6020 ATE provides BMS verification test solutions

3310F electronic load and 6010 ATE provides BMS verification test solutions (Battery Management System)

The popularity of hand-held portable devices – smart phones, notebook computers and tablets – has grown tremendously over the last decade. All these device are battery operated and contain internal rechargeable lithium-ion batteries. Other popular devices and appliances like electric bicycles, scooters and electric vehicles are also equipped with various types and sizes of battery packs required to power them. In addition to providing power, these batteries must also be able to cope with abnormal load and charge conditions that could lead to fires and even explosions if not properly handled. As a result, all these devices must incorporate sophisticated battery management systems (BMS) to ensure operator safety. Recent news articles on exploding smart phones have underscored this need for built-in safety measures in a dramatic way.
A battery management system (BMS) consist of an electric circuit board connected directly to the internal rechargeable batteries that monitors battery voltage, charge current, discharge current, battery cell temperature and state of charge. It also provides information to the user on battery capacity, recharge time and power consumption as needed. When any dangerous or abnormal battery conditions are detected, the BMS circuit is responsible for disconnecting the charging device to avoid the risk of battery damage and or fire. Examples of abnormal battery conditions are:

a. Over current conditions for both charging and discharging modes
b. Charging voltage that exceed safe voltage limits
c. During discharge conditions, under voltage level indicating over-discharging
d. Battery temperature that is too high
e. Battery temperature that is too low

In order for the BMS to ensure that the batteries can be operated within their safe operating area, the BMS has an internal switch (typically a solid-state semiconductor MOSFET Switch). When the battery operates outside of the safety zone, this internal switch will disconnect the charging circuit (OPEN) from the battery to ensure its safety.

Prior to installing a BMS with its battery pack, the BMS functionality must be tested to ensure the BMS design is suitable for all potential abnormal battery conditions that can occur during the final products useful life. This is necessary to ensure safe operator and limit the manufacturer’s product liability.

Once the individual BMS circuit has been tested and verified, it must be integrated with the battery cells into the finished product and undergo final system level functional test to ensure compliance with applicable product standards.

The new BMS Test Adaptor option available from PRODIGIT Electronics Loads offers two kinds of comprehensive solutions for testing and certification of BMS circuit design on all PRODIGIT DC loads as well as the 6010 ATE test system. This application note covers operation of this new option in combination with the 3310F Series DC loads. This includes simulation of battery charging, discharging and temperature related and other abnormal battery conditions. The new test adaptor supports the ability to quickly test actual BMS operating parameters including over-charge and under-charge currents and BMS circuit response times. It also allows simulation of battery over or under temperature conditions to test the BMS ability to adjust charging current accordingly. For further details on BMS Temperature response testing, refer to the “Battery charger and temperature test solution” section below.

The following sections cover application and operation of the PRODIGIT 3310F DC load series with the BMS test option for BMS performance testing.

1. BMS short circuit, over current charge, over current discharge protection principle

The circuit diagram shown below illustrates principle circuit operation of a typical BMS design. A MOSFET switch between the charger and the battery cells is controlled by the BMS circuit to turn off charging current (Loop Current = 0 Adc) to protect the battery.

The MOSFET used in BMS applications acts as a two-way switch. In normal state, both switches are ON for respective charging or discharging conditions. Since both MOSFET switches have an Rds on resistance, some voltage drop will occur across each switch when current flows through them. The BMS circuit relies on the detection of this voltage drop to determine charge and discharge conditions in effect. The figure below shows the FET switches in their over-current condition state. Pin 3 of the IC controls the FET to the ON state. The discharge FET controlled by pin1 is OFF in this condition.When the BMS circuit detects a SHORT circuit, over discharge current or battery over-charge condition (battery voltage too low), the discharge switch will turn OFF to protect the battery from damage.When the BMS circuit detects a battery over-charge condition (battery voltage too high), the charge switch will turn OFF to protect the battery from damage.

When the battery is accidentally short circuit or over current, IC pin 2 voltage (partial voltage of the MOSFET threshold resistance) is greater than the over current detection threshold, IC pin 1 output low, the discharge MOSFET is turned off to stop discharge.

