Building an efficient lithium-ion battery test system based on LXI bus

Mobile phone lithium battery testing mainly tests the function of the battery protection circuit after packaging, using power supplies, electronic loads, multi-way switches, digital multimeters and other instruments to simulate various extreme overvoltage and overcurrent conditions during charging and discharging to detect whether the battery protection circuit is effective. This prevents substandard battery products from entering the market from the source.

Lithium-ion battery testing requirements

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
Battery function test requires short-term charging of the battery and measuring the open circuit voltage to determine whether the basic charging function of the battery is effective.
2) Overcurrent protection and recovery test
Use an electronic load to discharge the mobile phone battery with a large current and test the internal current cut-off function of its protection circuit. After cutting off the discharge circuit, test whether the battery can resume normal operation.
3) Working temperature test
Read the resistance value on the temperature sensor through a multimeter to test the battery working temperature.
4) Overcharge and recovery test
Use a power supply to over-voltage charge the mobile phone battery to test whether the battery protection circuit can cut off the charging circuit.
5) Overdischarge and recovery test
Use an electronic load to over-discharge the mobile phone battery to test whether the battery protection circuit can cut off the discharge circuit.
6) AC internal resistance test
Test the battery AC internal resistance through an AC internal resistance meter.

Lithium-ion battery testing system

A typical lithium-ion battery testing system should include the following testing instruments:

● Multi-channel switch is used to load different excitations to the DUT and switch different test equipment.
● High-precision digital multimeter is used to complete the 直流电\'); companyAdEvent.show(this,\'companyAdDiv\',[5,18])"> DC voltage, current and resistance test of the battery.
● Two or more multi-channel power supplies are used to charge the DUT and power the test fixture.
● Electronic load is used to discharge the DUT.
● AC internal resistance tester is used to measure the AC internal resistance of lithium batteries under 1kHz AC.
● Industrial computer and test software are used to control the equipment to complete the test.

Taking the overcurrent protection and recovery test in lithium battery testing as an example, let's describe the specific test process: The computer
in the test system sends instructions to each instrument in turn through the GPIB interface to control the test process. First, connect the electronic load to the DUT by switching the multiplexing switch. Set the electronic load to work in constant current mode so that the DUT outputs a relatively large constant current (for example, 5A). After 20ms, connect the digital multimeter to the battery output terminal through the multiplexing switch 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 project has passed the test. If the test result is not zero, this project is considered a test failure. After the test, quickly turn on the switch to cut off the connection between the electronic load and the battery, because long-term high-current discharge may cause permanent damage to the battery. Based on the above test plan, Agilent launched a new generation of lithium-ion battery testing solutions in 2007. The new solution uses a large number of LXI (LAN Extensions for Instrumentation) system test instruments launched in recent years. Compared with traditional products, these LXI instruments use network cables to build systems, simplify the difficulty of system integration, improve test speed, and greatly reduce system volume and assembly costs. Each instrument in the system is connected to the computer through a network cable or GPIB cable to form a hybrid test system based on the LXI platform. The height of the entire system is only 14U. In the actual application of some mobile phone battery manufacturers, customers told us that compared with their original test system configuration, the new solution has reduced the system volume by more than 1/3, reduced the cost by more than 1/4, and increased the test speed by about 10%. In addition, the smaller chassis size, simpler system connection and the lower power consumption brought by the switching power supply also bring many additional benefits. In the development of test software, LXI instruments also support various mainstream software development environments. Test programs can be written in various development environments such as VB, VC, C/C++, Labview, etc., which is exactly the same as the traditional instrument control method. In the battery testing process, the most important issue for customers is not only to ensure the quality of batteries, but also how to increase battery production and reduce production costs. In addition, due to the different electrical characteristics of different types of batteries, the test system must have a certain degree of flexibility in software and hardware to facilitate customers to carry out secondary development on the system. Finally, under the condition of continuous operation of the production line 24 hours a day, the quality and maintenance cost of the system instruments are also an important factor in measuring the battery test system solution. Selection of test system instruments Selection of multi-way switches in battery test systems: In single-chip battery testing, multi-way switches are mainly used to connect different loads or power supplies to the battery for repeated charge and discharge tests. Multi-way switches can also be used to switch measuring instruments. In the ordinary battery testing process, it takes about dozens of switch switching steps to complete all tests on a single battery. The daily production volume of the production line is usually more than 8,000 pieces, and the number of opening and closing times of a single switch in a day can reach more than 150,000 times. Therefore, good switch quality and fast switch switching rate are the key to selecting switch products. Agilent 34980A provides a variety of high-quality switch cards. These switches provide the fastest opening and closing time and the longest switch life among similar products, and can report the working status of each switch in time through the switch count function, so as to replace the switch that is about to fail in advance. In addition, its built-in digital multimeter can directly complete high-precision measurements of various DC signals. It can save investment and improve system integration and test speed.

Selection of multiple power supplies in battery test systems

In battery testing, there are more than two power supplies loaded on the DUT. In addition to powering the fixture of the DUT, these power supplies are also used to charge the battery, 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, the battery is overcharged for no more than 1 second, otherwise it may cause the battery to burn and explode. In order to ensure the test speed, this time is generally limited to a few hundred milliseconds.
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N6700 modular DC power supply, each power supply chassis can be placed in 1U height up to 4 电源模块\'); companyAdEvent.show(this,\'companyAdDiv\',[5,18])"> power modules , forming independent multi-channel power supply. In addition, these power modules are built-in voltage and current measurement function, can monitor the output status, without switching to other measuring instruments. In the automatic test system, the modular power supply system can greatly reduce the size of the multi-channel power supply and reduce the system cost, becoming the first choice for power supply in building test systems today.

Selection of electronic loads in battery test systems

Electronic loads are used to test battery discharge and simulate whether the internal protection circuit can cut off the battery output in time when the battery outputs a large current in a short circuit. In the battery test phase, the large current discharge time cannot exceed 30ms, otherwise it will cause unexpected battery combustion or explosion. Therefore, in order to ensure the safety of the test, this type of test has very high requirements for the response speed of the electronic load and the current change speed.

Agilent provides a variety of electronic load products, among which the fast current change speed can reach up to 107A/S. Built-in 16-bit voltage and current readback function can measure the voltage and current values ​​under working conditions in real time without

You must switch to another device.

Selection of AC internal resistance tester

The internal resistance of the battery is directly related to the quality of the battery cell and the quality of the battery packaging. If the measured internal resistance of the battery is higher than the expected value, it means that the battery quality is likely to have problems. Since lithium-ion batteries are often accompanied by dynamic loads and often generate a large number of current pulses during work, measuring the AC internal resistance of the battery at 1kHz has become the industry standard for measuring battery internal resistance. The lower the battery internal resistance, the more stable the voltage value output by the battery. Therefore, measuring the battery internal resistance at 1kHz will be a very powerful indicator of the battery's ability to regulate its own output voltage under dynamic load conditions . Agilent's dynamic internal resistance tester 4338B can help solve problems in AC internal resistance testing and provide high-speed and accurate measurement results.

With the above instruments, an efficient battery testing system can be quickly established. Most of the instruments have good expansion capabilities, such as the 34980A switch system, which can expand more measurement channels by plugging in cards, and the N6700 can increase the number of power supplies in the system or increase the power supply output power by inserting power modules , etc. This system also has good expansion capabilities. After very simple modifications, it can be used in testing other large-capacity batteries, such as batteries for PDAs, laptops, and digital cameras.