BMS Board testing Of 3310G Series Electronic Loads
BMS Protective Devices
Lithium batteries are widely used in a variety of electronic products and electric vehicles and other devices. In order to protect the lithium battery from catching fire, exploding or any other dangerous condition, the lithium battery must be designed with a Battery Management System （BMS） protection circuit. The BMS ensures the charging voltage does not exceed the maximum safe value of the lithium battery （Over Voltage Protection or OVP） during charge cycles. It also monitors discharge to ensure battery does short-circuit or exceed its rated current （Over Current Protection or OCP）. Finally, internal battery and cell temperatures are monitored for over or under temperature protection （OTP/UTP）.
Previous Prodigit 3310F Series electronic loads were developed with BMS test functions back in 2015 as an option on the 3302F mainframe. The 3310G Series electronic now includes standard BMS test functions. Furthermore, the new Turbo mode allows the short circuit protection current and overcurrent protection to be 2 times larger depending on 3310G model.
The 3310G Series BMS test function for lithium batteries includes short circuit and over current protection modes, which provide a quick, easy and accurate test solution. For BMS short-circuit protection, there is about four times more current available for OCP current testing that needs immediate（uS level）protection action function, use 3311G up to 120 A current load, in the process of high current pull to BMS rated short circuit current, it can verify BMS short circuit protection can do correct action.
In addition, the 3310G series electronic load can also detect the actual operating current value and operating time of the BMS short circuit protection action, that is, the actual operating current value and operating time when the BMS internal MOSFET switch is turned off.
For BMS overcurrent protection, it is between normal operating current and short-circuit current protection, generally higher than 125 % of OCP current, it needs fast （about several hundred mS level） protection action.
3310G series BMS overcurrent （over current during charging and overcurrent during discharge） protection test system with electronic load pull, then confirm whether BMS overcurrent protection is active, when BMS overcurrent protection is not active, increase load current （I Step）. Then, confirm whether the OCP of the BMS is active, and continue the process until the BMS OCP action occurs. Therefore, the BMS OCP test can be scanned by gradually increasing the load current to obtain the current point and action reaction time of the BMS overcurrent protection.
BMS short circuit, overcharge current, over discharge current protection principle
The BMS circuit protection principle is as shown in the figure below. It is to protect the battery by turning off the MOSFET （loop current = 0 A）.
In the BMS, the MOSFET switch is bidirectional. In the normal status, the two switches are ON. Since the two MOSEFT switches have the Rds ON resistance, current flow will cause a voltage drop. Battery BMS is used this feature to detect charge and discharge currents. The MOSFET switching status shown in the figure below is the over-discharge current status. The IC's 3rd pin control MOSFET is ON, this time the discharge switch is OFF （controlled by IC pin 1）.
When the BMS detects a short circuit, over discharge current or low battery voltage, it will turn off the discharge switch to protect the battery.
When the BMS detects an overcharge current or a battery overvoltage, it will turn off the charge switch to protect the battery.
Short-circuit protection (SHORT) test method :
Power supply (PS) & LOAD connection is shown in Figure 2, LOAD test procedure is shown in Figure 3.
In the short-circuit protection test mode, the electronic load will load the maximum current value of the model （for example, 60 A for 3311G or 120 A for Turbo ON）. At the same time, the timer is started to calculate the actual time flowing through the BMS （Note：This time refers to the time between the set threshold current Ith to the BMS action MOSEFT switch OFF, that is, the time lower than the set threshold current Ith. ） in addition, the electronic load will measure the actual maximum short circuit current value, Figure 4 is 4000 mAh mobile power uses the 3311G BMS test oscilloscope current waveform （left figure） and the electronic load power meter to show the short circuit maximum actual current and short circuit protection reaction time （right figure）.
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Overcharge Current Protection ( OCCP ) test method :
The test method is divided into single pulse and continuous step pulse. Single pulse can be used for rapid test. It can be used for a large number of fast tests suitable for the production line. Continuous step pulse can be used to scan the actual over current protection point. Suitable for research and development that needs accurate point.
