test set, cable fault location system, insulation resistance tester and so on. Welcome to know more news about E-NANNY.