Figure 1 typical BMS circuitry

2. Short Circuit Protection Test Method.

Figure 2 below shows the DC power supply (PS) used to charge the battery and the load connections required for the test procedure shown in Figure 3.During SHORT circuit protection mode, the electronic load will sink current at its maximum current rating to simulate a battery short circuit condition. For a model 3311F load, this will be equivalent to 60 Adc. At the same time, the load starts a timer to measure the actual amount of time current flow through the BMS. Note that this time represents the time from the threshold current Ith to the BMS engages the MOSFET switch to the OFF state and is below the threshold current Ith time (??). The load will also measure the actual maximum short-circuit current. Figure 4 shows a scope trace of a 4000 mAh mobile device battery pack under short circuit conditions applied by a 3311F DC load with BMS test adaptor (see left). The meter of the 3311F load displays the maximum short circuit current and the BMS protection SHORT circuit protection delay (see right).

PS Simulates Battery Electronic Load simulates the current of electronic device

Figure 2 Equivalent Block Diagram for BMS discharge operation

SHORT Protection Test Procedure

Figure 3 The procedure of 3311F with BMS for SHORT current test procedure

Figure 4 The waveform of 4000mAh power Bank at real SHORT test

3. Over Current Charge Protection (OCCP) Test Method.

These tests can be performed in a number of different ways such as Single Pulse mode, Continuous Mode and Step Pulse mode. Single Pulse mode is used for fast testing and is suitable for high volume production line applications. Continuous Step Pulse mode can be used to scan for the actual over current protection point and is most suitable for Research and Development applications requiring precise response time and current characterization. Relevant Power Supply (PS) and LOAD connection diagrams and test procedures are shown in Figure 5.

3.1 Single Pulse over-current protection test mode. In this mode, the electronic load will sink the programmed load current. For a 3311F model, the available current range would be 0 to 60 Adc. At that point, the load will measure the actual current value of the over current protection and over current response time demanded by the BMS circuit. Figure 6 shows a BMS overcharge test procedure using the 3311F in single pulse current mode. Figure 7 is the actual measured test current with the oscilloscope capture of the current waveform. The figure on the right is the 3311F display of the actual BMS test over charge current value and the BMS protection response time.

3.2 Continuous Step Pulse over-current protection test mode. This mode is similar to the single pulse test mode except the pulse current setting and the time for each step pulse is increased with each step until the final step current value is reached. Figure 8 shows a BMS overcharge test procedure using the 3311F in single pulse current mode. Figure 9 is the actual measured test current with the oscilloscope capture of the current waveform. The figure on the right is the 3311F display of the actual BMS test over charge current value and the BMS protection response time.
In Continuous STEP pulse mode, the actual over current protection value and over current response time value measuring by electronic load is the test result for each STEP. For example, if ISTART is set to 1.000A OCT TSTEP and ISTART as 500msec, OCP ISTEP is 0.1A and OCP ISTOP is 5.000A, the measurement cycle will start by pulling 1.000A and check to see if the BMS responds within 500msec. If the BMS responds, the current and response time will be recorded. If the BMS does not respond to the 1.000A current, the load will proceed to the next test level of 1.100A and wait for a BMS response within 500msec again. This process will repeat until the BMS responds within the set time interval or the final current pulse value of 5.000A is reached.

Simulating battery charge current by electronic load Simulating charge operation bypower supply (PS)

Figure 5 Equivalent Block Diagram for BMS charge operation

3.3 Single pulse : use in fast test

OCCP(Over Current Charge Protection)Test Procedure

Figure 6 3311F with BMS for over current charge test procedure ( single pulse current )

Figure 7 3311F with BMS for over current charge test result ( single pulse current )

3.4 Continuous step pulse : using the actual over current protection when scanning charge

OCCP(Over Current Charge Protection)Test Procedure

Figure 8 3311F with BMS for over current charge test procedure ( single pulse current )

Figure 9 3311F with BMS for over current charge test result ( continuous STEP pulse )

4. Over Current Discharge Protection (OCDP) Test Method.

Relevant Power Supply (PS) and LOAD connection diagrams and test procedures are shown in Figure 10.

Simulating battery discharge operation bypower supply Simulating discharge operation byelectronic load

Figure 10 Equivalent Block Diagram for BMS discharge operation

4.1 Single Pulse Method. This method is fast and appropriate for high volume production test applications.
Over Current Discharge Protection (OCDP) Test Procedure.

Figure 11 shows a single pulse current from the 3311F load to test the BMS over current discharge.

Figure 12 shows the actual test results. The image on the left is the actual measured test current with the oscilloscope capture of the current waveform. The figure on the right is the 3311F display of the actual BMS test over current discharge value and the BMS protection response time.