The power supply (PS) & LOAD connection and test procedures are shown in Figure 5.
In the single-pulse overcurrent protection test mode, the electronic load will be pulled to the set current value （for example, 3311G is the current value between 0 A to 60 A or 120 A when Turbo is ON）, at this time, the electronic load measures the actual maximum overcurrent protection value and the overcurrent response time value. Figure 6 is the 3311G single pulse current BMS overcharge current test program diagram, Figure 7 is the actual test result, the left picture is the oscilloscope current waveform when BMS overcharge current protection. The figure on the right shows the actual test overcharge current value and protection reaction time of the 3311G BMS.
The overcurrent protection test mode of continuous STEP pulse is similar to the single pulse mode. In addition to the initial current setting, the continuous STEP pulse mode increases the time of each STEP, the current increased by each STEP and the current value of the final STEP. Figure 8 is the 3311G single pulse current BMS overcharge current test program diagram. Figure 9 is the actual test result, the left picture is the oscilloscope current waveform diagram when BMS overcharge current protection, the right picture is the actual test overcharge current value of 3311G BMS and Protect the reaction time.
In continuous STEP pulse mode, the maximum overcurrent protection value and overcurrent action reaction time value measured by the electronic load are the measurement results under each STEP. For example, if ISTART is set to 1.000 A, OCT TSTEP is 500 ms, OCP ISTEP is 0.1 A, OCP ISTOP is 5.000 A, the measurement process is the electronic load sink current 1.000 A and test whether the battery BMS operates at 500 ms. If it is, it will measure the action current value and the action reaction time. If the battery BMS is no action under 1.000 A, the electronic load will increase to 1.100 A according to ISTEP setting, and test whether it operates at 500 ms. If it is, it will measure the operating voltage value and action time at 1.100 A, if the battery BMS is no action at 1.100 A. the load current is increased to 1.200 A in the above manner until the final test voltage value of the battery BMS test is 5.000 A.
Single Pulse： Used during quick test
Continuous Step Pulse : Use when scanning the actual overcurrent protection point during charging
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Over current discharge protection （OCDP） test method: Power supply （PS） & LOAD connection and test procedures are shown in Figure 10.
Single Pulse : Used during quick test
OCDP（Over Current Discharge Protection）Test Procedure
The 3311G single pulse current BMS over discharge current test procedure is similar to the BMS overcharge current test. The 3311G BMS function can actually test the overcharge current value and the protection reaction time.
Continuous Step Pulse : Used when the actual overcurrent protection point during scan discharge
OCDP（Over Current Discharge Protection）Test Procedure
The 3311G continuous pulse current BMS over discharge current test procedure is similar to the BMS overcharge current test. The 3311G BMS function can actually test the overcharge current value and reaction time.
The function and actual action response of the battery BMS have been explained in detail. The battery BMS can immediately provide protection and disconnection measures for the abnormal voltage, current, temperature and other conditions of the battery to avoid the occurrence of danger, because the battery BMS is a safety measure that must be 100 % full-featured test verification that security can be ensure, although the test and verification for the battery BMS can use the oscilloscope to measure the current value and action response time of the BMS action, it is undoubted that the oscilloscope can be tested in detail during the development stage, but in a mass production stage, there is a need for rapid and complete testing that there is a limit on capacity production .
For this difficulty, Prodigit integrates the BMS test into the 3310G series electronic load. In addition to the functions of the normal 3310G series, the set test current required for battery BMS testing is increased. Both the current action value and the action response timer are integrated into the 3311G BMS function, allowing a large number of quick tests to verify that the battery BMS becomes a reliable, accurate and fast method.
To test BMS over-current protection, the 3310G load starts to sink current (I start), then checks whether the BMS over-current protection is active. If the BMS over-current protection is not active, the load starts to increase the load current （I Step） and checks whether the BMS OCP is responds. This process continues until the BMS OCP activates. Thus, the BMS OCP test can determine both OCP function current trip level and response time.