Lithium battery test system
In order to test whether the various protection functions of the battery protection circuit are effective, the main test steps of the battery test system include the following parts.
1) Conventional open-circuit voltage test
The battery function test requires charging the battery for a short time and measuring the open circuit voltage to determine whether the basic charging function of the battery is effective.
2）Overcurrent protection and recovery test
Discharge the cell phone battery at high current with an electronic load and test the internal current cut-off function of its protection circuit. When the discharge circuit is cut off, test whether the battery can resume normal operation.
3）Operating temperature test
Read the resistance value on the temperature sensor through a multimeter to test the working temperature of the battery.
4）Overcharge and recovery test
Over-voltage charging of cell phone battery with power supply to test whether the battery protection circuit can cut off the charging circuit.
5）Over-discharge and recovery test
Over-discharge the cell phone battery with electronic load to test whether the battery protection circuit can cut off the discharge circuit.
(6) AC internal resistance test
Test the battery AC internal resistance by AC internal resistance meter.
Lithium-ion battery testing system
A typical lithium-ion battery test system should include the following test instruments.
● Multi-channel switch for loading different excitations to the parts to be tested and switching different test equipment
● High-precision digital multimeter to complete the DC voltage, current and resistance test of the battery
Two or more multi-channel power supplies for charging the test piece and powering the test fixture
●Electronic load for discharge test of the parts to be tested
AC internal resistance tester for measuring the AC internal resistance of lithium battery at 1kHz AC
IPC and test software to control the device to complete the test
Taking the overcurrent protection and recovery test of lithium battery as an example, we describe the specific testing process.
The computer in the test system issues commands to each instrument in turn through the GPIB interface to control the test process. Firstly, connect the electronic load with the parts to be tested by switching the multiplex switch. Set the electronic load to work in constant current mode, so that the part to be tested outputs a relatively large constant current (e.g. 5A), and after connecting it for 20ms, connect the digital multimeter to the battery output through the multiplex switch as well to test the battery output voltage. If the battery output voltage is 0, it means that the battery protection circuit is activated and the battery output circuit has been cut off, and this item passes the test. If the test result is not zero, this goal is set as a test failure. After the test, quickly open the switch and cut off the connection between the electronic load and the battery, because the long time high current discharge may cause permanent damage to the battery.
Based on the above test solutions, Agilent introduced a new generation of lithium-ion battery test solutions in 2007. The new solution makes extensive use of the LXI (LANExtensionsforInstrumentation) system test instruments introduced in recent years. Compared with traditional products, these LXI instruments simplify the difficulty of system integration by setting up the system through a network cable, increase the test speed, and significantly reduce the system size and set-up cost. In some cell phone battery manufacturers' applications, customers tell us that the new solution reduces the size of the system by more than 1/3 and the cost by more than 1/4 compared to their original test system configuration, while the test speed is also There is an increase of about 10% in test speed. The smaller chassis size, simpler system connections and lower power consumption from the switching power supply also bring many additional benefits.
In terms of test software development, LXI instruments also support a variety of mainstream software development environments and can write test programs in VB, VC, C/C++, Labview, and other development environments, in exactly the same way as traditional instrument control.
In the process of battery testing, the most important concerns of customers include not only ensuring the quality of batteries, but also how to improve battery yield and reduce production costs. In addition, due to the different electrical characteristics of different battery models, the test system must have a certain degree of flexibility in terms of software and hardware to facilitate secondary development on the system by the customer. Finally, in the face of the production line 24 hours a day continuously on the conditions, the quality of the system instrumentation, maintenance costs, is also an important factor to measure the battery test system solutions.
Selection of multiplexer switches in battery test systems.
In single-cell battery testing, multiplex switches are mainly used to connect different loads or power sources to the battery for repeated charge/discharge testing, and they can also be used to switch the measurement instrumentation. In the common battery testing process, it takes about dozens of switch switching steps to complete all tests on a single cell, and the production line usually produces more than 8,000 cells per day, and the maximum number of times a single switch is opened and closed in a day can reach more than 150,000 times. Therefore, good switch quality and fast switching rate are the key to choosing a switch product.
A wide range of high quality switch inserts are available in the Agilent 34980A. These switches provide the fastest opening and closing time and the longest switch life in the same category, and the switch count function can report the working status of each switch in time, so that the switch that is about to fail can be replaced in advance. In addition, its built-in digital multimeter can directly complete the high-precision measurement of various DC signals. It can save investment and improve system integration and testing speed.
Selection of multiple power supplies in battery test systems
In the battery test, the power supply loaded on the part to be tested will be more than two ways, excluding the power supply for the fixture of the part to be tested, these power supplies are also used to charge the battery and simulate various overvoltage and overcharge phenomena, and detect the response of the battery protection circuit. When conducting such tests, the response speed of the power supply is very critical, usually overcharge the battery, the time can not exceed 1 second, otherwise it may cause the battery to burn and explode, and to ensure the speed of the test, this time is generally limited to a few hundred milliseconds.
N6700 modular DC power supply, each power supply chassis in the 1U height can be placed in up to four power modules, forming a mutually independent multiple power supply. In addition, these power supply modules have built-in voltage and current measurement capabilities, allowing monitoring of output status without switching to other measurement instruments. In automatic test systems, modular power supply systems can significantly reduce the size of multiple power supplies, reduce system costs, and become the preferred power supply for building test systems today.
Selection of electronic load in battery test system
The electronic load is used to test the discharge of the battery and to simulate whether the internal protection circuit can cut off the battery output in time when the battery is short-circuited with high current output. In the battery test, the high current discharge time cannot exceed 30ms, otherwise it will cause accidental battery combustion or explosion, so in order to ensure the test safety, the response speed and current change speed of such test is very high.
Agilent provides a variety of electronic load products, including fast current change speed, up to 107A / S. Built-in 16bit voltage and current readback function, you can measure the voltage and current value in real time under the working state, without switching to other devices.
Selection of AC internal resistance tester
The internal resistance value of the battery is directly related to the quality of the battery cell and the quality of the battery package. If the measured internal resistance value of the battery is higher than the expected value, it will indicate that the battery quality is likely to be problematic. Since lithium-ion batteries are often accompanied by dynamic loads and often generate a large number of current pulses during operation, measuring battery AC internal resistance at 1 kHz has become the industry standard for battery internal resistance measurement. The lower the internal resistance of the battery, the more stable the voltage value of the battery output. Therefore, measuring the internal resistance of a battery at 1 kHz will give a very strong indication of the battery's ability to regulate its own output voltage under dynamic negative carrier conditions. Agilent Dynamic Internal Resistance Tester 4338B can help solve the problems on AC internal resistance testing and provide high speed and accurate measurement results.
With these instruments above, an efficient battery testing system can be set up very quickly. Most of these instruments have good expansion capabilities, such as the 34980A switching system, which can be extended with more measurement channels by inserting a card, and the N6700, which can increase the number of power supplies in the system or increase the power output power by inserting a power supply module, etc. This system also has a good expansion function, after very simple modification, can be applied to other large-capacity battery testing, such as PDA, notebook computers and digital video cameras, etc. battery testing.
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