Figure 11 3311F with BMS for over current discharge test procedure

Figure 12 3311F with BMS for over current discharge test result ( single pulse )

4.2 Continuous Step Pulse.

Over Current Discharge Protection (OCDP) Test Procedure.
Figure 13 shows the continuous pulse current BMS over discharge current test procedure of the 3311F load to test the BMS over current discharge. Figure 14 shows the actual test results. The image on the left is the actual measured test current with the oscilloscope capture of the current waveform. The figure on the right is the 3311F display of the actual BMS test over current discharge value and the BMS protection response time.

Figure 13 3311F with BMS for over current discharge test procedure ( continuous STEP pulse )

Figure 14 3311F with BMS for over current discharge test result ( continuous STEP pulse )

5. Previous paragraphs detailed the BMS functions and its response to actual battery conditions.
As described, the BMS can provide immediate disconnection protection measures as a result of abnormal battery conditions of voltage, current and temperature to avoid hazardous conditions. Since the BMS is a product safety device, it must be 100% functionally tested and verified in order to ensure product safety. This testing can be done using an oscilloscope during product development but during high volume production testing, the need exists for fast and consistent comprehensive testing that does not rely too much on operator skills. The integration of the BMS test option into PRODIGIT electronics loads provides such a fast and easy test method that obtains the same results as would be possible using an oscilloscope while at the same time simplifying and automating the test process.
Available test functions of the BMS option are: Short Circuit, OCCP and OCDPOperating Instruction for each mode are as follows :

5.1 Set BMS mode to ON in the Config menu. This will place the front panel OCP/Short Test button in
BMS test mode. If BMS mode is turned OFF, the OCP/OPP/Short buttons operate in normal mode.

5.2 SHORT Test. When in BMS mode, a P+ and P- display indication is available for short circuit

protection testing. This tests needs to measure the short circuit current and protection response time of the BMS under test. The SHORT key can be used to set the short test time from 0.010 to 10.000 msec. The default setting is 1msec. The threshold current level Ith can be set from 0.01 to 60Adc depending on load model. Press the START key to start a BMS short test. During testing, the display will show “SHORT” TEST during measurements. When completed, the measured short circuit current Im is shown. The second line of the LCD displays the short circuit current and the third line displays the protection response time.

5.3 Over Current Protection Test (OCCP/OCDP). This test checks the BMS over current charge protection (OCCP) and over current discharge protection (OCDP) functions. This requires measurement of the current levels applied and the response time of the BMS circuit under test. The main different between both test is in the connection of the DC power supply and the LOAD to the BMS circuit.

To set these tests, press the OCP key and set in the following order: Istart -> Tstep (1 through 1000 msec) -> Istep -> Istop -> Ith (0.01A through Istart). Press the START key to start load testing from the Istart current level and set the time out (Tstep). If the BMS does not respond to the current test level, the current level is increased by the step size Istep – if Istep = 0, the test will end. Once the BMS response in the time interval set, the load reports the current and response time. During testing, OCP TEST will be displayed on the LCD. When completed, the measured short circuit current Im is shown. The second line of the LCD displays the last test current and the third line displays the protection response time.

Note: When in PULSE test mode, set Istart and Tstep value only. Press the START key to start the test.

5.4 The relevant technical specifications for the BMS option as installed in a 3311F DC load model are shown in the table below. This includes SHORT and OCP test modes. For BMS specifications on other DC Load model, please contact PRODIGIT sales.

Table 1 The specification of 3311F with BMS option

5.5 As is clear from this application note, testing of a BMS circuit with the BMS option requires the use of a DC power supply for charging the battery during testing. If the BMS is already integrated in the final product with the battery cells, no external DC power supply is needed as test can be applied to the integrated assembly. The PRODIGIT 6010 ATE System includes a DC power supply as required for BMS circuit testing. The BMS charge and discharge connector switches can be controlled directly by the 6010 ATE system.

5.6 Based on the information provided in this application note, it is evident that the measurements provided by the BMS option are the same as those that can be obtained using a digital storage scope. Moreover, the required test levels and parameters can be easily programmed on the LOAD which provides increased flexibility, accuracy and easy of testing. Also, the 6010 ATE system supports all PRODIGIT DC loads equipped with the BMS option for automated product testing.

Almost all series electronic load can be installed with BMS option, such as 3310 series, 34000 series, 36000 series electronic load, please contact Prodigit sales office or distributor in your area.

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3310F DC Electronic Load
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2020-05-15

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